We present the first combined oscillation analysis of multiple atmospheric neutrino datasets, featuring data from Super-Kamiokande, IceCube-DeepCore, and KM3NeT/ORCA together with reactor data from Daya Bay. Such combinations have long been considered infeasible outside experimental collaborations; we demonstrate that a unified physics model can simultaneously describe all datasets with no significant parameter tensions. Fitting 839048 events across 1536 bins with 91 parameters, our combined analysis yields competitive measurements of the neutrino mixing parameters, and prefers the Normal over the Inverted Mass Ordering.

We present global limits for Majorana neutrino masses by combining latest results from neutrinoless double-beta ($0νββ$) decay searches and ab initio nuclear theory. Limits are derived in a Bayesian framework utilizing likelihood functions from a suite of $0νββ$-decay experiments in conjunction with nuclear matrix elements calculated from nuclear and electroweak forces derived from chiral effective field theory and implemented in the in-medium similarity renormalization group many-body approach. In contrast to nuclear models, ab initio results indicate that the current generation of $0νββ$-decay experiments have likely \textit{not} yet reached sensitivities required to probe the mass regime allowed by neutrino-oscillation data, where the combined bounds are notably stronger than those given by individual experiments. Finally, from predicted sensitivities of next-generation searches, we show that, while no one individual experiment fully covers the inverted mass ordering, this can be achieved from combined contributions from the four key isotopes: $^{76}$Ge, $^{100}$Mo, $^{130}$Te, and $^{136}$Xe.

The flavor puzzle remains one of the biggest open questions in particle theory to date and upcoming results from neutrino experiments will have a large impact on its potential solution in the future. While some classes of leptonic flavor models are difficult to constrain with current data, this will change in the coming years as several yet unknown quantities, like the neutrino mass ordering and the octant of $θ_{23}$, will be determined, and the CP-violating quantity $δ$ will be measured with some precision. In addition, significant improvements in the precision of the other oscillation parameters, notably $θ_{12}$, is also expected to impact our understanding of flavor. Together with anticipated improvements on the absolute neutrino mass scale determination from the combination of cosmological data sets or beta decay endpoint spectrum measurements, upcoming experiments will lead to a refined picture of our understanding of flavor in the lepton sector. In this paper, we show exactly how flavor model predictions relate to expected measurements. Five popular classes of leptonic flavor model predictions are considered: mass sum rules, one and two texture-zeros for both Dirac and Majorana neutrinos, charged lepton corrections, modular symmetries, and constrained sequential dominance. We discuss correlations, degeneracies, and discrimination capabilities in the context of the expected measurements from upcoming experiments. We also highlight how different flavor model predictions can be differentiated and the roles each upcoming observable has on flavor model predictions. We anticipate that the precision targeted in future measurements will be sufficient to dramatically reduce the number of viable leptonic flavor models, will allow us to disentangle them, and could hopefully begin to shed light on the answer to the flavor puzzle.

Determining the neutrino mass ordering remains a central open problem in particle physics. While next-generation long-baseline experiments are expected to resolve this question, current data provide limited sensitivity because the spectral differences between normal and inverted ordering are subtle and entangled with parameter degeneracies. We investigate a machine-learning strategy for mass-ordering determination using a feed-forward neural-network classifier trained on synthetic long-baseline datasets generated with three-flavour oscillation probabilities, matter effects, and statistical fluctuations. We evaluate the classifier against standard $χ^2$ and $\log\mathcal{L}$ approaches using common discrimination metrics, including receiver-operating-characteristic curves, to quantify sensitivity and to illustrate how operating points can be selected to prioritise purity or efficiency. We find that the neural network achieves performance comparable to conventional fits for the scenarios studied, providing a flexible, independent cross-check of established analyses. The framework can be extended to incorporate systematic uncertainties and to explore joint inference of oscillation parameters, and it may also serve as a pedagogical tool for introducing machine-learning methods in neutrino physics.

Constraining the cosmic neutrino background (C$ν$B) represents a major experimental challenge in cosmology. Recent studies have suggested that relic neutrinos boosted by ultra-high-energy cosmic rays (UHECRs) may generate observable diffuse neutrino fluxes. Previous estimates have not effectively propagated the primary cosmic rays, often neglecting crucial energy losses and the unavoidable, competing interactions with diffuse photon backgrounds. Here we revisit these expectations using a realistic Monte Carlo propagation framework. This approach allows us to consistently incorporate cosmic ray energy losses, nuclear photodisintegration, and production of secondary neutrinos. We show that interactions with diffuse photon backgrounds strongly suppress the boosted relic neutrino flux predicted in simplified propagation scenarios. Furthermore, we demonstrate that to produce any observable suppression on the UHECR energy spectrum at Earth, or for the boosted C$ν$B component to become comparable to the cosmogenic neutrino flux, the C$ν$B density must be enhanced by a factor, the so-called overdensity, of extreme magnitude ($η\gtrsim 10^{8}$).

Recent measurements of the diffuse cosmic neutrino flux by IceCube show evidence for a spectral break at an energy near $E_ν\sim 30$ TeV. In this letter, we suggest that this feature may be due to the $Δ$-baryon resonance in $pγ$ interactions. We show that the measured spectrum, including the observed break, can be naturally accommodated by a flux of protons accelerated with a spectrum $dN_p /dE_p \propto E_p^{-3.1}$ interacting with X-rays of typical energy $E_γ \sim 0.3\,{\rm keV}$. We also point out that the presence of this spectral break significantly reduces the contribution of neutrino sources to the isotropic gamma-ray background, alleviating the longstanding tension between these measurements. In the $Δ$-resonance scenario, the gamma rays accompanying neutrino production cascade down to MeV-GeV energies and contribute at the $\sim 10\%$ level to the isotropic gamma-ray background at $\sim 3$~GeV. If our proposal is realized, it may imply that we have identified the dominant sources that produce the extragalactic cosmic rays.

Neutrino rest mass enables left-handed states to "flip" to right-handed states and vice versa. In-medium effects can enhance the probability for such spin-flip. We demonstrate that a full many-body calculation of this process in neutrino-dense environments can lead to spin-flip probabilities that exceed by orders of magnitude those calculated with mean-field treatments. We study simple configurations with a few neutrinos in well-defined momentum states, for which we show that the helicity conversion enhancement is connected to many-body momentum exchange. Such an effect would therefore be missed in a calculation that considers only forward processes. We speculate on the potential astrophysical implications of these results and the range of applicability of our calculation and its limitations.

Astrophysical neutrinos provide a unique probe of neutrino flavor changes over cosmological baselines. While the tau component of the neutrino flux is expected to arise almost entirely from mixing, current measurements rely primarily on rare double-cascade signatures. We investigate a complementary method to measure the tau fraction using the visible inelasticity of starting track events in neutrino telescopes. Muonic decays of tau leptons produce tracks with systematically larger visible inelasticity than those from muon neutrino interactions, potentially enabling statistical separation of the two flavors. Using realistic IceCube exposures and detector performance, we show that this observable already yields competitive sensitivity to the tau-to-muon flux ratio, $R_{τμ}$, achievable with existing data. This approach may further enable flavor measurements of individual sources and the selection of tau-enhanced source catalogs. Starting-track inelasticity thus provides a powerful and immediately accessible probe of astrophysical neutrino flavor and of potential physics beyond standard neutrino mixing.

Recent Super-Kamiokande analyses of the diffuse supernova neutrino background, based on data across all SK phases, indicate a mild preference over the zero-DSNB hypothesis at the level of about $2.3σ$ with electron-like antineutrino events at $E_{\barν_e} \simeq 20\,\mathrm{MeV}$. We investigate whether this excess can be explained by MeV-scale dark matter annihilation into neutrinos in a $\mathrm{U}(1)_{L_μ- L_τ}$ model. The dark matter is a Dirac fermion with $m_χ\simeq 22\,\mathrm{MeV}$ that annihilates via a light $Z'$ mediator into $ν_μ\barν_μ$ and $ν_τ\barν_τ$, which are partly converted into $\barν_e$ through flavor oscillations. We find that this scenario simultaneously accounts for the excess and the observed relic abundance via thermal freeze-out. We further discuss the relevant laboratory and cosmological constraints, including neutrino trident production, NA64-$μ$, Borexino, and the contribution to $ΔN_\mathrm{eff}$.

Recently, dark matter direct-detection experiments have begun their exploration of the ``neutrino fog,'' providing the first hints of detection of solar neutrinos scattering elastically with the nuclei in the detector. In this work, we investigate how such observations can be used to uniquely explore sterile-neutrino parameter space, specifically through mixing with $ν_μ$ and $ν_τ$. While it is challenging to constrain these parameters with current observations -- PandaX, XENONnT, and LZ -- we demonstrate how future measurements (with modest improvements to exposure and systematic uncertainties) can provide useful, complementary information in the search for sterile neutrinos. With an ideal, next-generation direct-detection facility (${\sim}3000$ ton-yr), we can probe parameter space previously unexplored by other methods, including long-baseline and atmospheric searches for this class of new physics.

Testing the unitarity of the lepton mixing matrix, in a manner analogous to the unitarity tests of the CKM matrix in the quark sector, is an important step toward probing physics beyond the standard three-generation framework. In long baseline neutrino oscillation experiments, the formula of the oscillation probabilities can be written as a sum of terms with various combinations of the mixing-matrix elements, and their coefficients depend differently on energy. By observing the spectral information of long baseline experiments such as T2HK and a future neutrino factory at J-PARC with a $ν_e$ beam, the elements of the mixing matrix can be extracted without assuming a specific parametrization of the mixing matrix. We investigate how such an extraction method can be applied to neutrino oscillations by taking into account matter effects, and discuss how one can test unitarity of the mixing matrix in future long baseline experiments. As a concrete example, we examine the unitarity test by using a four-generation model, where we look at a quantity which should be vanishing in a unitary model. Among possible combinations of measurements, the most powerful test can be provided from the energy spectra of the CP-conjugate appearance channels $ν_μ\to ν_e$ and $\barν_μ\to \barν_e$ at T2HK, as well as from the T-conjugate pair $ν_μ\to ν_e$ and $ν_e \to ν_μ$ available at neutrino factories.

Super-Kamiokande has reported a small excess of electron antineutrino events in the 20 MeV energy range, in the search for the diffuse supernova neutrino background. We interpret this signal as a possible indication of dark matter that annihilates dominantly into neutrinos, pointing to a thermal dark matter candidate with $s$-wave annihilation and with mass in the tens of MeV range. This mass scale naturally fits into rich dark sector extensions of the Standard Model. Neutrino experiments, including JUNO, will be able to test this hypothesis in the coming years.

We propose a new approach to measuring the CP-violating phase in neutrino mixing using atmospheric neutrinos, differing significantly from prior work. We develop an up-down flux ratio for sub-GeV atmospheric neutrinos that incorporates realistic detection effects and reduces systematic uncertainties. For the example of Hyper-Kamiokande -- the first experiment with sufficient atmospheric-neutrino statistics in this energy range -- our approach can surpass the sensitivity of the Tokai to Hyper-Kamiokande (T2HK) long-baseline experiment near $\mathit{δ_\mathrm{CP} = 90^\circ}$ and $\mathit{270^\circ}$. Realizing this potential will require additional, but realistic, work to reduce theoretical uncertainties. Success will provide an important, complementary probe to multi-\$1B accelerator-based experiments.

Neutrino oscillation experiments present anomalous results across a vast range of baselines and energies. Here we show that a 3+1 scenario in which sterile neutrinos feel a novel matter potential $V_s$ proportional to background density of ordinary or (asymmetric) dark matter is able to explain several anomalies. At low-energies ($E\lesssim$ 1 TeV) the model behaves as an effective 3-flavor NSI-like scheme among active flavors and eliminates the tension between the two LBL experiments NOvA and T2K provided that the potential is negative and the two sterile mixing angles $θ_{14}$ and $θ_{24}$ are non-zero. A further indication in favor of a negative non-zero potential comes from the anomalous excess of $ν_e$-like events observed in Super-Kamiokande atmospheric neutrinos, which, in the new scenario is explained by a modification of the 3-flavor resonance at few GeV. A high energies ($E\gtrsim $ 1 TeV) the new framework reveals its 4-flavor nature and produces a resonant behavior at $E \simeq$ 10 TeV as hinted at by IceCube. We identify an irreducible 3-level dynamics generating a new resonance in the $(ν_e, ν_μ)$ sector intertwined with two conventional resonances in the $(ν_e, ν_s$) and $(ν_μ, ν_s)$ systems. The novel amplification mechanism manifests with the emergence of effective mixing angles in matter ($θ_{12}^m$ or $θ_{13}^m$) involving active neutrinos. The scenario requires values of $f = V_s/|V_{NC}| \sim -20 $, $Δm^2_{41} \sim 60 $ eV$^2$, $|U_{e4}|^2\simeq \sin^2θ_{14} \simeq 0.01-0.03$ and $|U_{\mu4}|^2 \simeq \sin^2θ_{24}\simeq 10^{-4}-10^{-3}$. Such a very small size of $|U_{\mu4}|^2$ eliminates the tension between IceCube and the other $ν_μ$ disappearance searches. The model can be directly probed by KATRIN, which is very sensitive to the electron-sterile neutrino admixture in the region of high $Δm^2_{41}$.

We study the sensitivity of the diffuse high-energy neutrino flux observed in IceCube to new-physics effects resulting in an exponential flux attenuation along the trajectory, such as invisible neutrino decay or new interactions with the background encountered during propagation. We argue that, even though the sources and production redshifts of these astrophysical neutrinos are unknown, conservative energy-conservation arguments allow to severely constrain neutrino loss in most scenarios beyond the strongest existing bounds. By performing a fit to the High-Energy Starting Events from IceCube, we quantify the bounds and study their variation with the energy dependence of the attenuation, the assumed redshift distribution of the neutrino sources, and whether the attenuation affects neutrinos exclusively or no. We also show that including an energy-dependent attenuation at the level allowed in the fit may impact the determination of the spectral index of the diffuse flux.

This work presents the first comprehensive phenomenological analysis of the newly released Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) data on germanium, measured by the COHERENT collaboration at the Spallation Neutron Source. Leveraging the unprecedented precision of this dataset, we provide state-of-the-art determinations of key Standard Model and nuclear physics parameters. Specifically, we extract updated constraints on the weak mixing angle, the neutrino charge radii, and we perform a detailed extraction of the neutron root-mean-square radius of germanium nuclei. Additionally, we use these results to evaluate scenarios beyond the Standard Model, placing robust bounds on neutrino non-standard interactions. To maximize the statistical power and robustness of our findings, whenever possible, we perform a global combined analysis incorporating previous COHERENT measurements along with reactor antineutrino data from the CONUS+, TEXONO, and $ν$GeN experiments as well as dark-matter experiments.

The collapse of supermassive stars (SMSs, $M\gtrsim10^4\,M_\odot$) to black holes is accompanied by a prodigious flux of neutrinos of all flavors. These are produced thermally via $e^\pm$ annihilations, mostly in the core and just before gravitational trapped surface formation. There, the ratio of fluxes for $ν_e\barν_e$-pairs to $ν_μ\barν_μ/ν_τ\barν_τ$-pairs is $\sim$\,5-to-1. This is because at SMS temperature scales, $ν_e\barν_e$ pairs have both charged and neutral current production channels, whereas $ν_μ\barν_μ/ν_τ\barν_τ$-pairs only have neutral current production channels. We point out that the typical energies of these neutrinos, and the run of density in collapsing radiation-dominated supermassive configurations, leads to Mikheyev-Smirnov-Wolfenstein (MSW) resonances inside these objects for the atmospheric neutrino mass splitting scale, $Δm^2_\mathrm{atm.}\sim2.4\times10^{-3}$ eV$^2$. In the normal neutrino mass hierarchy, adiabatic flavor transformation through the MSW resonances would then swap the fluxes $ν_e\leftrightharpoonsν_{μ,τ}$, whereas, in the inverted neutrino mass hierarchy, the anti-neutrino fluxes are swapped, $\barν_e\leftrightharpoons\barν_{μ,τ}$. We also examine the prospects for collective neutrino flavor oscillations in these environments. Implications for flavor oscillation's effects on neutrino energy deposition and neutrino-induced nucleosynthesis in the SMS's outer layers are examined, as are prospects for detections of SMS collapses through various means.

We simulate a self-interacting three-flavor neutrino system within a core-collapse supernova using a hybrid classical-quantum algorithm on a qutrit computer. Based on the Dirac-Frenkel evolution equations, we employ a variation of the quantum-assisted simulator (QAS) to calculate the system's time evolution operator by performing qutrit Hadamard tests to find expectation values of unitary operators in the Hamiltonian. The time evolution simulation is then done classically. We find that the hybrid algorithm produces results comparable to an exact numerical integration out to times of $t \approx 30 \,ω_0^{-1}$ with time step $δt = 0.005 \,ω_0^{-1}$, where $ω_0$ is the energy scale of the single neutrino vacuum oscillations. We discuss the lessons learned in simulating neutrino systems using this hybrid quantum-classical algorithm, along with the advantages it offers over quantum Trotterization.

Neutrino oscillations provide crucial insights into fundamental particle physics, with two-flavor approximations effectively describing reactor and atmospheric phenomena. This paper explores the use of Physics-Informed Neural Networks (PINNs) to solve the governing differential equations for neutrino evolution in both vacuum and matter environments. We review the theoretical framework, including vacuum mixing and the Mikheyev-Smirnov-Wolfenstein (MSW) effect in matter, and demonstrate PINN implementations for vacuum and constant-density profiles. This Machine learning based approach for reactor (low-energy) and atmospheric (high-energy) neutrinos shows high precision similar to analytical solutions, with mean squared errors of the order of \(10^{-3}-10^{-4)\). Although this work focuses on solving the evolution equation in general cases, we discuss the significant potential advantages of PINNs over traditional solvers, without any mesh requirements, high-dimensionality reduction, and applicability to complex geometries, along with future extensions to three-flavor effects.

Sufficiently strong electric fields can produce charged-particle pairs via the Schwinger effect. We argue that steep matter-density gradients, as can arise in neutron star interiors, would analogously produce neutrino-antineutrino pairs. We then discuss observational signatures of these gradient-produced (anti)neutrinos and how they could provide new probes of neutron-star structure and baryon-dense QCD.

Neutrino experiments are often limited by low statistics, sizable systematic uncertainties, and coarse observable binning, which can hinder discrimination among competing beyond-the-Standard-Model (BSM) explanations of anomalous signals. In particular, analyses based primarily on total event-rate differences are vulnerable to source-normalization uncertainties and to degeneracies among models that induce similar inclusive yields. Using stopped-pion coherent elastic neutrino-nucleus scattering (CE$ν$NS) as a benchmark environment, we study how much model-discrimination power can be obtained from correlations in baseline, recoil energy, and timing that are less sensitive to the total rate. As benchmark BSM scenarios, we consider a $3+1$ sterile-neutrino framework and neutral-current non-standard neutrino interactions (NSI). We show with a likelihood-based analysis that these scenarios can be distinguished in nontrivial regions of parameter space once multidimensional shape information is retained. We further demonstrate with convolutional neural networks that substantial discrimination remains possible even after the total event rate is explicitly removed from the input, indicating that the relevant information is genuinely encoded in the shape of the CE$ν$NS distribution. Finally, through multi-class classification within the sterile parameter space, we show that in favorable regions the same observables can support approximate localization of the underlying sterile-neutrino benchmark point. Our results highlight the complementary roles of conventional and machine-learning-based inference in moving neutrino new-physics searches from anomaly detection to physics interpretation.

The determination of leptonic CP violation is a primary goal of future long-baseline neutrino experiments such as DUNE and T2HK. The extraction of $δ_{\mathrm{CP}}$ relies on the near-to-far extrapolation and on the assumed knowledge of the cross-section ratios $σ_{ν_e}/σ_{ν_μ}$ and $σ_{\barν_e}/σ_{\barν_μ}$, which are typically inferred under theoretical assumptions such as lepton universality and depend on nuclear modeling. In this work, we quantify how much of the sensitivity of DUNE and T2HK arises from these assumptions by performing a model-agnostic, data-driven estimation of systematic uncertainties in $ν_e$ and $\barν_e$ cross sections. We find that adopting such an agnostic approach can substantially degrade the CP-violation sensitivity, reducing it by nearly $3σ$ at maximal CP violation for DUNE, and $4σ$ for T2HK. We then assess the impact of the proposed $ν$SCOPE experiment, which, through a combination of neutrino tagging and the Narrow-Band Off-Axis technique, can provide percent-level measurements of $σ_{ν_μ}$ and $σ_{\barν_μ}$ and constrain the ratio $σ_{ν_e}/σ_{ν_μ}$ at the $\sim 2\%$ level. We show that including prospective $ν$SCOPE measurements largely restores the lost sensitivity, highlighting that precise external cross-section measurements may be essential for a fully robust determination of $δ_{\mathrm{CP}}$ and for breaking its degeneracy with nuclear mis-modeling or possible new physics affecting neutrino detection.

Upcoming long-baseline neutrino oscillation experiments such as DUNE aim to achieve unprecedented precision, but their physics reach is ultimately constrained by systematic uncertainties in neutrino flux predictions and neutrino-nucleus cross sections. These limitations are especially critical for new-physics searches in neutrino oscillations at the near detector, including non-unitarity and sterile neutrinos, where the signal manifests as small distortions in the energy spectrum and is therefore highly sensitive to spectral uncertainties. The PRISM (Precision Reaction Independent Spectrum Measurement) technique offers a robust strategy to mitigate these effects by exploiting measurements at multiple off-axis angles, effectively providing a data-driven handle to reduce systematics. In this work, we demonstrate that PRISM can significantly reduce the impact of large systematic uncertainties, restoring sensitivity to non-unitarity and sterile neutrino scenarios in the electron and muon sectors to a level comparable to that obtained with small spectral uncertainties. We also include the results for the $τ$ sector with PRISM; however, in this case, since the majority of the flux measured at off-axis angles lies below the $τ$ production threshold, we find the improvement to be marginal. As part of this work, we have obtained neutrino and antineutrino fluxes for different off-axis angles with higher statistics than those provided by the DUNE collaboration. We make available these fluxes as auxiliary material to this manuscript.

At long-baseline neutrino experiments, neutral-current (NC) events accumulate in large numbers but are seldom exploited for new physics searches. We demonstrate their potential using non-standard neutrino interactions (NSI) with quarks as a case study. Charged-current (CC) analyses constrain NSI through matter effects on neutrino propagation, which probe almost exclusively the isoscalar combination of up- and down-quark couplings; the orthogonal isovector combination is suppressed by a factor of $\sim$100. Because NSI also modify NC cross sections in a flavor-dependent way, NC events become sensitive to oscillations: the far-to-near detector ratio acquires a dependence on the beam's flavor composition that probes both isoscalar and isovector couplings with comparable weight. Using existing NOvA data and DUNE projections, we derive the first bounded constraints on isovector NSI from a long-baseline experiment and show that combining CC and NC measurements resolves the individual quark couplings, breaking a degeneracy that persists in either analysis alone.

Decays of heavier neutrino mass eigenstates into lighter ones, while very slow in the Standard Model, can be significantly enhanced in scenarios with more than three neutrino flavours, or in models with new ultra-light particles such as Majorons. A full theoretical description is challenging due to the intricate interplay between oscillations and decay, interference between different decay channels, and the possibility of multi-step decay cascades. In this paper, we develop a fully general description of arbitrarily complex systems of oscillating and decaying neutrinos using methods from the theory of open quantum systems. Notably, we demonstrate how such systems can be implemented using the Lindblad master equation, the Liouvillian superoperator, as well as Kraus operators. The last two methods eschew the need for solving a differential equation, thereby showing superior numerical performance.

The unprecedented precision now being achieved in the measurement of the Pontecorvo--Maki--Nakagawa--Sakata (PMNS) lepton mixing matrix opens a new window onto the underlying structure of the neutrino mass matrix and the possibly associated flavor symmetries. In this work, we investigate the constraints imposed on the unitary matrix $U_ν$ that diagonalises the neutrino mass matrix, under the hypothesis that the charged-lepton mixing matrix $U_l$ consists of a single two-by-two rotation in one of the three sectors: (1,2), (1,3), or (2,3). For this analysis, we considered the latest global fit which incorporates the precision measurement of $θ_{12}$ from the JUNO experiment. For each scenario, we also derive analytical expressions for the entries of $U_ν$ in terms of the measured PMNS parameters to obtain compact sum-rule-like formulae.

The vast majority of extensions of the Standard Model affecting the number of effective relativistic neutrino species ($N_{\rm eff}$) do so additively, namely, they enhance this quantity with some light state contributing to dark radiation. In this work, we consider precisely the opposite case: new physics scenarios that can lead to $N_{\rm eff} < 3$ that are consistent with all known cosmological, astrophysical, and laboratory data. We are motivated by three main reasons: 1) a recent measurement from ACT and SPT in combination with Planck that leads to $N_{\rm eff} = 2.81\pm0.12$, 2) by a new and powerful measurement of the primordial helium abundance, which anchors $N_{\rm eff}$ to be very close to the Standard Model value one second after the Big Bang, 3) by the deployment of the Simons Observatory which will provide precise tests of the radiation content in the Universe and which may detect with a high significance cosmologies with $N_{\rm eff}<3$. We survey the main theoretical possibilities and find that only a few simple scenarios can consistently give $N_{\rm eff}=2.81\pm0.12$. One class consists of thermal electrophilic relics with masses $m\sim 8\!-\!13\,{\rm MeV}$. Another consists of out-of-equilibrium particles decaying to $e^+e^-$ or $γγ$, with a rather particular lifetime $0.05\,{\rm s}\lesssim τ\lesssim 3\,{\rm min}$, mass $250\,{\rm MeV}\lesssim m \lesssim 600\,{\rm MeV}$, and abundance $ρ/ρ_γ\sim 0.1$ at decay. Thermal electrophilic particles are especially interesting because they can account for the dark matter in the Universe and can be tested in experiments such as SENSEI, DAMIC-M, and Oscura, and their portals to the visible sector at experiments such as NA64 and LDMX. We conclude that if the Simons Observatory confirms that $N_{\rm eff} \simeq 2.8$, it will point to very specific extensions of the Standard Model.

Neutrino oscillations encode fundamental information about neutrino masses and mixing parameters, offering a unique window into physics beyond the Standard Model. Estimating these parameters from oscillation probability maps is, however, computationally challenging due to the maps' high dimensionality and nonlinear dependence on the underlying physics. Traditional inference methods, such as likelihood-based or Monte Carlo sampling approaches, require extensive simulations to explore the parameter space, creating major bottlenecks for large-scale analyses. In this work, we introduce a data-driven framework that reformulates atmospheric neutrino oscillation parameter inference as a supervised regression task over structured oscillation maps. We propose a hierarchical transformer architecture that explicitly models the two-dimensional structure of these maps, capturing angular dependencies at fixed energies and global correlations across the energy spectrum. To improve physical consistency, the model is trained using a surrogate simulation constraint that enforces agreement between the predicted parameters and the reconstructed oscillation patterns. Furthermore, we introduce a neural network-based uncertainty quantification mechanism that produces distribution-free prediction intervals with formal coverage guarantees. Experiments on simulated oscillation maps under Earth-matter conditions demonstrate that the proposed method is comparable to a Markov Chain Monte Carlo baseline in estimation accuracy, with substantial improvements in computational cost (around 240$\times$ fewer FLOPs and 33$\times$ faster in average processing time). Moreover, the conformally calibrated prediction intervals remain narrow while achieving the target nominal coverage of 90%, confirming both the reliability and efficiency of our approach.

The recent low-energy electron recoil (ER) results reported by the LUX-ZEPLIN (LZ) experiment have established the most stringent constraints to date on new physics scenarios, specifically for solar axion-like particles with keV-scale masses and mirror dark matter. Motivated by this enhanced sensitivity and the resulting restrictive limits, our present work focuses on probing light mediator models via elastic neutrino-electron scattering induced by solar neutrinos. We specifically consider two broad classes of new physics scenarios: (i) universal light mediator models consistent with Lorentz invariance, including scalar, vector, and tensor interactions, and (ii) anomaly-free leptophilic $U(1)'$ gauge extensions featuring a new vector mediator associated with the $L_e-L_μ$, $L_e-L_τ$, $L_μ-L_τ$, and $L_e+2L_μ+2L_τ$ symmetries. By incorporating contributions from these interactions into the neutrino-electron scattering cross-section and utilizing the most precise solar neutrino flux predictions, we analyze the latest LZ ER datasets. We report novel constraints on the coupling-mass parameter space for these models. Furthermore, we contextualize our findings by comparing them with established bounds from various laboratory, cosmological, and astrophysical sources. Our analysis demonstrates that LZ data provide significantly improved limits in previously unconstrained regions of the parameter space.

The three-flavor framework of neutrino oscillations successfully explains most experimental results, but persistent anomalies at short- and long-baseline experiments hint at the existence of additional light sterile states. In particular, eV-scale sterile neutrinos are motivated by LSND and MiniBooNE results, while sub-eV sterile states with mass-squared differences at the $10^{-2}$ and $10^{-5}$~eV$^2$ scales have been proposed to address the T2K--NO$ν$A tension and the absence of the expected upturn in the solar neutrino energy spectrum, respectively. Such sterile states are singlets under the Standard Model gauge group and mix only through their admixture with active neutrinos. In this work, we investigate the phenomenology of the $3+2$ scenario, incorporating one eV-scale sterile neutrino together with a sub-eV state, and analyze their impact on absolute-mass related observables: the sum of neutrino masses $Σ$ constrained by cosmology, the effective electron neutrino mass $m_β$ from beta decay, and the effective Majorana mass $m_{ββ}$ probed in neutrinoless double beta decay. We demonstrate that the presence of two sterile states can significantly modify the allowed parameter space compared to the three-flavor and $3+1$ frameworks, with some mass-ordering schemes already disfavored by current cosmological and laboratory limits. Finally, we assess the implications of upcoming sensitivities from KATRIN, Project~8, and LEGEND-1000, highlighting the complementary role of sub-eV sterile neutrinos in probing physics beyond the minimal three-flavor paradigm.

The determination of the neutrino mass ordering is one of the flagship goals in particle physics. A well-known and powerful synergy emerges when combining high-precision measurements of the effective atmospheric mass-squared splitting from electron antineutrino disappearance in reactor experiments with that from muon (anti)neutrino disappearance in accelerator-based long-baseline experiments. To fully exploit this synergy, percent-level precision in the atmospheric mass splitting is required-a target that JUNO is expected to achieve within a few months of data taking. This motivated the formulation of a mass ordering sum rule for neutrino disappearance channels, which shows that by combining data from T2K and NOvA with JUNO after one year of operation, the neutrino mass ordering can be determined at the $3σ$ confidence level. Since JUNO has recently started taking data, it is timely to ask whether this sum rule remains robust in the presence of new physics. We identify the necessary conditions for new physics to affect the sum rule and demonstrate that, in some cases, such effects could lead to an incorrect inference of the mass ordering. As concrete examples, we consider Scalar Non-Standard Interactions (SNSI) and neutrinos coupled to an ultralight scalar field. We find that, for SNSI, current constraints render any modification of the sum rule negligible, whereas in the latter case, the inference of the ordering requires caution. Nevertheless, these effects can be disentangled, illustrating how the sum rule can also be used to search for new physics.

We explore the interpretation that the diffuse astrophysical neutrino flux is dominated by a single standard candle-like source class. Since recent observations favor a broken power law with a spectral break around 30 TeV, we postulate that the $pγ$ channel is the dominant neutrino production process creating a peak at these energies. We use a SOPHIA-based photo-pion interaction model with a thermal target including high-energy processes, such as multi-pion production, which turns out to be relevant for the interpretation. We demonstrate that target photon temperatures 0.1 to 1 keV are preferred in a multi-parameter fit, whereas the maximal neutrino energies can be limited by A) soft injection spectra, B) a maximal proton energy in the PeV range, or C) magnetic field effects on the secondary muons, pions, and kaons with B in the few 10 kG range. We predict that future measurements, such as of the neutrino flavor composition or neutrino-antineutrino ratio (Glashow resonance), can discriminate scenarios. We also point out that the parameters obtained in our generic approach, such as in the strong magnetic field values, might be indicative for an AGN core origin as a driver of the diffuse flux.

We show that the process of Coherent Elastic neutrino (v) Nucleus Scattering (CEvNS) at nuclear reactor experiments has significant sensitivity to the so-called X17 particle, which has been invoked to explain the ATOMKI anomaly, wherein electron-positron pairs emerging from a nuclear transition of excited Be-8, He-4 and C-12 nuclei are studied. Such a new state has potentially been identified as a spin-1 object, with axial-vector couplings and a mass around 16.7 MeV, hence, in the kinematic range accessible by the aforementioned experimental settings. Specifically, we fit CONUS+ and Dresden-II data and show that a robust statistical analysis renders these more compatible with the X17 hypothesis, in turn interfering with the Standard Model, than with that of the latter alone. The same stays true when also adding COHERENT data from pi+ decays at rest, singling out two regions of preferred couplings of the X17 to electron and muon neutrinos as well as nuclei.

The observation of high-energy neutrinos from the direction of the nearby active galaxy, NGC 1068, was a major step in identifying the origin of high-energy cosmic neutrinos. The multimessenger data imply that high-energy neutrinos originate from the hearts of active galaxies which are opaque to GeV-TeV $γ$-rays. This realization is reinforced by the excess of neutrinos in the direction of NGC 4151 and Circinus Galaxy, other nearby active galactic nuclei (AGNs). Understanding the vicinity of supermassive black holes with electromagnetic radiation is often challenging due to uncertainties associated with the absorption of emission in these dense environments, and neutrinos can be used as a powerful probe of the inner parts of the active galaxies. Considering the five brightest neutrino-active galaxies, NGC 1068, NGC 4151, CGCG 420-15, Circinus Galaxy, and NGC 7469, we employ the measured neutrino spectra together with the sub-GeV $γ$-ray emission measured by the {\em Fermi} satellite to break the degeneracy and narrow in on the parameter space of neutrino emission from turbulent coronae of AGNs. We also study contributions of jet-quiet AGNs, whose properties are similar to NGC 1068 and NGC 7469, to the isotropic neutrino background flux, through exploring possibilities that the neutrino luminosity function may deviate from the X-ray luminosity function. Our results will help estimate the prospects for identifying additional neutrino-active galaxies and guide future targeted analyses.

Observing neutrinoless double beta decay would establish lepton number violation and the Majorana nature of neutrinos. Within the standard 3-flavour paradigm, the rate of this process is controlled by the effective Majorana mass $|\langle m \rangle|$, which may be severely suppressed if the neutrino mass spectrum presents normal ordering. Taking into account the first JUNO results, which significantly reduce the uncertainties on solar neutrino oscillation parameters, we provide updated conditions under which $|\langle m \rangle|_\text{NO}$ is guaranteed to exceed the $10^{-3}$ eV ($5\times 10^{-3}$ eV) threshold. We analyse both the generic case, as well as scenarios where the two Majorana phases either take CP conserving values, or at least one of them takes a CP-violating value, that are in line with predictive schemes combining flavour and generalised CP symmetries.

In short-baseline experiments such as LSND and MiniBooNE, an excess of electron neutrinos has been observed, originating from a muon neutrino beam. To address this anomaly, in the line of many works, we investigate various neutrino mixing schemes involving eV-scale sterile neutrinos alongside three active neutrinos. Using updated experimental and global fit data, we studied neutrinoless double beta decay for three different schemes such as 3+1, 1 + 3, and 2 + 2, which involve one sterile neutrino and three active neutrinos. We have done analysis of these schemes for normal hierarchy (NH) as well as for inverted hierarchy (IH) frameworks, and constrained the sterile neutrino mass in light of current and future neutrinoless double beta decay experiments. The 3+1 scheme is found to be the most viable and at the level of $3σ$ the mass of sterile neutrino with respect to the lightest neutrino mass ($m_{\text{lightest}}$) is restricted to $4.75~eV$ for the NH and $4.72~eV$ for the IH. Additionally, the limits on the sum of four neutrino masses are determined to be $4.81~eV$ for the normal hierarchy and $4.78~eV$ for the inverted hierarchy. The updated analysis of all these schemes would help us in understanding physics governing neutrinoless double beta decay and limit on the mass of sterile neutrinos.

Coherent elastic neutrino-nucleus scattering (CE$ν$NS) is predominantly governed by vector neutral-current interactions, with subleading contributions arising from the axial current in nuclei with non-zero ground-state spin. Experimentally, the extraction of axial-current contributions has been so far of little interest, mainly because of the challenges its measurement entail. In this work, we investigate the relative size of the vector and axial components for target materials currently employed by the neutrino and dark matter experimental communities. We identify fluorine-based compounds as the most promising targets for probing the axial-current event rate. Among them, octafluoropropane ($\text{C}_3\text{F}_8$) emerges as a particularly suitable candidate, given its widespread use in spin-dependent dark matter searches and its relevance for upcoming dedicated CE$ν$NS experiments. Considering both pion decay-at-rest and reactor neutrino fluxes, we show that such measurements can allow an indirect determination of the axial coupling at the $\sim 10\%$ level, depending on flux uncertainties and detector thresholds. We further emphasize that measurements of the axial current will allow to probe spin-dependent new physics scenarios through CE$ν$NS.

Leptogenesis from low-energy CP violation provides a vital link between neutrino physics and the observed baryon asymmetry of the universe. However, this connection is typically obscured by unknown high-energy parameters. In this work, we investigate thermal leptogenesis in the Minimal Left-Right Symmetric Model with generalized parity as the left-right symmetry, where the hermiticity of the Dirac neutrino coupling allows the right-handed mixing matrix $V_\mathrm{R}$ to be determined with minimal assumptions. We show that for a real $V_\mathrm{R}$, these conditions favor CP-conserving Majorana phases, leaving the Dirac CP-violating phase ($δ$) as the sole source of asymmetry. By numerically exploring all four leptogenesis scenarios, we demonstrate that $δ$ alone can generate the observed baryon asymmetry with the correct sign within specific regions of the parameter space. The results exhibit a high sensitivity to the neutrino mass ordering and the lightest neutrino mass, providing a stringent, testable framework for future experimental measurements of the CP phase and neutrino mass scale.

We examine decoherence in neutrino oscillations induced by an ultralight scalar field coupled to neutrinos. The scalar induces time- and position-dependent shifts in the neutrino mass matrix. Neutrinos sample different field configurations throughout an experimental data-taking period, which leads to damping effects in the oscillation pattern in the form of decoherence. By recasting the neutrino-scalar dynamics within the open quantum systems framework, we establish a mapping between a complete model and phenomenological decoherence approaches. We find that the parameter driving decoherence scales as $L^2/E^2$, where $L$ is the baseline and $E$ is the neutrino energy, as opposed to $L/E$ typically assumed in phenomenological studies of open system approaches to neutrino oscillations.

The flavour composition of a future supernova neutrino signal is expected to carry measurable imprints of flavour conversion processes in the dense stellar medium. In this work, we analyse the sensitivity of the upcoming Deep Underground Neutrino Experiment (DUNE) to three phenomenologically distinct effects: slow energy-dependent collective oscillations, fast energy-independent collective oscillations, and standard MSW conversions. By integrating GLoBES and MultiNest and using benchmark neutrino fluxes at emission, we assess the potential of DUNE to extract the underlying flux parameters and discriminate among conversion scenarios.

The distribution of heat-producing elements (U, Th, K) within the Moon is critical for understanding its thermal evolution and formation history. Based on a refined lunar interior model, we calculate the geoneutrino fluxes at two representative detector locations that bracket the expected signal intensity. The maximum flux is found to be slightly lower than the corresponding predicted fluxes for the KamLAND site on Earth, while the minimum flux is approximately a factor of 8.63 lower than this maximum value. The angular distributions of geoneutrinos arriving at the two locations were further computed. Finally, we evaluate the detection prospects for lunar geoneutrinos using three reaction channels: inverse beta decay reaction, elastic scattering on electrons, and a novel radiochemical approach based on $\barν_e + ^3$He $\to e^+ + ^3$H. For each reaction, we calculate the expected event rates and briefly discuss the potential for measuring the total geoneutrino flux, as well as the relative contributions from U, Th, and K.

We compare the sensitivity of the upcoming long-baseline neutrino experiments Protvino to Super-ORCA (P2SO) and the Deep Underground Neutrino Experiment (DUNE) to non-unitarity (NU) of the leptonic mixing matrix in a model-independent framework. NU can arise in theories beyond the Standard Model that include heavy neutral leptons. These effects can modify neutrino oscillation probabilities and introduce new sources of CP violation, which may affect precision measurements of neutrino parameters. We find that DUNE provides stronger bounds on $α_{11}$ and $|α_{21}|$, while P2SO shows better sensitivity to $α_{22}$ and $α_{33}$, mainly due to its longer baseline and stronger matter effects. Our results show that DUNE (P2SO) will be able to improve the current bounds of $α_{11}$ ($α_{33}$). We further examine correlations with standard oscillation parameters and quantify the impact of NU on mass hierarchy, octant, and CP-violation sensitivities. Our results show that these sensitivities depend upon NU in a non-trivial way interconnecting the parameter degeneracies and matter effects. Our results demonstrate the complementarity of P2SO and DUNE in probing NU and show that NU can significantly influence next-generation precision oscillation studies.

The recent observation of coherent elastic neutrino-nucleus scattering from solar $^8$B neutrinos in dark matter direct detection experiments has inaugurated the \emph{neutrino fog} era, highlighting the extended potential of these experiments as precision neutrino observatories. Recent measurements by the XENONnT, PandaX-4T, and LUX-ZEPLIN experiments provide new opportunities to test Standard Model predictions and to probe physics beyond it, in complementarity with dedicated neutrino facilities. We perform a combined analysis of nuclear recoil data from these three facilities to extract information on the solar $^8$B neutrino flux normalization and on the weak mixing angle at low-momentum transfer. We further investigate the impact of new vector interactions on the solar neutrino event rate, deriving constraints on nonstandard neutrino interactions and on scenarios with light vector mediators. Our results demonstrate that dark matter detectors are rapidly becoming complementary to terrestrial neutrino experiments in probing neutrino interactions, and already set competitive bounds on both light and heavy vector mediators.

Measurements of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) neutrino mixing parameters have entered a precision era, enabling increasingly stringent tests of neutrino oscillations. Within the framework of quantum estimation theory, we investigate whether flavor measurements, the only observables currently accessible experimentally, are optimal for extracting the oscillation parameters. We compute the Quantum Fisher Information (QFI) and the classical Fisher Information (FI) associated with ideal flavor projections for all oscillation parameters, considering accelerator muon (anti)neutrino and reactor electron antineutrino beams propagating in vacuum. Two main results emerge. First, flavor measurements saturate the QFI at the first oscillation maximum for $θ_{13}$, $θ_{23}$, and $θ_{12}$, demonstrating their information-theoretic optimality for these parameters. In contrast, they are far from optimal for $δ_{CP}$. In particular, only a small fraction of the available information on $δ_{CP}$ is extracted at the first maximum; the sensitivity improves at the second maximum, in line with the strategy of ESS$ν$SB, a planned facility. Second, the QFI associated with $δ_{CP}$ is approximately one order of magnitude smaller than that of the mixing angles, indicating that the neutrino state intrinsically encodes less information about CP violation. Nevertheless, this quantum bound lies well below current experimental uncertainties, implying that the present precision on $δ_{CP}$ is not fundamentally limited. Our results provide a quantitative framework to disentangle fundamental from practical limitations and establish a benchmark for optimizing future neutrino facilities.

Searches for Lorentz invariance violation (LIV) in the neutrino sector have traditionally focused on non-standard neutrino oscillations induced by LIV in vacuum. In this work, however, we study anisotropic LIV in matter. First, we review vacuum LIV phenomenology, explaining the energy and direction dependence of sidereal modulations for anisotropic coefficients in the Standard Model Extension. We then demonstrate that for high-energy neutrinos, the interplay between anisotropic LIV operators and the Earth's matter potential produces, distinct, observable signatures absent in the vacuum case. We identify a crossover regime where the energy-dependent LIV Hamiltonian becomes comparable to the matter potential, leading to strong interference effects. By analyzing the propagation of neutrinos through a realistic Earth model, we establish three key phenomenological consequences: (1) direction-dependent resonant enhancements of oscillation probabilities, (2) a macroscopic breakdown of neutrino-antineutrino symmetry for CPT-even operators, and (3) a significant increase of the $ν_τ$ flux due to LIV-driven injection of high-energy neutrinos into the $τ$ regeneration cycle. These results highlight that accounting for the interplay between LIV and matter is essential for future LIV searches at large-scale neutrino telescopes.

High-energy neutrinos provide a potentially powerful and distinctive probe for dark matter (DM) - neutrino interactions, particularly in environments with enhanced DM densities, such as the DM spikes predicted to form around supermassive black holes (SMBHs) at the center of active galactic nuclei (AGN). Recent observations by the IceCube Neutrino Observatory, which identified four AGN, namely TXS 0506+056, NGC 1068, PKS 1424+240, and NGC 4151 as neutrino sources, provide a unique opportunity to search for signatures of these interactions. In this study, we use IceCube data to derive the most stringent constraints to date on both the energy-dependent and energy-independent DM-neutrino scattering cross-sections. We perform a statistical analysis using data from individual sources as well as a combined (stacked) analysis of all four sources. Our strongest limits arise from the stacking analysis, yielding an upper bound of $σ_{0} \lesssim 8\times 10^{-39}$ cm$^2$ for an energy-independent cross-section and $σ_{0} \lesssim 10^{-39}$ cm$^2$ for a linearly energy-dependent cross-section, both at 90\% confidence level, particularly in scenarios involving the adiabatic growth of black holes.

The detection of high-energy neutrinos from NGC 1068 and TXS-0506+56 suggests that active galactic nuclei (AGN) may contribute significantly to the the diffuse neutrino flux measured by IceCube. Using 10 years of publicly available IceCube data, we performed a systematic population analysis of X-ray-bright and gamma-ray-bright AGN to evaluate the extent to which this diffuse flux could originate from these sources. We find that gamma-ray-bright blazars can account for no more than 16\% of IceCube's total diffuse flux. Although we find no evidence of neutrino emission from gamma-ray-bright, non-blazar AGN, we cannot exclude the possibility that these sources contribute significantly to the diffuse flux. In contrast, we report (pre-trials) evidence of neutrino emission from several nearby, X-ray-bright, Seyfert-type AGN, including \mbox{NGC 1068} ($4.9σ$), SWIFT J1041.4-1740 ($2.6σ$), SWIFT J0202.4+6824A/B ($2.6σ$), SWIFT J0744.0+2914 (2.6$σ$), NGC 4151 ($2.5σ$), and NGC 3079 ($2.5σ$). Although not fully conclusive, these results suggest that IceCube may be detecting neutrinos from a larger population of Seyfert galaxies. The fact that these sources are not gamma-ray bright indicates that their neutrino production must be taking place in optically thick environments, such as in the coronae surrounding these galaxies' supermassive black holes. We also identify a $4.2σ$ correlation between the neutrinos detected by IceCube and members of the Swift-BAT catalog of X-ray-bright AGN, although this correlation is dominated by NGC 1068. We estimate that this class of sources contributes between 11.2\% and the entirety of IceCube's total diffuse neutrino flux. These results strengthen the emerging case for the prevalence of gamma-ray-obscured AGN as significant sources of high-energy neutrinos.

Thanks to a number of neutrino oscillation and Coherent Elastic neutrino Nucleus Scattering (CE$ν$NS) experiments, the vector Non-Standard Interactions (NSI) of neutrinos have been well studied and constrained. We show that the long-sought-after new physics may hide in the ``axial" non-standard interactions rather than in the vector NSI. We then show how by studying neutral current scattering events in the detectors of long baseline experiments, MINOS, MINOS$+$ and DUNE, the impact of the axial NSI can be discovered.

The ``Practical Dirac-Majorana Confusion Theorem'' (PDMCT) asserts that phenomenological differences between Dirac and Majorana neutrinos are suppressed by $(m_ν/E)^2$ in lepton-number-conserving processes, such that at high energy, it is impossible to experimentally distinguish between Dirac o Majorana neutrinos. In this work, we propose a generalization of this theorem by introducing a New Physics vector boson ($Z'$) with CP-violating, flavor-changing neutral current (FCNC) couplings. While Fermi-Dirac statistics dictate that the flavor-diagonal vector current identically vanishes for Majorana neutrinos, we demonstrate that for non-diagonal transitions, the Majorana condition exactly cancels the real (CP-conserving) component of the vector interaction but keeping only the imaginary part induced by CP violation. Consequently, the kinematic mass suppression is lifted, and the difference in inclusive scattering cross-sections between Dirac and Majorana neutrinos becomes directly dependent on the FCNC CP-violating phase $φ$. We apply this result to Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS), showing that for spin-zero targets, the distinguishability of the neutrino's nature is determined by the CP structure of the new interaction.

Violations of classicality can be probed through measurements performed on a system at different times, as proposed by Leggett and Garg. Specifically, violations of Leggett-Garg inequalities suggest the presence of quantum effects in macroscopic systems. Long-baseline neutrino experiments provide some of the longest available propagation distances over which such tests can be performed. Previous studies of Leggett-Garg tests in the neutrino sector have largely focused on showing that the oscillation probabilities can violate classical bounds for certain parameter choices. In this work, we develop a more complete and data-driven framework that treats both the distributions representing the classical and quantum behavior, as well as the experimental uncertainties. We consider MINOS, T2K, NOvA, as well as the upcoming DUNE, and present the respective statistical significance for distinguishing quantum behavior from classical scenarios at these long-baseline neutrino experiments. Among them, we find that T2K yields the most significant violation of classicality, at the level of $\sim 14 σ$, with NOvA and projections for DUNE also resulting in a significance of more than $5σ$.

First results from the JUNO reactor neutrino experiment already determine with world-leading precision the small neutrino squared-mass splitting $Δm^2_{21}$ and the mixing angle $θ_{12}$. In this article we perform an exploratory study beyond these, taking advantage of the first JUNO data release to discuss its sensitivity to the large squared-mass splitting, $Δm^2_{3\ell}$. When combined with constraints from global oscillation data, this may already contain some information on the neutrino mass ordering. Indeed, we find that the combination of the complementary $Δm^2_{3\ell}$-determinations gives a slight preference for Normal Ordering, with a p-value for Inverted Ordering of 2%-2.6% ($2.2σ$-$2.3σ$). We study the robustness of this result with respect to potential systematic uncertainties and statistical fluctuations. Taken at face value, a full global analysis of oscillation data including the publicly available JUNO information and data leads to a preference for Normal Ordering with $Δχ^2 = 4.6$ and 9.4 without and with Super-K and IceCube-24 atmospheric neutrino data, respectively.

The cosmic neutrino background (C$ν$B) can be boosted to high energies due to scatterings with energetic cosmic rays (CRs) across cosmological scales. Previous calculations focused on neutral current incoherent and coherent elastic scatterings of cosmic-ray protons off relic neutrinos. However, charged current interactions and deep inelastic scatterings are also expected to occur, which enhances the boosted relic neutrino fluxes on Earth. Here, we compute the \textit{total} diffuse boosted cosmic neutrino background (DBC$ν$B) arising from CRs at all redshifts in the Universe, accounting for neutral current and charged current elastic and deep inelastic scatterings. We find that IceCube already places an upper limit on the cosmic neutrino background overdensity in cosmological scales of ~$\mathcal{O}(100-1000)$ at $E_ν=10^{10}$ GeV, for a lightest neutrino mass of $m_ν \gtrsim 0.1$ eV. We further show that IceCube-Gen2 could test $\mathcal{O}(1-10)$ C$ν$B overdensities, and the combination of $10$ future neutrino telescopes with similar sensitivity would allow us to test the $Λ$CDM expected C$ν$B density for a lightest neutrino mass compatible with the KATRIN bound.

In this paper, we present an improved test of $CPT$ symmetry in the neutrino sector by analyzing the atmospheric mass-squared splittings, $Δm^2_{31}$ and $Δ\overline{m}^2_{31}$, using on-going JUNO and future DUNE and Hyper-Kamiokande experiments. Our study focuses on the discrepancy $δ_{ν\overlineν}(Δm^2_{31}) = Δm^2_{31} - Δ\overline{m}^2_{31}$, achieving unprecedented precision by exploiting the high statistics and reduced systematic uncertainties of these facilities. The combined analysis yields a sensitivity to $CPT$ violation at the level of $2\times 10^{-5}~\text{eV}^2$ at $3σ$ confidence level, representing a $60\%$ improvement over the joint T2K-NO$ν$A-JUNO analysis. These results highlight the crucial role of multi-experiment synergies in testing fundamental symmetries of nature.

In this work, we study leptonic decays of hadrons as probes of light neutrinophilic scalars that mediate enhanced neutrino self-interactions. Such scalars can be emitted in processes involving neutrinos, turning two-body decays into three-body final states and producing characteristic spectral distortions. We compute these effects for charged pion decay and nuclear electron capture decay, including both on-shell and off-shell scalar emission, as well as the loop-induced renormalization required to cancel divergences. Using these results, we derive the projected sensitivity of PIONEER and assess the current and future reach of BeEST. The resulting low-energy spectral tails provide a characteristic signal for light neutrinophilic scalars, making upcoming hadron decay experiments powerful probes of light mediators of non-standard neutrino self-interactions.

We investigate the possibility of neutrinos interacting with a scalar dark matter field and the resulting implications for neutrino oscillations in the long-baseline sector. As our Universe is predominantly composed of dark matter, neutrinos propagating over astrophysical and terrestrial baselines inevitably traverse a dark matter background. The coherent forward scattering of neutrinos in such a background induces a medium-dependent correction to the mass-squared term in the effective neutrino Hamiltonian having opposing signs for neutrinos and antineutrinos. We study how the elements of this correction matrix, arising from coherent forward scattering of neutrinos with scalar dark matter background referred to as dark non-standard interactions (dark NSI), modify neutrino oscillation probabilities. Furthermore, we also study the effect of the off-diagonal elements and the associated phases on the measurement of leptonic CP violating phase focusing on the upcoming long-baseline superbeam experiments DUNE and T2HK. We show that dark NSI can lead to substantial enhancement or suppression of CP-violation sensitivity, depending on the true values of the dark NSI phases $φ_{αβ}$. We further explored how the synergy of DUNE and T2HK can effectively mitigate the degeneracies due to the dark NSI phases, and can restore or even enhance the CP sensitivity as compared to the standard oscillation scenario.

A new tension is emerging between the tight cosmological upper bounds on the total neutrino mass ($\sum m_ν\lesssim 0.06 \, \rm{eV}$) and the lower limits from oscillation experiments, with potentially far-reaching implications for cosmology and particle physics. Neutrinos decaying into massless BSM particles with lifetimes $τ_ν\sim 0.01-1\, \rm{Gyr}$ represent a theoretically well-motivated mechanism to reconcile such measurements. Using DESI DR2 and CMB datasets, we show that such decays relax the bound on the total neutrino mass up to $\sum m_ν< 0.23 \, \rm{eV}$ (95%), restoring full agreement with oscillation data. We also present the first late-time cosmological analysis of neutrino decays into lighter neutrinos in a manner consistent with the measured mass splittings. In contrast to the decays into massless BSM particles, we find that this scenario only marginally alleviates - or even tightens - the cosmological neutrino mass bounds, depending on the mass ordering.

Right-handed neutrinos are naturally induced by dark extra dimension models and play an essential role in neutrino oscillations. The model parameters can be examined by the long-baseline neutrino oscillation experiments. In this work, we compute the predicted neutrino oscillation spectra within/without extra dimension models and compare them with the experimental data. We find that the neutrino data in the T2K and NOvA experiments are compatible with the standard neutrino oscillation hypothesis. The results set the stringent exclusion limit on the extra dimension model parameters at a high confidence level. The derived constraints on dark dimension right-handed neutrinos are complementary to those results from the collider experiments and cosmological observations.

For over thirty years, a $\sim20\%$ deficit, now exceeding $5σ$, has persisted between measured and predicted neutrino capture rates on $^{71}$Ga, as observed in radioactive source experiments (namely GALLEX, SAGE, and more recently BEST) using $^{51}$Cr and $^{37}$Ar. This long-standing discrepancy, referred to as the gallium anomaly, has posed a significant challenge to our understanding of both experimental methods and theoretical predictions. In this work, we revisit the theoretical calculation of the neutrino capture cross-section by moving beyond the standard treatment of the leptonic wave functions, revealing limitations in the commonly used factorization approach based on the detailed balance principle. Incorporating phenomenologically constrained Gamow-Teller transition densities, able to correctly reproduce the precisely measured half-life of $^{71}{\textrm{Ge}}$, we find that the revised cross-section can be significantly reduced, potentially resolving the gallium anomaly without invoking new physics.

We use the Caley-Hamilton theorem to derive analytical solutions for the three-flavor neutrino propagation amplitude in a constant-density medium and their derivatives with respect to the mixing parameters. This approach avoids the diagonalization of the Hamiltonian and exploits precomputed matrix invariants to separate the dependence of oscillation probabilities on neutrino energy and propagation baseline. The results are implemented in the CHIC software, which provides simple, fast and efficient computation of oscillation probabilities and their derivatives. Finally, we demonstrate the value of probability gradients for neutrino data analyses and introduce a complementary visualization, the oscillograds, to probe underlying features of neutrino mixing.

Matter-induced neutrino flavor mixing (the Mikheyev-Smirnov-Wolfenstein, or MSW, effect) is a central prediction of the neutrino mixing framework, but it has not been conclusively observed. Direct observation of the energy-dependent MSW transition in the solar electron-neutrino survival probability would solve this, but backgrounds have been prohibitive. We show that our new technique for suppressing muon-induced spallation backgrounds will allow JUNO to measure the MSW transition at $>$4$σ$ significance in 10 years. This would strongly support upcoming multi-\$1B next-generation long-baseline experiments and their goals in cementing the neutrino mixing framework.

We explore the potential of the Jiangmen Underground Neutrino Observatory (JUNO) to probe new physics by searching for Lorentz-invariance violation (LIV). Using the 59.1-day dataset recently released by this experiment, we analyze neutrino oscillations to place new constraints on the LIV parameters in the CPT-even ($c_{ee} - c_{eμ}$, $c_{ee} - c_{eτ}$) and CPT-odd ($a_{ee} - a_{eμ}$, $a_{ee} - a_{eτ}$) sectors. Our analysis reveals a significant shift in the oscillation parameter space of $\sin^2θ_{12}-Δm^2_{21}$ when LIV is included; with the best-fit point for normal ordering moving to the higher values of the solar angle $θ_{12}$, a strong preference emerges for inverted mass ordering. In particular, the $c_{ee} - c_{eτ}$ and $a_{ee} - a_{eτ}$ sectors show the most pronounced effects. We report the most stringent bounds from JUNO to date on these LIV parameters, showcasing the detector's unique sensitivity to physics beyond the Standard Model.

The recent observation of high-energy Galactic neutrinos by IceCube allows for searches of new physics affecting neutrino propagation on scales of $O(10^9-10^{15})\,\mathrm{km/GeV}$ in distance over energy. We assess the sensitivity of upcoming measurements of Galactic neutrinos by IceCube and KM3NeT to such new phenomena. We focus on two scenarios: quasi-Dirac neutrinos and neutrino decays. In the quasi-Dirac scenario, we find that joint measurements by IceCube and KM3NeT are sensitive to the mass-squared differences $δm^2 \in \left(10^{-13.5}~\mathrm{eV^2}, 10^{-11.9}~\mathrm{eV^2}\right)$ at the $90\%$ confidence level. For neutrino decays, the same measurements are sensitive to mass over lifetime ratios $m / τ> 10^{-12.3}~\mathrm{eV^2}$ at the same significance. Our results demonstrate that measurements of Galactic neutrinos by a global network of neutrino telescopes can probe signatures of neutrino mass models.

We consider realizations of a gauged B-L symmetry in the context of the Dark Dimension scenario, where the SM lives on a codimension one brane in 5d spacetime. The B-L can naturally be a bulk gauge symmetery leading to a global symmetry on the SM brane, and have its gauge anomaly canceled by charged bulk modes. This naturally leads to the existence of 3 right-handed neutrinos propagating in the dark dimension. Allowing for Higgsing of B-L by a bulk scalar at the Higgs scale, results in a massive gauge field with $m_{B-L}\sim 100$ GeV and weak coupling $g_{B-L}\sim 10^{-10}$ which is allowed by current bounds. The model also predicts a natural matching $m_ν\sim m_{KK}\simΛ^{1/4}$, thereby providing a theoretical explanation for the observed coincidence between neutrino masses and the Dark Energy scale. It also predicts a tower of sterile right-handed neutrinos in the $keV$ mass range.

Coherent elastic neutrino-nucleus scattering (CE$ν$NS) has been experimentally confirmed using neutrinos from pion decay at rest, solar neutrinos and reactor antineutrinos. Future CE$ν$NS experiments will foreseeable lead to precision measurements which will be a powerful tool to search for new physics beyond the Standard Model. In this work, we investigate possible deviations from unitarity in the $3\times3$ leptonic mixing matrix that controls the propagation of active neutrinos. Such deviations may originate from the mixing with additional gauge singlet fermions and depending on their mass scale and mixing, the resulting phenomenology can differ substantially. We explore two well-motivated regimes: the \textit{seesaw limit}, where the new fermions are heavy and kinematically inaccessible, leading to effective deviations from unitarity in the active sector; and the \textit{light sterile limit}, where they are light enough to be produced and participate in neutrino propagation and scattering processes. We show how these scenarios modify both CE$ν$NS and elastic neutrino--electron scattering (E$νe$S), and we present the corresponding sensitivity projections for a future CE$ν$NS reactor experiment obtained by upscaling the CONUS+ experiment, which reported the first observation of reactor CE$ν$NS. We identify the leading experimental systematics relevant for such an upscaling and demonstrate the resulting capability to probe TeV-scale new physics. Our results highlight the strong potential of CE$ν$NS to test the structure of the lepton sector and to search for physics beyond the Standard Model.

Inverse beta decay (IBD), $\overlineν_e p \to e^+ n \left( γ\right)$, is the main detection channel for reactor antineutrinos in water- and hydrocarbon-based detectors. As reactor antineutrino experiments now target sub-percent-level sensitivity to oscillation parameters, a precise theoretical description of IBD, including recoil, weak magnetism, nucleon structure, and radiative corrections, becomes essential. In this work, we give a detailed and precise calculation of the total and differential cross sections for radiative IBD, $\overlineν_e p \to e^+ n γ$. We use a heavy baryon chiral perturbation theory framework, systematically incorporating electroweak, electromagnetic, and strong-interaction corrections. We derive new analytic cross-section expressions, clarify the collinear structure of radiative corrections, and provide a systematic uncertainty analysis. We also discuss phenomenological applications for reactor antineutrino experiments, e.g., JUNO, and neutron decay. Our results enable sub-permille theoretical precision, supporting current and future experiments.

We derive a complete expression for the neutrino-mediated quantum force beyond the four-Fermi approximation within the Standard Model. Using this new result, we study the effect of atomic parity violation caused by neutrinos. We find that the neutrino effect is sizable compared to the current experimental sensitivity and can also significantly affect the value of the Weinberg angle measured in atomic systems. This offers a promising method for detecting the neutrino force in the future and facilitates the application of precision atomic physics as a probe for neutrino physics and the electroweak sector of the Standard Model.

We examine the sensitivity of the ESSnuSB and DUNE long-baseline neutrino experiments to isotropic, CPT-violating Lorentz Invariance Violation (LIV). Using detailed simulations for the 360 km and 540 km ESSnuSB baselines and the 1300 km DUNE setup, we assess how LIV parameters influence oscillation probabilities, event spectra, and degeneracies among oscillation parameters. We find that LIV-induced modifications can closely mimic variations in $θ_{23}$ and $δ_{\rm CP}$, potentially leading to incorrect determination of the atmospheric mixing angle octant and the leptonic CP phase if LIV effects are not accounted for. Although combining the two ESSnuSB baselines improves overall sensitivity, it does not fully remove these degeneracies. In contrast, a joint ESSnuSB+DUNE analysis benefiting from the synergy between second-maximum sensitivity at ESSnuSB and first-maximum, matter-enhanced sensitivity at DUNE can successfully resolve all these degeneracies and can yield significantly stronger constraints on all the LIV parameters. The results presented here highlights the essential role of multi-baseline, multi-energy experimental strategies to probe Planck-suppressed Lorentz-violating new physics.

Working within the reference three-neutrino mixing framework, we confront the lepton mixing predictions derived using non-Abelian discrete flavour and CP symmetries with the first JUNO data on the solar neutrino mixing parameters $\sin^2θ_{12}$ and with the results of the latest global neutrino data analysis. We focus on symmetry breaking patterns for which the lepton PMNS mixing matrix depends only on one or two free real parameters. Performing a comprehensive statistical analysis in each of the considered cases, we report the best fit values, the $3σ$ C.L. allowed ranges and the $χ^2$-distributions of the lepton mixing observables - the three mixing angles and the three CP-violation phases. We find that the JUNO measurements can disfavour or rule out a number of the mixing patterns associated with specific types of breaking of the discrete flavour and CP symmetries. The synergy of JUNO, DUNE and T2HK data can provide an exhaustive test of the considered approach to lepton mixing based on non-Abelian discrete lepton flavour symmetries combined with the CP symmetry.

This paper provides a comprehensive overview of neutrino masses and mixing in Large Extra Dimension scenarios, focusing on the phenomenological impact of a five-dimensional (5D) bulk fermion. In a flat extra dimension compactified on an $S^1/\mathbb{Z}_2$ orbifold, this fermion manifests as a Kaluza-Klein tower of right-handed neutrinos in the 4D effective theory. We systematically investigate four distinct scenarios for mass generation, considering both Dirac and Majorana mass terms originating from either the bulk or the 3-brane. For each case, we analyse the consequences for neutrino oscillations in a vacuum and in matter, deriving the resulting mass spectra and mixing patterns. By comparing these theoretical predictions with experimental data, we explore the constraints on the large extra dimensions' parameters.

Neutrino self-interaction beyond the Standard Model is well motivated by the nonzero masses of neutrinos, which are the only known particles guaranteed to have new physics. Cosmic messengers, especially neutrinos, play a central role in probing new physics, as they provide experimental conditions far beyond the reach of laboratories and serve as the link between laboratory fundamental-physics discoveries and their roles in the Universe, where many new physics motivations originate. In this work, we propose a novel probe of neutrino self-interactions through ultra-high-energy neutrinos scattering off the cosmic neutrino background when the lightest neutrino species remains relativistic today. This allows us to ``Widen the Resonance'' of such scattering. Meanwhile, we also provide a semi-analytic framework for cosmogenic UHE neutrino production, avoiding computationally intensive simulations and yielding results precise enough for BSM studies. The widened resonance enables future ultrahigh-energy neutrino telescopes, in particular GRAND, to probe mediator masses from MeV to GeV, reaching couplings down to $g \sim 10^{-3}$ -- up to two orders of magnitude beyond current bounds. Our results enhance the discovery potential of $ν$SI in the high-mass regime, potentially offering crucial insights into the connections between the neutrino sector and dark sector.

Within the standard $3ν$ framework, we discuss updated bounds on the leading oscillation parameters related to the $(ν_1,\,ν_2)$ states, namely, the squared mass difference $δm^2=m^2_2-m^2_1$ and the mixing parameter $\sin^2θ_{12}$. A previous global analysis of 2024 oscillation data estimated $δm^2$ and $\sin^2θ_{12}$ with fractional $1σ$ errors of about $2.3\%$ and $4.5\%$, respectively. First we update the analysis by applying the latest SNO+ constraints, that slightly shift the $(δm^2,\,\sin^2θ_{12})$ best fits. Then we apply the constraints placed by the first JUNO results, that significantly reduce the uncertainties of both parameters. Our updated global bounds (as of 2025) can be summarized as: $δm^2/10^{-5}{\rm eV}^2 = 7.48\pm 0.10$ and $\sin^2θ_{12}=0.3085\pm0.0073$ (with correlation $ρ=-0.20$), corresponding to $1σ$ uncertainties as small as $1.3\%$ and $2.4\%$, respectively. We also comment on minor physical and statistical effects that, in the future, may contribute to lift the current mass-ordering degeneracy of $(δm^2,\,θ_{12})$ estimates.

The precise measurement of the leptonic CP-violating phase $δ_{CP}$ remains one of the major open challenges in neutrino physics, as current experiments achieve only very limited accuracy. We address this issue through the lens of quantum estimation theory. A distinctive feature of neutrino oscillation experiments is that they cannot freely optimize the probe or measurement, since both are constrained by the production and detection of flavor eigenstates. We therefore examine whether the large uncertainty in $δ_{CP}$ originates from intrinsic reasons, either of the neutrino quantum state or of flavor measurements, or if it instead stems from experimental limitations. By comparing quantum and classical Fisher information, we demonstrate that the limited sensitivity to $δ_{CP}$ originates primarily from the information content of flavor measurements. Furthermore, we show that targeting the second oscillation maximum, as in the ESS$ν$SB proposal, substantially enhances $δ_{CP}$ information compared to experiments centered on the first maximum.

Over the next decade, $\mathcal{O}(100)$ diffuse supernova neutrino background (DSNB) events are expected in Hyper-Kamiokande. Another neutrino source that has received far less attention is binary neutron star mergers. Including the data from recent simulations, we find that detection in current and near-future neutrino experiments is not feasible, and a megaton-scale detector with $\mathcal{O}(10)$ MeV threshold, such as the proposed Deep-TITAND, MEMPHYS, or MICA, will be required. This is due to the updated binary neutron star merger rate and the time-of-flight delay caused by the nonzero neutrino mass. Regarding the former, recent results from LIGO, Virgo, and KAGRA has significantly lowered the upper limit on the neutron star merger rate. As for the latter, neutrino events from neutron star mergers are expected to be recorded shortly after the gravitational wave signal. Limiting the analysis to such short time windows can significantly reduce background rates. While this approach has been qualitatively discussed in the literature, the effect of the time delay caused by neutrino mass, which can substantially extend the observation windows, has been disregarded. We present a refined analysis employing energy-dependent time windows and luminosity distance cuts for the mergers and provide realistic estimates of the detector runtime required to record neutrinos from binary neutron star mergers with small background contamination. The relative timing between the neutrino and gravitational wave signals can also be employed to probe the scale of neutrino mass. We find that the sensitivity to the lightest neutrino mass exceeds both the most stringent terrestrial bounds from KATRIN and the projections based on galactic supernovae. This level of sensitivity may become particularly relevant in the future if terrestrial and supernova constraints are not significantly improved.

The JUNO Collaboration has recently released its first reactor antineutrino oscillation result, achieving unprecedented precision in the measurement of $Δm^2_{21}$ and $\sin^2θ_{12}$. We emphasize that the accurate determination and modeling of the terrestrial matter density profile are fundamental for extracting the oscillation parameters and probing the neutrino mass ordering. This paper presents a realistic piecewise-constant model for the shallow crustal density profile along the baselines from Taishan and Yangjiang to the experimental hall, based on geological and petrophysical information. The uncertainty in the density profiles arises from variations in the density and length of each segment, both of which are conservatively estimated to be 10%. A careful comparison of constant and fluctuated density profiles is provided and the implications for the precision measurement of oscillation parameters are discussed. Finally, we also discuss the prospect of shallow crust tomography in future reactor neutrino experiments.

The first results from the JUNO reactor neutrino oscillation experiment improve our knowledge of neutrino masses and mixing parameters, especially the solar angle $θ_s \equiv θ_{12}$ and the solar mass squared difference $Δm^2_s \equiv Δm^2_{21}$. We discuss the implications of these results on neutrinoless double beta decay by itself and in combination with the global fit of neutrino oscillation experiments, the JUNO first data, and cosmological constraints on the neutrino mass sum. For the effective mass $\langle m_{ee} \rangle$, the uncertainties in its lower limits for both mass orderings and upper limits for the normal ordering are largely reduced. Since the cosmological CMB and DESI BAO data put a stringent constraint on the neutrino mass scale, we also show how the probability distribution of both the real and imaginary parts of the effective mass $\langle m_{ee} \rangle$ on the complex plane is affected. Especially, the funnel region with $|\langle m_{ee} \rangle| \lesssim 1$\,meV receives larger chance to happen. Correspondingly, the chance of determining the two Majorana CP phases simultaneously in this region also increases with reduced uncertainty.

We derive general formulas for three flavor fractions $(η^{}_e , η^{}_μ, η^{}_τ)$ of the high-energy neutrinos originating from a remote astrophysical source by using their flavor ratios $(f^{}_e , f^{}_μ, f^{}_τ)$ observed at a neutrino telescope, and diagnose a potential divergence associated with $η^{}_μ$ and $η^{}_τ$ as an unavoidable consequence of the $μ$-$τ$ interchange symmetry exhibiting in the $3\times 3$ lepton flavor mixing matrix $U$. We present a complete set of analytical expressions for $(η^{}_e , η^{}_μ, η^{}_τ)$ as functions of two typical $μ$-$τ$ symmetry breaking parameters in the standard parametrization of $U$, and apply it to the recent IceCube all-sky neutrino flux data ranging from 5 TeV to 10 PeV in the assumption that the relevant sources have a common flavor composition. We also explain why only $η^{}_e$ and $η^{}_μ+ η^{}_τ$ can be extracted from a precision measurement of $f^{}_e$ and $f^{}_μ= f^{}_τ$ in the exact $μ$-$τ$ flavor symmetry limit.

Precise neutrino energy reconstruction is essential for next-generation long-baseline oscillation experiments, yet current methods remain limited by large uncertainties in neutrino-nucleus interaction modeling. Even so, it is well established that different interaction channels produce systematically varying amounts of missing energy and therefore yield different reconstruction performance--information that standard calorimetric approaches do not exploit. We introduce a strategy that incorporates this structure by classifying events according to their underlying interaction type prior to energy reconstruction. Using supervised machine-learning techniques trained on labeled generator events, we leverage intrinsic kinematic differences among quasi-elastic scattering, meson-exchange current, resonance production, and deep-inelastic scattering processes. A cross-generator testing framework demonstrates that this classification approach is robust to microphysics mismodeling and, when applied to a simulated DUNE $ν_μ$ disappearance analysis, yields improved accuracy and sensitivity. These results highlight a practical path toward reducing reconstruction-driven systematics in future oscillation measurements.

The SNO+ Collaboration reports new results on reactor antineutrino oscillations using data acquired from May 2022 through July 2025. The spectral analysis of a flux dominated by nuclear reactors at 240, 350, and 355 kilometers yields the mass-squared difference $Δm^2_{21}=(7.93^{+0.21}_{-0.24})\times 10^{-5}$ eV$^2$. This result is compatible with and approaches the precision of the only other long-baseline reactor antineutrino measurement, by KamLAND. Combining these measurements, along with those from solar neutrino experiments, the global values of the neutrino mixing parameters become: $Δm^2_{21}$ = $(7.63\pm0.17)\times 10^{-5}$ eV$^2$ and $\sin^2{θ_{12}}=0.310\pm0.012$. The analysis of geoneutrinos at SNO+ is also improved, with a measured signal of 49$^{+13}_{-12}$ TNU.

Neutrino oscillation parameters are subject to renormalization group (RG) evolution, just like all couplings and masses of Standard Model (SM) particles. Within the SM extended with three massive neutrinos, it is well known that RG running effects in the neutrino sector are small. However, the RG running of the elements of the leptonic mixing (PMNS) matrix below the electroweak symmetry breaking scale can be enhanced in the presence of light neutrinophilic new particles. In this work, using a particular low-scale neutrino mass model as an example, and by taking into account both atmospheric and astrophysical neutrino fluxes, we show that RG running of the PMNS matrix can lead to an increased number of high-energy tau neutrino events at IceCube. This excess manifests as an increased number of spatially displaced showers called ``double bangs". We find that the number of double bangs induced by new physics through RG effects can be comparable to that arising from SM interactions of astrophysical tau neutrinos.

In this work, we investigate the sensitivity of Hyper-Kamiokande (Hyper-K) to light sterile neutrinos within the $(3+1)$ framework, consisting of three active and one sterile neutrino state. We focus on the regime where the new mass-squared splitting satisfies $Δm_{41}^{2} \lesssim 1$ eV$^{2}$, a parameter space complementary to short-baseline sterile-neutrino searches. Using both accelerator and atmospheric neutrino samples, we evaluate the expected capability of Hyper-K to constrain active-sterile mixing. Our results show that Hyper-K can significantly improve current bounds on sterile-neutrino parameters and achieve sensitivity that is competitive with that of future dedicated experiments.

Algorithms for computing neutrino oscillation probabilities in sharply varying matter potentials such as the Earth are becoming increasingly important. As the next generation of experiments, DUNE and HyperK as well as the IceCube upgrade and KM3NeT, come online, the computational cost for atmospheric and solar neutrinos will continue to increase. To address these issues, we expand upon our previous algorithm for long-baseline calculations to efficiently handle probabilities through the Earth for atmospheric, nighttime solar, and supernova neutrinos. The algorithm is fast, flexible, and accurate. It can handle arbitrary Earth models with two different schemes for varying density profiles. We also provide a c++ implementation of the code called NuFast-Earth along with a detailed user manual. The code intelligently keeps track of repeated calculations and only recalculates what is needed on each successive call which can also help provide significant speed-ups.

Recent analyses combining cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) challenge particle physics constraints on the total neutrino mass, pointing to values smaller than the lower limit from neutrino oscillation experiments. To examine the impact of different CMB likelihoods from $\mathit{Planck}$, lensing potential measurements from $\mathit{Planck}$ and ACT, and BAO data from DESI, we introduce an effective neutrino mass parameter ($\sum \tilde{m}_ν$) which is allowed to take negative values. We investigate its correlation with two extra parameters capturing the impact of gravitational lensing on the CMB: one controlling the smoothing of the peaks of the temperature and polarization power spectra; one rescaling the lensing potential amplitude. In this configuration, we infer $\sum \tilde{m}_ν=-0.018^{+0.085}_{-0.089}~\text{eV}~(68\% ~\text{C.L.})$, which is fully consistent with the minimal value required by neutrino oscillation experiments. We attribute the apparent preference for negative neutrino masses to an excess of gravitational lensing detected by late-time cosmological probes compared to that inferred from $\mathit{Planck}$ CMB angular power spectra. We discuss implications in light of the DESI BAO measurements and the CMB lensing anomaly.

The diffuse emission of gamma-rays and neutrinos, produced by interactions of cosmic rays with interstellar matter in the Milky Way, provides valuable insights into cosmic ray propagation and Galactic processes. Emission models incorporating different assumptions about cosmic ray diffusion, source distribution, and target gas density are tested using data from neutrino telescopes. In this study, the final all-flavor neutrino dataset, collected over 15 years (2007--2022) by the ANTARES neutrino telescope, is analyzed. A maximum likelihood ratio method built to handle templates of Galactic emission models is employed to evaluate the compatibility of these models with the observed spatial and energy distributions of neutrino events. The results do not yield stringent constraints on the tested models and upper limits on the diffuse neutrino flux are derived, which are compatible with the results obtained by other experiments.

In this work, we study the influence of charged-current non-standard interactions (CC-NSI) at a DUNE-like experiment. We are particularly interested in the tau neutrino channel accessible at DUNE, given the higher energy neutrino flux expected to be achieved by the experiment. We focus on CC-NSI that may affect the pion decay, the primary source of neutrinos for DUNE. We show that the expected sensitivity at the near detector may supersede the present bounds coming directly from pion decay by one order of magnitude.

Neutrinos oscillate over cosmic distances. Using 11.4 years of IceCube data, the flavor composition of the all-sky neutrino flux from 5\,TeV--10\,PeV is studied. We report the first measurement down to the $\mathcal{O}$(TeV) scale using events classified into three flavor-dependent morphologies. The best fit flavor ratio is $f_e:f_μ:f_τ\,=\,0.30:0.37:0.33$, consistent with the standard three-flavor neutrino oscillation model. Each fraction is constrained to be $>0$ at $>$ 90\% confidence level, assuming a broken power law for cosmic neutrinos. We infer the flavor composition of cosmic neutrinos at their sources, and find production via neutron decay lies outside the 99\% confidence interval.

The growing evidence for nano-hertz gravitational waves, from NANOGrav and other observations, may be pointing to a cosmological first-order phase transition at temperatures of $\mathcal{O}(10-100)\;\mathrm{MeV}$. Such an interpretation requires dynamics beyond the Standard Model in this energy range. If so, it may well be the case that core-collapse supernova explosions would recreate the first-order phase transition leaving a unique imprint on the spectrum of neutrinos emitted in the initial few seconds. This scenario is also suggestive of a low-mass seesaw mechanism to explain neutrino masses. We outline the prospects for future observations of Galactic supernovae to uncover the signals of this scenario, which could get further confirmation with additional pulsar timing array data establishing the primordial origin of the observed nano-hertz gravitational waves.

In this article, we introduce the concept of \textit{topographic enhancement} in the context of ultra-high-energy neutrino detection by underwater neutrino telescopes. We demonstrate that the local topography around KM3NeT/ARCA can increase the detection efficiency in scenarios involving long-lived particles by up to a factor of $\sim 3$ due to the presence of an underwater mountain range in the direction of Malta. We consider a simplified model-independent approach that parametrizes the new physics able to generate both track-like and cascade-like signals in neutrino telescopes. When explaining the KM3-230213A event with a diffuse dark flux hypothesis, including its azimuthal direction--in addition to the zenith angle--provides additional constraints on the parameter space. In this effective model, the observations by KM3NeT and ANITA-IV can be simultaneously explained and the global tension with the lack of a corresponding detection in IceCube is reduced to 2.4 sigma. This work underscores the importance of incorporating topographic effects in the design and optimization of next-generation neutrino telescopes, as is done in the context of mountain-based detectors such as TAMBO. We present a numerical code which can be used to easily extend this topographical analysis to other experiments.

We conjecture that there exists a remarkable correlation among the three elements in the first row of the $3\times 3$ lepton flavor mixing matrix $U$: $|U^{}_{e1}|^2 = 2 \left(|U^{}_{e2}|^2 + |U^{}_{e3}|^2\right)$, which holds even though $U$ is non-unitary in the canonical seesaw mechanism. This ``first-row correlation" is fully consistent with $\sin^2θ^{}_{12} = \left(1 - 2\tan^2θ^{}_{13}\right)/3$ in the unitarity limit of $U$, as supported by the latest JUNO and Daya Bay precision measurements at a confidence level close to $1σ$.

The Electron-Ion Collider (EIC) is a next-generation accelerator primarily designed to study the internal structure of nucleons through high-precision electron-hadron collisions. In this work, we explore the feasibility of employing a 1 MW fraction of the EIC proton beam to generate a high-intensity GeV-scale neutrino beam for long-baseline oscillation studies. We have simulated proton-target interactions and optimize the resulting neutrino fluxes for water-based liquid scintillator (WbLS) detectors located at distinct baselines of 900 km and 2900 km. Oscillation analyses performed with GLoBES show that extended baselines allow access to multiple oscillation maxima, significantly enhancing sensitivity to leptonic CP violation. The study also examines the interplay between matter effects and the intrinsic CP violating phase in shaping observable asymmetries. We note that simplified systematics and no backgrounds are used in this analysis to establish the baseline physics potential. These results suggest that the EIC proton beam could provide a novel and complementary source for precision neutrino physics, extending the scientific reach of the EIC program.

The anisotropies of the Cosmic Neutrino Background (C$ν$B) offer an ideal tool to test non-standard neutrino interactions, since they directly trace the perturbations in the neutrino distribution function. Here, we study how invisible neutrino decays impact the C$ν$B anisotropies, in a framework where neutrinos decay non-relativistically to dark radiation and lighter neutrinos in a manner consistent with the measured mass splittings. For this purpose, we perform the first implementation of such a late-time neutrino decay scenario within a linear Einstein-Boltzmann solver, and compute the C$ν$B angular power spectra from the Boltzmann hierarchy solutions for a range of lifetimes and decay channels. We find that neutrino decays leave very strong signatures on the C$ν$B angular spectra, about two orders of magnitude larger than on the CMB angular spectra, particularly for lifetimes comparable to the age of the Universe. We show that a future polarized tritium target run of the PTOLEMY experiment, with sufficient counting statistics to measure just the first $\sim 15$ multipoles of the neutrino sky map, could test neutrino decay models that remain undetectable with CMB data.

New, neutrinophilic mediators are one potential extension beyond the Standard Model of particle physics. Often, studies of neutrinophilic mediator consist of searching for direct evidence of its production and/or its tree-level virtual effect for generating strong neutrino self-interaction. In this work, we focus instead on the fact that such new mediators \textit{also} lead to deviations in neutrino-matter scattering via radiative corrections. With a mediator mass well below the electroweak scale, these effects are potentially observable in a variety of contexts, including coherent elastic neutrino-nucleus scattering (CEvNS), neutrino deeply-inelastic scattering ($ν$DIS), and neutrino-electron scattering (e.g., at Borexino). Additionally, such effects lead to new contributions to the $Z$-boson decay width and to non-standard neutrino interactions relevant for long-baseline oscillation experiments. We explore all of these scenarios in some depth, building on the rich phenomenology associated with neutrinophilic mediators.

We investigate constraints on large extra dimensions (LED) using the latest results from reactor antineutrino experiments. Specifically, we analyze the full data sets from Daya Bay, RENO, KamLAND, NEOS, and STEREO to derive updated bounds. For the case of one extra dimension, we find constrains on its radius $a$ of $a \lesssim 0.58~{\rm μm}$ ($a \lesssim 0.12~{\rm μm}$) at the $99\%$ confidence level for normal (inverted) ordering, an improvement of approximately $\sim 20\%$ ($\sim 25\%$) with respect to previous bounds, assuming a massless lightest active neutrino. Furthermore, we present new limits on $4+d$ LED scenarios, with $d = 2, 3, 4$ denoting the number of extra dimensions, based on the same reactor data and assuming equal radii for all extra dimensions. We find that the constraints become increasingly stringent with a larger number of extra dimensions. In particular, $d = 4$ with a massless lightest active neutrino, we obtain limits of $a \lesssim 0.28~{\rm μm}$ for normal and $a \lesssim 0.05~{\rm μm}$ for inverted orderings at the $99\%$ confidence level.

We investigate the physics potential of SHIFT@LHC, a proposed gaseous fixed target installed in the LHC tunnel, as a novel source of detectable neutrinos. Using simulations of proton-gas collisions, hadron propagation, and neutrino interactions, we estimate that $O(10^4)$ muon-neutrino and $O(10^3)$ electron-neutrino interactions, spanning energies from 20 GeV to 1 TeV, would occur in the CMS and ATLAS detectors with 1% of the LHC Run-4 integrated luminosity. This unique configuration provides access to hadron production in the pseudorapidity range 5<$η$<8, complementary to existing LHC detectors. If realized, this would mark the first detection of neutrinos in a general-purpose LHC detector, opening a new avenue to study neutrino production and interactions in a regime directly relevant to atmospheric neutrino experiments.

Upcoming precision long-baseline neutrino oscillation experiments will be severely limited by the large systematic uncertainties associated with neutrino flux predictions and neutrino--nucleus cross sections. A promising remedy is the PRISM (Precision Reaction Independent Spectrum Measurement) technique, whereby the near detector measures the neutrino spectrum at different angles with respect to the beam axis. These measurements are then linearly combined into a prediction of the oscillated neutrino flux at the far detector. This prediction is data-driven, but still dependent on some theoretical knowledge about the neutrino flux. In this paper, we study to what extent off-axis measurements themselves can be used to directly constrain neutrino flux models. In particular, we use them to extract separately the fluxes and spectra of different meson species in the beam. We call this measurement LENS (Lateral Extraction of Neutrino Spectra). Second, we demonstrate how the thus improved flux model helps to further constrain the far detector flux prediction, thereby ultimately improving oscillation measurements.

In this work, we emphasize that it is necessary to take into account one-loop corrections of $2.0\%$ to the neutrino matter potential in the precision measurements of neutrino oscillation parameters and in the experimental searches for new physics beyond the Standard Model. With the numerical simulation of the DUNE experiment, we study how radiative corrections to the matter potential affect neutrino oscillation probabilities, and thus, the event rates in the presence of neutrino non-standard interactions (NSIs). We find that neglecting one-loop corrections may lead to wrong conclusions for the discovery of NSIs. The implications for the determination of neutrino mass ordering and constraints on the NSI parameters in future long-baseline accelerator neutrino experiments are explored in a quantitative way.

The diffuse supernova neutrino background (DSNB) created by stellar core-collapses throughout cosmic history is on the verge of discovery, with SK-Gd showing early deviations from the background expectation and JUNO starting to take data. However, the interpretation of early DSNB data will face significant challenges due to degeneracies between astrophysical parameters and uncertainties in supernova neutrino modeling. We explore how complementary astronomical observations can break these degeneracies and, in this context, we investigate whether early DSNB observations can constrain invisible supernovae, which have no optical emission but are powerful neutrino sources before being swallowed by a forming black hole. Leveraging the differences in the spectra between invisible and visible supernovae, we estimate the sensitivity of 1) detecting the existence of invisible supernovae, and 2) determining the fraction of invisible supernovae. Finally, we discuss how these conclusions depend on the spectral parameters of the black hole-forming component.

With the forthcoming deployment of IceCube-Upgrade, unprecedented statistics of atmospheric neutrinos in the energy range (1-100) GeV will become available, providing a valuable opportunity to probe physics beyond the Standard Model in the neutrino sector. In this study, we calculate the sensitivity of the IceCube-Upgrade to sterile neutrinos with mass-squared splittings $\lesssim 1~{\rm eV}^2$. We demonstrate that, particularly due to the (1-10) GeV energy window, $ν_μ-ν_s$ mixing angles as small as $\sim5^\circ$ can be probed by IceCube-Upgrade for all mass-squared splittings below $1~{\rm eV}^2$. Furthermore, we investigate the potential impact of a sterile neutrino state on the precision determination of standard atmospheric neutrino mixing parameters in the IceCube-Upgrade.

Perturbations in the cosmic neutrino background produce a characteristic phase shift in the acoustic oscillations imprinted in the anisotropies of the cosmic microwave background (CMB), providing a unique observational probe of neutrino physics. In this work, we explore how this phase shift signature is altered in the presence of neutrino interactions with temperature-dependent scattering rates, motivated by physical constructions for neutrino self-interactions and neutrino-dark matter couplings. A key finding is that the phase shift in these realistic models -- characterized by gradual rather than instantaneous decoupling -- maintains the same functional form as the free-streaming template, with only the asymptotic amplitude decreasing for stronger interactions that delay decoupling. This simple parametrization enables us to directly constrain neutrino interactions through phase shift measurements in the temperature and polarization power spectra from CMB observations. Analyzing the latest data from \textit{Planck}, the Atacama Cosmology Telescope, and the South Pole Telescope, we derive strong constraints on the neutrino decoupling redshift. Our global analysis indicates that neutrinos have been freely streaming since deep within the radiation-dominated epoch. We also explore flavor-dependent scenarios in which only one neutrino species interacts. Overall, our work establishes a signature-driven framework that exploits the clean phase shift signal in the acoustic oscillations of the CMB as a precise and robust probe of non-standard neutrino interactions in the early universe.

The IceCube Neutrino Observatory has detected a flux of $\sim 1-10 \, {\rm TeV}$ neutrinos from the active galaxy, NGC 1068. The soft spectral index of these neutrinos has previously been interpreted as an indication that this source accelerates protons only up to energies of several hundred TeV. Here, we propose that this source might instead accelerate protons to significantly higher energies, but that the charged pions and muons produced in their interactions undergo significant synchrotron energy losses before they can decay, leading to a cutoff in the neutrino spectrum at TeV-scale energies. This scenario would require very strong magnetic fields to be present in the acceleration region of NGC 1068, on the order of $B \sim 10^7 \, {\rm G}$. We point out that this synchrotron cooling would impact the flavor ratios of the neutrinos from this source, providing a means to test this scenario with future very-large volume neutrino telescopes.

The fermionic nature of neutrinos and the origin of their tiny masses remain unresolved issues in particle physics, intrinsically connected to lepton number symmetry-conserved for Dirac, violated for Majorana, and effectively pseudo-Dirac when global symmetries invoked for conservation are broken by quantum gravity. We investigate whether distinctive gravitational-wave (GW) signatures can illuminate the nature of neutrino masses and their underlying symmetries, particularly in scenarios where Yukawa couplings are not unnaturally small. To this end, we consider the minimal $B-L$ gauge extension of the Standard Model, where quantum numbers of beyond-SM states determine the neutrino nature and the scale of spontaneous $B-L$ breaking governs mass generation. In this framework, we show that neutrinos yield characteristic GW spectra: Majorana neutrinos with high-scale breaking ($\sim 10^{14}$ GeV) produce local cosmic strings and a flat spectrum across broad frequencies, Dirac neutrinos with low-scale breaking ($\sim 10^{7}$ GeV) generate peaked spectra from first-order phase transitions, and pseudo-Dirac scenarios give kink-like features from domain wall annihilation.

We introduce the first oscillation-independent astrophysical method to probe non-standard neutrino interactions (NSI) in core-collapse supernovae. Using a self-consistent treatment of NSI effects in both supernova neutrino emission simulations and flavor independent neutral-current scattering in detectors, we show that anti-correlated coincidence signatures between liquid scintillator experiments such as JUNO and dark matter detectors such as DARWIN/XLZD, ARGO, or RES-NOVA break degeneracy between NSI and flavor conversions effects. For a Galactic supernova within $\lesssim1$ kpc this approach enables independent probes of neutrino-quark NSI couplings in parameter space overlapping and extending beyond existing terrestrial limits. Our results establish a novel oscillation-independent avenue to test fundamental neutrino interactions in extreme astrophysical environments.

We present a comprehensive sensitivity study of future CE$ν$NS detectors, focusing on a cryogenic cesium iodide detector and a tonne-scale liquid argon one, currently being developed by the COHERENT Collaboration. These setups will enable precision measurements of the weak mixing angle at low energies and allow accurate extraction of the neutron nuclear distribution radius. We also demonstrate that next-generation detectors will place constraints on the neutrino charge radius comparable to or better than current global fits. In addition, we explore the sensitivity to non standard neutrino electromagnetic properties, such as magnetic moments and millicharges, as well as new mediators. These findings reinforce the role of CE$ν$NS experiments in the upcoming precision era, with future detectors playing a key role in advancing our understanding of neutrino interactions and electroweak physics at low energies.

We show that the neutral current data of the MINOS and MINOS+ experiments can provide information on the axial neutral current non-standard interactions of neutrinos with the $u$ and $d$ quarks; {\it i.e.,} on $ε_{αβ}^{Aq}$. We derive bounds on the $ee$, $eτ$ and $ττ$ components of these couplings and show that the MINOS(+) bounds on $ε^{Aq}_{eτ}$ and $ε^{Aq}_{ττ}$ are currently the world leading ones. The bound on the isospin singlet case, $ε^{Au}_{ττ}=ε^{Ad}_{ττ}$ is of particular interest because while this isospin singlet NSI is theoretically motivated, it was practically unconstrained before these results.

We develop a simulation within GENIE of the excitation of baryonic resonances by boosted dark matter. This work completes the simulation of all scattering modes for dark matter entering a detector at relativistic speeds. At some boosts, resonant scattering can contribute over 30% to the scattering rate. This channel offers a potentially powerful probe of the isospin structure of dark matter interactions via the relative prominence of the isospin-changing $Δ$ resonance. We study the estimated sensitivity of large volume detectors such as DUNE, Hyper-Kamiokande, and JUNO to all dark matter scattering modes and demonstrate the expected improvement in sensitivity when resonant scattering is included.

We propose an unprecedented detection of reactor $\overlineν^{}_e \to \overlineν^{}_μ$ and $\overlineν^{}_e \to \overlineν^{}_τ$ oscillations by using elastic antineutrino-electron scattering processes $\overlineν^{}_α+ e^- \to \overlineν^{}_α+ e^-$ (for $α= e, μ, τ$), among which the $\overlineν^{}_e$ events can be singled out by accurately measuring the $\overlineν^{}_e$ flux via the inverse beta decay $\overlineν^{}_e + p \to e^+ + n$. A proof-of-concept study shows that such measurements will not only be able to test the conservation of probability for reactor antineutrino oscillations, but also offer a new possibility to probe leptonic CP violation at the one-loop level.

We propose heavy decaying dark matter (DM) as a new probe of the cosmic neutrino background (C$ν$B). Heavy DM, with mass $\gtrsim 10^9$ GeV, decaying into neutrinos can be a new source of ultrahigh-energy (UHE) neutrinos. Including this contribution along with the measured astrophysical and predicted cosmogenic neutrino fluxes, we study the scattering of UHE neutrinos with the C$ν$B via standard weak interactions mediated by the $Z$ boson. We solve the complete neutrino transport equation, taking into account both absorption and reinjection effects, to calculate the expected spectrum of UHE neutrino flux at future neutrino telescopes, such as the IceCube-Gen2 radio. We argue that such observations can be used to probe the C$ν$B properties and, in particular, local C$ν$B clustering. We find that, depending on the absolute neutrino mass and the DM mass and lifetime, a local C$ν$B overdensity $\gtrsim 10^6$ can be probed at the IceCube-Gen2 radio within ten years of data taking.

An analytic and numerical systematic study of the neutrino mass matrix with one texture zero is presented in a basis where the charged leptons are diagonal. Under the assumption that neutrinos are Dirac particles, the analysis is carried out in detail for the normal and inverted hierarchy mass spectrum. Our study is performed without any approximations, first analytically and then numerically, using current neutrino oscillation data. The analysis constrains the parameter space in such a way that, among the six possible one-texture-zero patterns, only four are favored in the normal hierarchy and, one in the inverted hierarchy, by current oscillation data at the $3 σ$ level. Phenomenological implications for the lepton CP-violating phase and neutrino masses are also explored.

Given the $3\times 3$ Cabibbo-Kobayashi-Maskawa (CKM) quark flavor mixing matrix $V$, we define a new set of rephasing invariants in terms of the "trios" of its nine elements: $\lozenge^{ijk}_{αβγ} \equiv (V^{}_{αi} V^{}_{βj} V^{}_{γk})/\det V$ with $α\neq β\neq γ$ and $i \neq j \neq k$ running respectively over $(u, c, t)$ and $(d, s, b)$. We find that ${\rm Im} \lozenge^{ijk}_{αβγ} = - {\cal J}$ holds, where ${\cal J}$ is the well-known Jarlskog invariant of weak CP violation. Analogous rephasing invariants $\blacklozenge^{ijk}_{αβγ} \equiv (U^{}_{αI} U^{}_{βj} U^{}_{γk})/\det U$ can be defined for the $3\times 3$ Pontecorvo-Maki-Nakagawa-Sakata (PMNS) lepton flavor mixing matrix $U$, where $α\neq β\neq γ$ and $i \neq j \neq k$ run respectively over $(e, μ, τ)$ and $(1, 2, 3)$. Taking into account small non-unitarity of $U$ based on the canonical seesaw mechanism for neutrino mass generation, we calculate ${\rm Im} \blacklozenge^{ijk}_{αβγ}$ with the help of a full Euler-like block parametrization of the seesaw flavor structure and demonstrate that their leading terms converge to a universal invariant ${\cal J}^{}_ν$ in the unitarity limit of $U$.

The recent detection of the solar neutrino background at Dark Matter direct detection experiments paves the way to fully explore an important degeneracy in neutrino oscillations in the presence of new interactions, named the LMA-Dark degeneracy. This degeneracy makes it impossible to determine the neutrino mass ordering in oscillation experiments if neutrinos have new vectorial interactions with matter. As the composition of solar neutrinos at the Earth consists of all three neutrino flavors, testing the presence of new neutrino interactions in the muon and tau neutrino sector in scatterings can fully probe the LMA-Dark region for the first time. In this paper we show that current data from XENONnT and PandaX-4T does not yet exclude the LMA-Dark region with equal couplings of a new mediator to muon and tau neutrinos and quarks, and we identify the possible experimental scenarios to do so in the future. We also show that Dark Matter experiments can distinguish new interactions in the muon or tau sector only from new interactions affecting both sectors.

The recent detection of the solar neutrino background at Dark Matter direct detection experiments paves the way to fully explore an important degeneracy in neutrino oscillations in the presence of new interactions, named the LMA-Dark degeneracy. This degeneracy makes it impossible to determine the neutrino mass ordering in oscillation experiments if neutrinos have new vectorial interactions with matter. As the composition of solar neutrinos at the Earth consists of all three neutrino flavors, testing the presence of new neutrino interactions in the muon and tau neutrino sector in scatterings can fully probe the LMA-Dark region for the first time. In this paper we show that current data from XENONnT and PandaX-4T does not yet exclude the LMA-Dark region with equal couplings of a new mediator to muon and tau neutrinos and quarks, and we identify the possible experimental scenarios to do so in the future. We also show that Dark Matter experiments can distinguish new interactions in the muon or tau sector only from new interactions affecting both sectors.

We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we show that the capture of collisionless dark matter by a growing SMBH also substantially contributes, in some cases by an order of magnitude to the final SMBH mass. In particular, we show that a small seed stellar-remnant black hole can more easily reach $> 10^7$ M$_{\odot}$ by $z = 10$ in the core of dense nuclear star clusters when dark matter is included. This remains true for either cold dark matter or ultralight dark matter if the mass of the ULDM particle is $^>_\sim 10^{-20}$ eV. We highlight the unique evolution of ULDM capture by the growing SMBH when the ULDM de Broglie wavelength exceeds the initial nuclear star cluster half-mass radius.

CPT-odd effects on the neutrino charge radius are studied within the Standard Model Extension. We consider CPT violation from the electroweak Yang-Mills sector, characterized by Lorentz-violating coefficients $(k_1)_μ$ and $(k_2)_μ$, which have positive mass units. The $\barννγ$ vertex arises at tree level via exchange of two $Z$ bosons. Although suppressed by $\frac{1}{m_Z^4}$, this process is notable. The vertex function $Γ_μ$ includes three independent gauge structures satisfying the Ward identity $q^μΓ_μ= 0$, characteristic of neutral particles, and induces gauge-independent electromagnetic form factors. Besides charge and anapole, two novel form factors appear. The charge form factor $f_Q(q^2)$ contains an energy-dependent term causing $f_Q(0)\neq 0$, so electromagnetic properties are undefined for real photons with CPT violation. Instead, $f_Q$ and the charge radius are defined in the static limit: $q^0=0$ and $\mathbf{q}\to 0$. Here, $f_Q(0, \mathbf{0})=0$ and a correction to the SM neutrino charge radius is found: \[ \langle r^2_ν\rangle_{CPTV} = \frac{3c_{2W}}{2c_W^4} \left[\frac{k_2^2}{m_Z^2} + \frac{\mathbf{k}_2^2}{m_Z^2}\cos^2θ_γ\right] \frac{1}{m_Z^2}, \] with $θ_γ$ the angle between $\mathbf{q}$ and $\mathbf{k}_2$. Using recent bounds on $(k_i)_μ$ and reasonable assumptions, we obtain a small correction $\langle r^2_ν\rangle_{CPTV} \leq 0.83 \times 10^{-51}\ \mathrm{cm}^2$.

Muon accelerators, a potential technology for enabling $\mathcal{O}$(10 TeV) parton center of mass energy collisions, would also source an intense, collimated beam of neutrinos at TeV energies. The energy and size of this beam would be excellently matched as a source for existing and planned neutrino telescopes: gigaton-sized detectors of astrophysical neutrinos at and above TeV energies. In this paper, we introduce the technical considerations and scientific reach of pairing a muon accelerator source of neutrinos with a neutrino telescope detector, a combination we dub the ''Neutrino Kaleidoscope''. In particular, such a pairing would enable searches for non-standard oscillations of the beam neutrinos as they traverse the earth between source and detector. These non-standard neutrino oscillations could be sourced by Lorentz invariance violation, which a neutrino kaleidoscope could probe up to the quantum gravity-motivated Planck scale. Such a search would also have a reach on sterile neutrinos orders of magnitude beyond existing terrestrial limits. Finally, we touch on some of the non-oscillation potential of a neutrino kaleidoscope.

Time reversal (T) symmetry violations in neutrino oscillations imply the presence of an $L$-odd component in the transition probability at fixed neutrino energy, with $L$ denoting the distance between neutrino source and detector. Within the standard three-flavour framework, we show that the combination of the transition probabilities determined at the DUNE and T2HK experiments can establish the presence of an $L$-odd component, and therefore provide sensitivity to T violation, up to $4σ$ significance. The optimal neutrino energy window is from 0.68 to 0.92 GeV, and therefore a crucial role is played by the low-energy part of the DUNE event spectrum covering the second oscillation maximum. We compare the sensitivity to T violation based on this energy range using neutrino data only with the more traditional search for charge-parity (CP) violation based on the comparison of neutrino versus anti-neutrino beam data. We show that for DUNE it is advantageous to run in neutrino mode only, i.e., searching for T violating effects, whereas T2HK is more sensitive to CP violation, comparing neutrino and anti-neutrino data. Hence, the two experiments offer complementary methods to determine the complex phase in the PMNS mixing matrix.

We present a global neutrino oscillation analysis of models with a single large extra dimension in which right-handed neutrinos possess bulk Dirac masses. Two scenarios are considered: Large Extra Dimensions with bulk masses and the Dark Dimension framework, both predicting a tower of sterile Kaluza-Klein states that mix with active neutrinos. Using data from MINOS/MINOS+, KamLAND, and Daya Bay, we perform a joint likelihood analysis. No signatures of these theories were found. Therefore, we constrain the compactification radius under different bulk mass and Yukawa coupling assumptions. Large positive bulk masses or sizable Yukawas lead to strong bounds, while small couplings or negative bulk masses remain less constrained.

A flux of ultra-high-energy (UHE) neutrinos, produced by astrophysical sources at cosmological distances, is anticipated to exist and reach Earth. In this paper, we investigate the impact on the total flux, energy spectrum, and arrival directions of UHE neutrinos of neutrino-dark matter (DM) scatterings. We study scatterings both in the intergalactic medium and in the Milky Way. We emphasize the complementarity among neutrino detectors at different latitudes, that can probe anisotropies induced by neutrinos scattering with the Milky Way DM halo. We also discuss that, with mild astrophysical assumptions, limits on the DM-$ν$ scattering cross section can be placed even if the neutrino sources are unknown. Finally, we explore all this phenomenology with the recent UHE neutrino event KM3230213A, and place the corresponding limits on the DM-$ν$ scattering cross section.

Supernova cooling provides a powerful probe of physics beyond the Standard Model (SM), in particular for new, light states interacting feebly with SM particles. In this work, we investigate for the first time the production of fermionic dark matter (DM) via the neutrino-devouring process inside a core-collapse supernova, which contributes to the excessive cooling. By incorporating state-of-the-art supernova simulation data and the full time evolution information, we derive stringent and robust limits on DM interactions. We exclude the cross sections down to $10^{-51}-10^{-58}$ cm$^2$ in the keV-MeV mass range for DM-electron scattering, and $10^{-49}-10^{-56}$ cm$^2$ in the 0.1-100 MeV mass range for DM-nucleon scattering, supplemented by complementary constraints from cosmology, astrophysics, LHC and direct detection experiments in the larger cross section regime. We also close almost the entire window in which fermionic DM constitutes $\mathcal{O}(1)$ fraction of DM for its coupling to electrons in the keV-MeV mass range.

Neutrinos, being massive, can decay. A heavier neutrino could decay into a lighter one and a massless scalar or pseudoscalar boson, such as the Majoron. Two-body non-radiative decay could occur in dense matter, such as in the inner dense regions of a core-collapse supernova. We first derive novel bounds on neutrino-Majoron couplings using the spectral distortions induced by neutrino non-radiative two-body decay in matter, and two-dimensional likelihood analyses of the 24 $\barν_e$ events from SN1987A. We then explore the prospects of neutrino-Majoron couplings from a future galactic core-collapse supernova, leaving either a neutron star or a black-hole. To this aim, we use information from detailed one-dimensional supernova simulations. We consider the supernova neutrino signal associated with inverse-beta decay in the upcoming JUNO and Hyper-Kamiokande detectors, with neutrino-argon scattering in DUNE, or with coherent neutrino-nucleus scattering in the DARWIN experiment. In a full 3$ν$ framework, based on the spectral distortions induced by neutrino decay in matter, we perform two-dimensional likelihood analyses and provide prospects for the limits on neutrino-Majoron couplings. Our results show that the observation of a future supernova will significantly improve on the current bounds, in particular from SN1987A and neutrinoless double-beta decay. Finally, we explore the impact of neutrino decay in matter on the diffuse supernova neutrino background formed by past supernova explosions. We show for the first time that the effects on black-hole contributions are important and modify the DSNB number of events by several tens of percent in Hyper-Kamiokande.

The gallium anomaly, a persistent discrepancy exceeding $4σ$ in the $^{71}$Ga neutrino capture rates from $^{51}$Cr and $^{37}$Ar radioactive sources by the GALLEX, SAGE, and recently BEST experiments, has challenged particle physics and nuclear theory for over three decades. We present a new calculation of the neutrino capture cross section, abandoning the conventional leading-order approximation for electronic wave functions by numerically solving the Dirac-Coulomb equation for both bound and continuum electron states. Finally, we reevaluate the gallium anomaly, updating its global significance and presenting the most up-to-date status of its interpretation in terms of sterile neutrinos.

Neutrino non-standard interactions (NSI) play a crucial role in neutrino oscillations and can provide valuable insights for constructing models of neutrino masses and mixing. While NSI have been widely explored through oscillation and scattering experiments, as well as in cosmological and astrophysical contexts, we focus on probing them at future lepton colliders like the ILC, CLIC, and FCC-$ee$. If NSI arise from heavy mediators above the electroweak scale, these colliders can offer superior sensitivity compared to neutrino experiments across a broad mass range. A notable outcome is that lepton collider data can help resolve parameter degeneracies seen in oscillation studies. We find that large NSI scenarios, proposed to address the tension between T2K and NO$ν$A results, can be completely tested at such collider facilities. We also explore the potential of future colliders like the FCC to probe leptonic NSI using lepton PDFs in proton-proton collisions.

The gallium anomaly has a global significance of greater than $5σ$. Most viable BSM solutions quickly run into strong tensions with reactor and solar neutrino data. We propose to use indium (${}^{115}\text{In}$) as a target as it offers a low threshold and reasonably high cross section. The neutrino-indium charged current cross section can be calibrated using the well-constrained solar ${}^{7}\text{Be}$ neutrino flux that lies very close in energy to the ${}^{51}\text{Cr}$ neutrino lines. The triple coincidence provided by ${}^{115}\text{In}$ neutrino capture can be fully exploited by an opaque scintillation detector that also provides energy and position information. We show that a $100$ ton indium target combined with 2 source runs of a $3.4$ MCi ${}^{51}\text{Cr}$ source can probe the complete parameter space of the gallium anomaly, both in the context of a vanilla sterile neutrino as well as more involved BSM scenarios.

Recently, there has been interest in the applicability of quantum statistics to distinguish Dirac from Majorana neutrinos in multi-neutrino final states. In particular, debate has arisen over the validity of the Dirac-Majorana confusion theorem in these processes, i.e. that any distinction between the Dirac and Majorana processes goes to zero as the neutrino mass goes to zero. Here we approach this problem equipped with spinor-helicity methods generalized for massive Dirac and Majorana fermions. We explicitly calculate all helicity amplitudes for the decay of a light scalar particle to two neutrinos and two oppositely charged leptons. This allows us to pinpoint the crucial steps which could lead to claims of a violation of the confusion theorem. We show that if the correct anti-symmetrization of Dirac to Majorana amplitudes is used, identification of which is clear in this framework, and all relevant contributions are appropriately summed, a scalar decay into two charged leptons and two neutrinos satisfies the Dirac-Majorana confusion theorem.

In this work, we explore the influence of off-diagonal non-standard interaction (NSI) parameters on quantum entanglement within the three-flavor neutrino oscillation framework. By expressing three key entanglement measures: Entanglement of Formation (EOF), Concurrence, and Negativity in terms of oscillation probabilities, we analyze how these quantum correlations are affected by the NSI parameters $ε_{eμ}$, $ε_{eτ}$, and $ε_{μτ}$, including their complex phases. The quantum correlation measures considered in this work cannot be extracted directly from event rates, but solely in terms of oscillation probabilities. Using the DUNE experiment as a reference point, our analysis shows that NSI effects are most pronounced at lower energies, while Negativity continuing to dominate even at higher energies. It is observed that $ε_{e μ}$ and $ε_{e τ}$ affect entanglement measures mainly through the appearance channel, while the impact of $ε_{μτ}$ on EOF, Concurrence, and Negativity is predominantly linked to the disappearance channel. Further, our results show that Negativity is more sensitive than EOF and Concurrence in the [Energy ($E$) - $δ_{CP}$] plane under the influence of off-diagonal NSI scenarios, displaying a clear dependence of the CP-violating phase, $δ_{CP}$ on specific energy ranges, particularly in the lower energy regime.

We present a formula for the Dirac CP phase $δ= \arg ( U_{e1} U_{e2} U_{μ3} U_{τ3} / U_{e3} \det U_{\rm MNS} )$, directly derived from the lepton mixing matrix in an arbitrary basis of phases. In contrast to the numerically suppressed Jarlskog invariant, this expression is computationally simple and less sensitive to approximations. We apply the formula to derive general perturbative corrections from charged-lepton mixing $s_{ij}^{e}$ to the underlying CP phase of neutrinos $δ_ν$. A compact analytic expressions $δ= δ_ν + s_{12}^{e} D_{12} + s_{13}^{e} D_{13} + s_{23}^{e} D_{23}$ shows that these corrections can substantially exceed $O(10^{\circ})$, potentially within the reach of future long-baseline experiments such as DUNE and T2HK.

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

A sensitivity study of the search for heavy sterile neutrinos ($ν_H$) in the MeV mass range using solar neutrino experiments is presented. $ν_H$, with masses ranging from a few MeV up to around 15 MeV, can be produced in the Sun through $^8$B decay and subsequently decay into $ν_e e^+ e^-$. Its flux and lifetime strongly depend on the mixing parameter $|U_{eH}|^2$ and mass $m_{ν_H}$. The $ν_H$ signal can be detected via its decay products, either the $e^+e^-$ pair or $ν_e$, depending on whether $ν_H$ decays inside or outside the detector. Expected signal yields for both detection methods (detecting $e^+e^-$ or $ν_e$ signal) are presented across the full $|U_{eH}|^2$ and $m_{ν_H}$ parameter space. These two methods are found to be complementary in different regions of the $|U_{eH}|^2$ and $m_{ν_H}$ phase space. By combining both approaches, we anticipate observing at least a handful of signal events across most of the parameter space of $10^{-6} < |U_{eH}|^2 < 1$ and 2 MeV $< m_{ν_H} < $ 14 MeV, assuming a 500-ton solar neutrino experiment operating for one year. Key variables, such as the energy spectra and opening angle of $ν_e$ or $e^+e^-$ and the solar angle of $ν_e$ and its scattered electron, are also discussed to help distinguish signal from major backgrounds, such as solar neutrino events.

A critical challenge in particle physics is combining results from diverse experimental setups that measure the same physical quantity to enhance precision and statistical power, a process known as a global fit. Global fits of sterile neutrino searches, hunts for additional neutrino oscillation frequencies and amplitudes, present an intriguing case study. In such a scenario, the key assumptions underlying Wilks' theorem, a cornerstone of most classic frequentist analyses, do not hold. The method of Feldman and Cousins, a trials-based approach which does not assume Wilks' theorem, becomes computationally prohibitive for complex or intractable likelihoods. To bypass this limitation, we borrow a technique from simulation-based inference (SBI) to estimate likelihood ratios for use in building trials-based confidence intervals, speeding up test statistic evaluations by a factor $>10^4$ per grid point, resulting in a faster, but approximate, frequentist fitting framework. Applied to a subset of sterile neutrino search data involving the disappearance of muon-flavor (anti)neutrinos, our method leverages machine learning to compute frequentist confidence intervals while significantly reducing computational expense. In addition, the SBI-based approach holds additional value by recognizing underlying systematic uncertainties that the Wilks approach does not. Thus, our method allows for more robust machine learning-based analyses critical to performing accurate but computationally feasible global fits. This allows, for the first time, a global fit to sterile neutrino data without assuming Wilks' theorem. While we demonstrate the utility of such a technique studying sterile neutrino searches, it is applicable to both single-experiment and global fits of all kinds.

This paper presents a method for uncovering hidden analytic relationships among the fundamental parameters of the Standard Model (SM), a foundational theory in physics that describes the fundamental particles and their interactions, using symbolic regression and genetic programming. Using this approach, we identify the simplest analytic relationships connecting pairs of these constants and report several notable expressions obtained with relative precision better than 1%. These results may serve as valuable inputs for model builders and artificial intelligence methods aimed at uncovering hidden patterns among the SM constants, or potentially used as building blocks for a deeper underlying law that connects all parameters of the SM through a small set of fundamental constants.

We explore the sensitivity of the Deep Underground Neutrino Experiment (DUNE) to sterile neutrino oscillations within a $3+$(pseudo-Dirac pair) framework. We first consider a pair of two sterile neutrinos forming a pseudo-Dirac pair, then we consider a low-scale seesaw realization, that we name ``Linear-Inverse Seesaw" model. This scenario features two nearly degenerate sterile neutrino states at the keV scale, characterized by a small mass splitting arising from a small amount of lepton number violation. In this scenario, the oscillation behavior can be described in three distinct regimes depending on the sterile-sterile mass-squared difference : low ($< 1\,\mathrm{eV}^2$), resonant ($1$--$100\,\mathrm{eV}^2$), and high ($> 100\,\mathrm{eV}^2$) regimes, recovering in both low- and high-mass regimes an effective non-unitarity of the leptonic mixing matrix. A distinctive feature of this framework is that observable effects persist even in the low-mass limit, unlike the case of standard $3+1$ scenarios, due to rapid oscillation averaging from larger keV-scale splittings. We leverage the complementarity of both near and far detectors to explore the sensitivity for $ν_e$ and $ν_μ$ disappearance and $ν_e$ and $ν_τ$ appearance oscillation probabilities. Our analysis reveals that DUNE can achieve significant improvements over current experimental constraints, especially in neutrino appearance modes. Additionally, we show that new CP-violating phases associated with the sterile sector can dramatically alter the sensitivity, with destructive interference potentially suppressing signals by orders of magnitude.

Supernova-neutrino-boosted dark matter (SN$ν$ BDM) has emerged as a promising portal for probing sub-GeV dark matter. In this work, we investigate the behavior of BDM signatures originating from core-collapse supernovae within the Milky Way (MW) over the past one hundred thousand years, examining both their temporal evolution and present-day spatial distributions. We show that while the MW BDM signature is approximately diffuse in the nonrelativistic regime, it exhibits significant temporal variation and spatial localization when the BDM is relativistic. Importantly, we compare these local MW signatures with the previously proposed diffuse SN$ν$ BDM (DBDM), which arises from the accumulated flux of all past supernovae in the Universe [Y.-H. Lin and M.-R. Wu, Phys. Rev. Lett. 133, 111004 (2024)]. In the nonrelativistic limit, DBDM consistently dominates over the local diffuse MW BDM signature. Only when the MW BDM becomes ultrarelativistic and transitions into a transient, highly-localized signal can it potentially surpass the DBDM background. This work thus reinforces the importance of DBDM for SN$ν$ BDM searches until the next galactic SN offers new opportunities.

Nontrivial electromagnetic properties of neutrinos are an avenue to physics beyond the Standard Model. To this end, we investigate the power of monophoton signals at neutrino experiments to probe a higher-dimensional operator connecting neutrinos to SM photons dubbed, neutrino polarizability. A simplified scenario giving rise to this operator involves a new pseudo-scalar that couples to both neutrinos and photons, with clear implications for axion-like particle (ALP) and Majoron physics. By analyzing the photon energy spectrum and angular distributions, we find that NOMAD and MiniBooNE currently set the most stringent limits, while SBND and the DUNE near detector will soon provide significantly improved constraints.

The Deep Underground Neutrino Experiment (DUNE) primarily aims to measure the yet unknown parameters of the standard three neutrino framework, i.e., the determination of Dirac CP phase ($δ_{13}$), neutrino mass hierarchy (MH) and octant of $θ_{23}$. In the present work, we consider the standard three neutrino paradigm (referred to as the $(3+0)$ case) and beyond with an additional light sterile neutrino (referred to as the $(3+1)$ case). We consider two configurations : standard energy resolution as in DUNE Technical Design Report (TDR) and improved energy resolution and study the impact of energy resolution in the $(3+0)$ and $(3+1)$ cases. In general, inclusion of subdominant new physics effects spoils the sensitivities. However, improved energy resolution leads to enhancement in sensitivities to the three unknowns in both $(3+0)$ and $(3+1)$ cases.

Micro-pattern gaseous detectors (MPGDs) are a class of technologies that enable the full three-dimensional spatial reconstruction of ionisation tracks from nuclear and electron recoils in gas. Anticipating near-future 30 m$^3$-scale time projection chambers with MPGD-based readout, we forecast the sensitivity of such directionally-sensitive low-energy recoil detectors to neutrino interactions beyond the Standard Model. We work in the framework of neutrino non-standard interactions (NSIs), and calculate the combined recoil energy-angle distributions of the electron recoil signal generated by solar neutrinos in atmospheric-pressure He:CF$_4$ gas. We estimate the expected exclusion limits that such an experiment could place on various NSI parameters, as well as the mass and coupling of a new light mediator that interacts with electrons and neutrinos. We find that with an achievable background reduction of around a factor of ten from current estimates for a 30 m$^3$ optical-readout detector using this gas mixture, sensitivity to NSI parameters would already approach Borexino's sensitivity. Directionality also allows for event-by-event neutrino energy reconstruction, which would provide a means to resolve some parameter degeneracies present in the modified neutrino cross section in this formalism. Our results strongly motivate the development of small-scale directionally-sensitive gas detectors for neutrino physics.

Particle physics theories, such as those which explain neutrino flavor mixing, arise from a vast landscape of model-building possibilities. A model's construction typically relies on the intuition of theorists. It also requires considerable effort to identify appropriate symmetry groups, assign field representations, and extract predictions for comparison with experimental data. We develop an Autonomous Model Builder (AMBer), a framework in which a reinforcement learning agent interacts with a streamlined physics software pipeline to search these spaces efficiently. AMBer selects symmetry groups, particle content, and group representation assignments to construct viable models while minimizing the number of free parameters introduced. We validate our approach in well-studied regions of theory space and extend the exploration to a novel, previously unexamined symmetry group. While demonstrated in the context of neutrino flavor theories, this approach of reinforcement learning with physics software feedback may be extended to other theoretical model-building problems in the future.

We study the sensitivity to the decay of a heavy neutral lepton into $e^+e^-$-pairs using the solar boron-8 neutrino flux as source. We provide a fully differential cross section for this process including the interference of neutral and charged current amplitudes. We revisit a previous bound from Borexino and make predicitions for the expected sensitivity in future large liquid noble gas detectors, like XLZD, Argo and DUNE, as well as high-resolution scintillator detectors based on the LiquidO technology. We find that more than two orders of magnitude improvement in mixing angle reach is possible relative to existing bounds.

The Cosmological Principle, which states that the Universe is homogeneous and isotropic (when averaged on large scales), is the foundational assumption of Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies such as the current standard Lambda-Cold-Dark-Matter (ΛCDM) model. This simplification yields an exact solution to the Einstein field equations that relates space and time through a single time-dependent scale factor, which defines cosmological observables such as the Hubble parameter and the cosmological redshift. The validity of the Cosmological Principle, which underpins modern cosmology, can now be rigorously tested with the advent of large, nearly all-sky catalogs of radio galaxies and quasars. Surprisingly, the dipole anisotropy in the large-scale distribution of matter is found to be inconsistent with the expectation from kinematic aberration and Doppler boosting effects in a perturbed FLRW universe, which is the standard interpretation of the observed dipole in the cosmic microwave background (CMB). Although the matter dipole agrees in direction with that of the CMB dipole, it is anomalously larger, demonstrating that either the rest frames in which matter and radiation appear isotropic are not the same, or that there is an unexpected intrinsic anisotropy in at least one of them. This discrepancy now exceeds 5σ in significance. We review these recent findings, as well as the potential biases, systematic issues, and alternate interpretations that have been suggested to help alleviate the tension. We conclude that the cosmic dipole anomaly poses a serious challenge to FLRW cosmology, and the standard ΛCDM model in particular, as an adequate description of our Universe.

The quantum gravity scale within the dark dimension scenario ($M_* \sim 10^{9}~{\rm GeV}$) roughly coincides with the energy scale of the KM3-230213A neutrino ($E_ν\sim 10^{8}~{\rm GeV}$). We propose an interpretation for this intriguing coincidence in terms of Hawking evaporation of five-dimensional (5D) primordial black holes (PBHs). 5D PBHs are bigger, colder, and longer-lived than 4D PBHs of the same mass. For brane observers, PBHs residing in the higher-dimensional bulk decay essentially invisibly (only through gravitationally and sterile coupled modes). As a consequence, constraints on the density of PBHs relative to that of dark matter from null searches of Hawking evaporation can be avoided. We demonstrate that Hawking evaporation of 5D bulk PBHs can explain the KM3-230213A neutrino, evade constraints from upper limits on the gamma-ray flux, and remain consistent with IceCube upper limits on the partial decay width of superheavy dark matter particles into neutrinos.

The recent KM3NeT observation of an ${\cal{O}}(100~{\rm PeV})$ event KM3-230213A is puzzling because IceCube with much larger effective area times exposure has not found any such events. We propose a novel solution to this conundrum in terms of dark matter (DM) scattering in the Earth's crust. We show that intermediate dark-sector particles that decay into muons are copiously produced when high-energy ($\sim100~\text{PeV}$) DM propagates through a sufficient amount of Earth overburden. The same interactions responsible for DM scattering in Earth also source the boosted DM flux from a high-luminosity blazar. We address the non-observation of similar events at IceCube via two examples of weakly coupled long-lived dark sector scenarios that satisfy all existing constraints. We calculate the corresponding dark sector cross sections, lifetimes and blazar luminosities required to yield one event at KM3NeT, and also predict the number of IceCube events for these parameters that can be tested very soon. Our proposed DM explanation of the event can also be distinguished from a neutrino-induced event in future high-energy neutrino flavor analyses, large-scale DM direct detection experiments, as well as at future colliders.

We entertain the possibility that transient astrophysical sources can produce a flux of dark particles that induce ultra-high-energy signatures at neutrino telescopes such as IceCube and KM3NeT. We construct scenarios where such ``dark flux" can produce meta-stable dark particles inside the Earth that subsequently decay to muons, inducing through-going tracks in large-volume neutrino detectors. We consider such a scenario in light of the $\mathcal{O}(70)$~PeV ultra-high-energy muon observed by KM3NeT and argue that because of its location in the sky and the strong geometrical dependence of the signal, such events would not necessarily have been observed by IceCube. Our model relies on the upscattering of a new particle $X$ onto new metastable particles that decay to dimuons with decay lengths of $\mathcal{O}(100)$~km. This scenario can explain the observation by KM3NeT without being in conflict with the IceCube data.

It has been claimed in a number of publications that neutrinos can exhibit chirality oscillations. In this note we discuss the notion of chirality and show that chiral neutrino oscillations in vacuum do not occur. We argue that the incorrect claims to the contrary resulted from a failure to clearly discriminate between quantum fields, states and wave functions. We also emphasize the role played in the erroneous claims on the possibility of chirality oscillations by the widely spread misconceptions about negative energies.

We investigate the capabilities of upcoming kiloton-scale neutrino detectors, such as Hyper-Kamiokande, in determining the primary cosmic ray spectrum. These detectors provide full-sky coverage and long-term monitoring, unlike traditional satellite and balloon experiments that measure cosmic ray flux at specific altitudes and locations. By analyzing the atmospheric neutrino flux generated by cosmic ray interactions, we demonstrate that future detectors can differentiate between various cosmic ray models with high statistical significance, even when accounting for uncertainties in neutrino cross sections and hadronic interactions. We introduce a technique for reconstructing the primary cosmic ray spectrum using neutrino measurements, which reduces the flux uncertainty from approximately 20\% to about 7\%. We then show that Hyper-K has the potential to increase sensitivity to neutrino oscillation parameters, such as $\sin^2θ_{23}$, by a factor of 2. Our results highlight the complementary role of neutrino detectors in cosmic ray physics and their critical importance for precision measurements in particle astrophysics.

The search for neutrino magnetic moments offers a valuable window into physics beyond the Standard Model. However, a common misconception arises in the interpretation of experimental results: the assumption that the so-called effective neutrino magnetic moment is a universal, experiment-independent quantity. In reality, this effective parameter depends on the specific characteristics of each experiment, including the neutrino source, flavor composition or energy spectrum. As a result, the effective magnetic moment derived from solar neutrino data differs fundamentally from that obtained in reactor or accelerator-based experiments. Treating these quantities as directly comparable can lead to misleading conclusions. In this work, we clarify the proper definition of the effective neutrino magnetic moment in various experimental contexts and discuss the implications of this misconception for global analyses and theoretical interpretations.

In the canonical seesaw mechanism, the strengths of charged-current interactions for light and heavy Majorana neutrinos are described respectively by the $3\times 3$ matrices $U$ and $R$ that are correlated with each other via the exact seesaw relation and the unitarity condition. We write out the Majorana-type invariants of CP violation of $R$ and $U$, which are insensitive to redefining the phases of three charged-lepton fields; and the Dirac-type invariants of CP violation of $R$ and $U$ that are insensitive to the rephasing of both the charged-lepton fields and the neutrino fields. Such invariants are explicitly calculated with the help of a full Euler-like block parametrization of the seesaw flavor structure containing nine active-sterile flavor mixing angles and six independent CP-violating phases, and their corresponding roles in the CP-violating asymmetries of three heavy Majorana neutrino decays and in the flavor oscillations of three light Majorana neutrinos are briefly discussed. We point out that similar rephasing invariants arising from the interplay between $R$ and $U$ may also manifest themselves in a variety of lepton-flavor-violating and lepton-number-violating processes.

We investigate how neutrinos may acquire small electric charges within the Standard Model framework while preserving electromagnetic gauge invariance. Instead of gauging the standard hypercharge generator $Y$, a linear combination of $Y$ and a new generator $X$ from a gaugable global $U(1)_X$ symmetry is embedded, under which neutrinos transform non-trivially. We demonstrate that minimal scenarios based on flavor-dependent $U(1)_X$ symmetries, such as $X = L_α- L_β$, are incompatible with current neutrino oscillation data. In contrast, we have shown that only flavor-universal $U(1)_X$ symmetries-such as $U(1)_{B-L}$, which shifts both quark and lepton charges, and $U(1)_L$, which modifies only the lepton sector-can generate tiny neutrino charges consistent with observed masses and mixing. We also discuss the necessary connection between such charges and the Dirac nature of neutrinos. By analyzing the phenomenological implications in detail, our findings emphasize that constraints on neutrino charges should be evaluated within the specific framework of the $U(1)_X$ symmetry under consideration, rather than assuming a generic approach, as is often the case.

In this work, we investigate in a quantitative way how much radiative corrections to the matter potential for neutrino oscillations can impact the sensitivity to neutrino mass ordering in long-baseline accelerator experiments. Using numerical simulations for the future experiment DUNE, we find that the statistical significance for excluding the incorrect mass ordering can be enhanced by about $0.4σ$ if a one-loop correction of $2.0\%$ -- based on the Fermi coupling constant $G^{}_μ$ derived from measurements of muon lifetime -- is included. The radiative corrections at one-loop level lead to resolving the neutrino mass ordering at $5σ$ confidence level 4-9 days earlier than at tree level. In contrast, the sensitivity to leptonic CP violation in DUNE is essentially unchanged. Finally, we emphasize that one-loop corrections should be incorporated into analyses of future neutrino oscillation data in a consistent and systematic manner.

Weak Gamow-Teller (GT) responses for low-lying states in ${}^{71}\mathrm{Ga}$ are crucial for studying low-energy solar neutrinos and the Ga anomaly, i.e., the possible transition to the sterile state. The responses for the ground state, the first excited state, and the second excited state are evaluated for the first time using the experimental electron capture rates, the experimental charge exchange reaction (CER) rates corrected for the tensor-interaction effect and the theoretical interacting shell model (ISM) calculations. The contributions from the two excited states to the solar and ${}^{51}\mathrm{Cr}$ neutrinos are found to be $4.2 \pm 1.2\%$ of that for the ground state. This is slightly larger than the ISM values but little smaller than the CER values without corrections for the tensor interaction effect. The Ga anomaly is far beyond the uncertainty of the obtained nuclear responses.

The Positron Annihilation into Dark Matter Experiment at the Laboratori Nazionali di Frascati has reported an excess of $e^+e^-$ final-state events from positron annihilation on fixed-target atomic electrons. While the global significance remains at the $(1.77\pm 0.15)\,σ$ level, the excess is centered around $\sqrt{s} \sim 17\,\text{MeV}$, coinciding with the invariant mass at which anomalous $e^+e^-$ pair production has previously been observed in nuclear transitions from excited to ground states in $^8$Be, $^4$He and $^{12}$C, thereby strengthening the case for a common underlying origin, possibly involving a hypothetical new $X_{17}$ boson. We discuss the significance of this independent accelerator-based evidence. Combining it with existing nuclear physics results, we obtain a value for the $X_{17}$ mass of $m_{X_{17}} = 16.88 \pm 0.05\,\text{MeV}$, reducing the uncertainty from nuclear physics determinations by more than a factor of two, and mitigating the impact of poorly known correlations among their systematic errors.

In the coming age of precision neutrino physics, neutrinos from the Sun become robust probes of the conditions of the solar core. Here, we focus on $^8$B neutrinos, for which there are already high precision measurements by the Sudbury Neutrino Observatory and Super-Kamiokande. Using only basic physical principles and straightforward statistical tools, we estimate projected constraints on the temperature and density of the $^8$B neutrino production zone compared to a reference solar model. We outline how to better understand the astrophysics of the solar interior using forthcoming neutrino data and solar models. Finally, we note that detailed forward modeling will be needed to develop the full potential of this approach.

The scattering of extremely energetic cosmic rays with both cosmic microwave background and extragalactic background light, can produce $\mathcal{O}(10^{18} \,{\rm eV})$ neutrinos, known as cosmogenic neutrinos. These neutrinos are the only messengers from the extreme cosmic accelerators that can reveal the origin of the most energetic cosmic rays. Consequently, much effort is being devoted to achieving their detection. In particular, the GRAND project aims to observe the $ν_τ$ and $\bar ν_τ$ components of the cosmogenic neutrino flux in the near future using radio antennas. In this work, we investigate how the detection of cosmogenic neutrinos by GRAND can be used to probe beyond the Standard Model physics. We identify three well-motivated scenarios which induce distinct features in the cosmogenic neutrino spectrum at Earth: neutrino self-interactions mediated by a light scalar ($ν$SI), pseudo-Dirac neutrinos (PD$ν$) and neutrinos scattering on ultra-light Dark Matter ($ν$DM). We show these scenarios can be tested by GRAND, using 10 years of cosmogenic neutrino data, in a region of parameter space complementary to current experiments. For the $ν$SI model,, we find that GRAND can constrain the coupling to $ν_τ$ in the range [$10^{-2},10^{-1}$] for a scalar with mass in the range 0.1 to 1 GeV. For PD$ν$, we find that GRAND is sensitive to sterile-active mass squared splitting in the range [$10^{-15},10^{-13}$] ${\rm eV}^2$. Finally, for the $ν$DM model, assuming a heavy mediator, GRAND can do substantially better than the current limits from other available data. These results rely on the fact that the actual cosmogenic flux is around the corner, not far from the current IceCube limit.

The correlations between successive measurements of a quantum system can violate a family of Leggett-Garg Inequalities (LGIs) that are analogous to the violation of Bell's inequalities of measurements performed on spatially separated quantum systems. These LGIs follow from a macrorealistic point of view, imposing that a classical system is at all times in a definite state and that a measurement can, at least in principle, leave this state undisturbed. Violations of LGIs can be probed by neutrino flavour oscillations if the correlators of consecutive flavour measurements are approximately stationary. We discuss here several improvements of the methodology used in previous analyses based on accelerator and reactor neutrino data. We argue that the strong claims of LGI violations made in previous studies are based on an unsuitable modelling of macrorealistic systems in statistical hypothesis tests. We illustrate our improved methodology via the example of the MINOS muon-neutrino survival data, where we find revised statistical evidence for violations of LGIs at the $(2-3)σ$ level, depending on macrorealistic background models.

The Standard Model (SM) of particle physics effectively explains most observed phenomena, though some anomalies, especially in the neutrino sector, suggest the need for extensions. In this Letter, we perform the first global fit of elastic neutrino-nucleus and neutrino-electron scattering data to further test the SM within a consistent framework. Our results on the neutrino charge radius, the only nonzero electromagnetic property of neutrinos in the SM, show no significant deviation, indicating no large beyond the SM flavor-dependent effects for electron and muon neutrinos. By incorporating solar neutrino data from dark matter direct detection experiments, we also place the most stringent constraints on the tau neutrino charge radius obtained from neutrino scattering experiments. Additionally, we determine updated constraints on the vector and axial-vector neutrino-electron neutral current couplings, adjusting for flavor-dependent effects and for the different experimental momentum transfers. The global analysis reveals two allowed solutions: one close to the SM prediction, and a degenerate solution that is favored. We show that future dark matter detectors could achieve sufficient precision to resolve the degeneracy. As we move toward the precision era, this Letter demonstrates the crucial need to properly account for flavor- and momentum-dependent effects to avoid misinterpretations of the data.

The weak mixing angle $θ_W$ is a fundamental parameter in the electroweak theory with a value running according to the energy scale, and its precision measurement in the low-energy regime is still ongoing. We propose a method to measure the low-energy $\sin{^2θ_W}$ by taking advantage of Argo, a future ton-scale liquid argon dark matter detector, and the neutrino flux from a nearby core-collapse supernova (CCSN). We evaluate the expected precision of this measurement through the coherent elastic neutrino-nucleus scattering (CE$ν$NS) channel. We show that Argo is potentially capable of achieving a few percent determination of $\sin{^2θ_W}$, at the momentum transfer of $q \sim 20$ MeV, in the observation of a CCSN within $\sim 3$ kpc from the Earth. Such a measurement is valuable for both the precision test of the electroweak theory and searching for new physics beyond the standard model in the neutrino sector.

Within the framework of general $U(1)$ scenario, we demonstrate that the ultra high energy neutrinos recently detected by KM3NeT could originate from a decaying right handed neutrino dark matter (DM), with a mass of 440 PeV. Considering DM production via freeze-in, we delineate the parameter space that satisfies the observed relic abundance and also lies within the reach of multiple gravitational wave detectors. Our study provides a testable new physics scenario, enabled by multi-messenger astronomy.

In this paper, we generally analyze the $μ- τ$ reflection symmetry modified by small mixings of charged leptons and how will future experiments verify deviations from the predictions of the symmetry. As an approximation, the left-handed diagonalization $U_{e}$ of charged leptons is assumed to have a similar magnitude as the CKM matrix. In other words, the 1-3 mixing is neglected and the 1-2 and 2-3 mixing are to be approximately $O(0.1)$. The Dirac CP phase $δ$ of the MNS matrix is evaluated in such parameter regions. As a result, deviations from the predictions $\sin θ_{23} = π/4$ and $δ= \pm π/2$ depend on relative CP phases between $U_{e}$ and diagonalization of neutrinos $U_ν$. While phases of the second and third generations cause only about $\pm 10^{\circ}$ deviations for the Dirac phase $δ$, the phase of the first generation can cause up to $\pm 30^{\circ}$. This flavor dependence is distinguished to some extent by the next-generation experiments. On the other hand, if $δ$ is not observed, such a scenario is excluded by about 5 years of observation.

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

We propose a novel cosmological scenario to explain the exceptional KM3-230213A neutrino event reported at an energy scale of $\mathcal{O}(100)$~PeV by the KM3NeT collaboration, along with its associated gravitational wave (GW) signatures. In our framework, ultra high energy neutrinos originate from the decay of a super-heavy sterile neutrino produced via the Hawking evaporation of primordial black holes (PBHs) in the early Universe. Employing an ultraviolet complete type-I seesaw model, we demonstrate that while two sterile neutrinos are responsible for light neutrino masses as required by oscillation data, one sterile neutrino can have an exceedingly feeble coupling, allowing its lifetime to be tuned so that its decay yields a neutrino flux consistent with the observed event. Furthermore, our scenario predicts two distinct GW signatures: one arising from gravitons emitted during PBH evaporation and another from the Bremsstrahlung process during the decay of the sterile neutrino. These complementary signals provide a multi-messenger probe of the underlying physics. Our results thus offer a compelling explanation for the KM3-230213A event and open new avenues for investigating the interplay between high-energy neutrino astronomy and gravitational wave cosmology.

In this work we investigate the impact of two phenomenological Beyond the Standard Model (BSM) scenarios concerning the role of neutrinos in the early universe: non-standard neutrino interactions (NSI) and non-unitary three-neutrino mixing. We evaluate the impact of these frameworks on two key cosmological observables: the effective number of relativistic neutrino species (\Neff), related to neutrino decoupling, and the abundances of light elements produced at Big Bang Nucleosynthesis (BBN). For the first time, neutrino CC-NSI with quarks and non-unitary three-neutrino mixing are studied in the context of BBN, and the constraints on such interactions are found to be remarkably restrictive. In particular, the BBN limits are competitive with the ones derived from terrestrial experiments for the non-diagonal CC-NSI parameter $\varepsilon^{udV}_{e α}$, with $α\neq e$ and for the non-unitarity parameter $α_{22}$. In the case of non-unitarity, the combination between neutrino decoupling and BBN imposes stringent constraints that can either mildly favour the existence of New Physics (NP), or reinforce the SM, depending on the choice of the experimental nuclear rates involved in the BBN calculation. These results stress the already noted need for further nuclear rates measurements in order to obtain more robust BBN theoretical predictions.

Quantum simulation of particle phenomena is a rapidly advancing field of research. With the widespread availability of quantum simulators, a given quantum system can be simulated in numerous ways, offering flexibility in implementation and exploration. Here, we perform quantum simulation of neutrino propagation in matter, a phenomenon that plays a crucial role in neutrino oscillations. We present quantum circuits with novel gate arrangements to simulate neutrino propagation in both constant and varying matter density profiles. The oscillation probabilities are determined by encoding and measuring the qubit states in the neutrino flavor basis, showing excellent agreement with theoretical predictions.

Although the sources of astrophysical neutrinos are still unknown, they are believed to be produced by a population of sources in the distant universe. Measurements of the diffuse, all-sky astrophysical flux can thus be sensitive to flavor and energy-dependent propagation effects, such as very long baseline oscillations. These oscillations are present in certain neutrino mass models, such as when neutrinos are quasi-Dirac. Assuming generic models for the source flux, we find that these oscillations can still be resolved even when integrated over wide distributions in source redshift. We use two sets of IceCube all-sky flux measurements, made with muon and all-flavor neutrino samples, to set constraints at the $3σ$ level on quasi-Dirac mass-splittings between $(5 \times 10^{-19}, 8 \times 10^{-19})~\textrm{eV}^2$. We also consider systematic uncertainties on the source population and find that our results are robust under alternate spectral hypotheses or physical redshift distributions. Our analysis shows that spectral features in the all-sky neutrino measurements provide strong constraints on massive neutrino scenarios and are sensitive to uncharted parameter space.

In this paper, we investigate the effects of $ν_τ$ and $\barν_τ$ detection at the DUNE far detector on the experiment's sensitivity to Non-Standard Interactions (NSI) in neutrino propagation. We show that the strongest observable NSI effect in the $ν_τ$ and $\barν_τ$ appearance probabilities arises from $ε_{μτ}$. We have studied the hierarchy sensitivity, CP violation sensitivity and octant sensitivity of DUNE from $ν_τ$ and $\barν_τ$ appearance channels in presence of NSI. We have also studied the detection sensitivity of NSI phases and the future constaints on NSI parameters from the tau neutrino appearance channels in DUNE. Additionally, we examine the role of $ν_τ$ detection in constraining the unitary nature of the PMNS matrix. These studies emphasize the importance of incorporating $ν_τ$ detection in long-baseline neutrino experiments such as DUNE.

We revisit the production of axion-like particles (ALPs) coupled to electrons at tree-level in a relativistic plasma. We explicitly demonstrate the equivalence between pseudoscalar and derivative couplings, incorporate previously neglected processes for the first time-namely, semi-Compton production ($γe^-\rightarrow a e^-$) and pair annihilation ($e^+e^-\rightarrow aγ$)-and derive analytical expressions for the bremsstrahlung ($e^- N\to e^- N a$) production rate, enabling a more computationally efficient evaluation of the ALP flux. Additionally, we assess uncertainties in the production rate arising from electron thermal mass corrections, electron-electron Coulomb interactions, and the Landau-Pomeranchuk-Migdal effect. The ALP emissivity is made available in a public repository as a function of the ALP mass, the temperature, and the electron chemical potential of the plasma. Finally, we examine the impact of ALP production and subsequent decays on astrophysical observables, deriving the leading bounds on ALPs coupling to electrons. At small couplings, the dominant constraints come from the previously neglected decay $a\to e^+ e^-γ$, except for a region of fireball formation where SN 1987A X-ray observations offer the best probe. At large couplings, bounds are dominated by the energy deposition argument, with a recently developed new prescription for the trapping regime.

Recently, the KM3NeT Collaboration announced the detection of a 220 PeV neutrino from the celestial coordinates RA=94.3\degree~ and Dec=-7.8\degree~ on 13 February 2023 at 01:16:47 UTC \cite{KM3NeT:2025npi}. The source for this extra-ordinary cosmic neutrino, designated KM3-230213A, is not identified yet but there has been speculation that it might be associated with a gamma-ray burst GRB~090401B \cite{Amelino-Camelia:2025lqn}. The purpose of this report is to search the association of this 220 PeV neutrino with potential GRB sources from a more general consideration of Lorentz invariance violation (LV) without predefined LV scale. We try to associate this extra-ordinary neutrino with potential GRBs within angular separation of 1\degree, 3\degree~ and 5\degree~ respectively and the results are listed in Table 1. We find the constraints $E_{\rm{LV}}\leq 5.3\times 10^{18}$~GeV for subluminal LV violation and $E_{\rm{LV}}\leq 5.6\times 10^{19}$~GeV for superluminal LV violation if KM3-230213A is a GRB neutrino.

Current data on ultra-high-energy (UHE) cosmic rays suggest they are predominantly made of heavy nuclei. This indicates that the flux of neutrinos produced from proton collisions on the cosmic microwave background is small and hard to observe. Motivated by the recent extremely-high-energy muon event reported by KM3NeT, we explore the possibility of enhancing the energy-flux of cosmogenic neutrinos through nuclear photodisintegration in the presence of new physics. Specifically, we speculate that UHE neutrons may oscillate into a new state, dark (or mirror) neutron $n'$ that in turn decays injecting large amount of energy to neutrinos, $n\to n'\to ν_\text{UHE}$. While this mechanism does not explain the tension between the KM3NeT event and null results from IceCube, it reconciles the experimental preference for a heavier cosmic ray composition with a large diffuse cosmogenic flux of UHE neutrinos.

The sterile neutrino interpretation of the LSND and MiniBooNE neutrino anomalies is currently being tested at three Liquid Argon detectors: MicroBooNE, SBND, and ICARUS. It has been argued that a degeneracy between $ν_μ\to ν_e$ and $ν_e \to ν_e$ oscillations significantly degrades their sensitivity to sterile neutrinos. Through an independent study, we show two methods to eliminate this concern. First, we resolve this degeneracy by including external constraints on $ν_e$ disappearance from the PROSPECT reactor experiment. Second, by properly analyzing the full three-dimensional parameter space, we demonstrate that the stronger-than-sensitivity exclusion from MicroBooNE alone already covers the entire 2$σ$ preferred regions of MiniBooNE at the level of $2-3σ$. We show that upcoming searches at SBND and ICARUS can improve on this beyond the $4σ$ level, thereby providing a rigorous test of short-baseline anomalies.

We study the complementarity between COHERENT and LHC searches in testing neutrino nonstandard interactions (NSIs) through the completion of the effective field theory approach within a $Z'$ simplified model. Our results show that LHC bounds are strongly dependent on the $Z'$ mass, with relatively large masses excluding regions in the parameter space that are allowed by COHERENT data and its future expectations. We demonstrate that the combination of low- and high-energy experiments results in a viable approach to break NSI degeneracies within the context of simplified models.

We update constraints on a simple model of self-interacting neutrinos involving a heavy scalar mediator with universal flavor coupling. According to past literature, such a model is allowed by Cosmic Microwave Background (CMB) data, with some CMB and large-scale structure data even favoring a strongly-interacting neutrino (SI$ν$) scenario over $Λ$CDM. In this work, we re-evaluate the constraints on this model in light of the new Planck NPIPE data, DESI BAO data, and the Effective Field Theory of Large Scale Structures (EFTofLSS) applied to BOSS data. We find that Planck NPIPE are more permissive to the SI$ν$ scenario and that DESI data favor the SI$ν$ over $Λ$CDM. However, when considering EFTofBOSS data, this mode is no longer preferred. Therefore, new DESI data analyzed under the EFTofLSS are particularly awaited to shed light on this disagreement.

Many geophysical and geochemical phenomena in the Earth's interior are related to physical and chemical processes in the outer core and the core-mantle boundary, which are directly linked to the isotopic composition. Determining the composition using standard geophysical methods has been challenging. Atmospheric neutrino oscillations, influenced by their weak interactions with terrestrial matter, offer a new way to gather valuable information about the Earth's internal structure and, in particular, to constrain the composition of the core. If neutrinos had as yet unknown non-standard interactions (NSI), this could affect their propagation in matter and consequently impact studies of Earth's composition using neutrino oscillation tomography. This study focuses on scalar-mediated NSI and their potential impact on atmospheric neutrino oscillations, which could obscure information about the hydrogen content in the outer core. In turn, compositional uncertainties could affect the characterization of NSI parameters. The analysis is based on a Monte-Carlo simulation of the energy distribution and azimuthal angles of neutrino-generated $μ$ events. Using a model of the Earth consisting of 55 concentric shells with constant densities determined from the PREM, we evaluate the effect on the number of events due to changes in the outer core composition (Z/A)$_{oc}$ and the NSI strength parameter $ε$. To examine the detection capability to observe such variations, we consider regions in the plane of (Z/A)$_{oc}$ and $ε$ where the statistical significance of the discrepancies between the modified Earth model and the reference model is less than $1σ$.

Supernova cooling has long been used to constrain physics beyond the Standard Model, typically involving new mediators or dark matter (DM) particles that couple to nucleons or electrons. In this work, we show that the large density of neutrinos inside the neutrinosphere of supernovae also makes them powerful laboratories to study nonstandard neutrino interactions with a {\it neutrinophilic} dark sector, i.e.~DM and mediator particles interacting primarily with neutrinos. In this case, we find that the existing constraints are rather weak, and for a wide range of currently unconstrained parameter space, neutrino annihilation within a supernova could copiously produce such neutrinophilic DM at a large enough rate to cause noticeable anomalous cooling. From the non-observation of such anomalous cooling in SN1987A, we thus set new constraints on neutrino-DM interactions, which provide up to four orders of magnitude improvement over the existing constraints for DM masses below ${\cal O}$(100 MeV).

Investigating the correlation between the TDE population and IceCube neutrinos could help us better understand whether TDEs could be potential high-energy neutrino emitters. In this paper, we perform a systematic search for TDEs that are associated with neutrinos in a sample including 143 IceCube neutrino alert events and 52 TDEs classified by the Zwicky Transient Facility (ZTF) - Bright Transient Survey (BTS). Furthermore, considering that the TDEs/TDE candidates reported as potential IceCube neutrino emitters are all accompanied by infrared (IR) echo emissions, we further select the TDEs with IR echoes from these 52 TDEs as a subsample to examine the correlation with neutrinos. Based on the Wide-field Infrared Survey Explorer (WISE) mission database, seven TDEs are identified as having IR echoes. Then we employ Monte Carlo simulations to quantify the correlation between the TDE sample/subsample and IceCube neutrinos. Finally, after considering spatial and temporal criteria, the seven TDEs with IR echoes show the most significant correlation at a 2.46$σ$ confidence level. If we tentatively further take the time delay factor into account, the correlation enhances to a 2.66$σ$ confidence level. The correlation is primarily contributed by two TDEs: AT2019dsg and AT2019azh. The latter's association with a neutrino alert, IC230217A, is newly reported in this work. We discussed the possible physical connection between AT2019azh and the neutrino event IC230217A.

The origin of neutrino masses remains unknown to date. One popular idea involves interactions between neutrinos and ultralight dark matter, described as fields or particles with masses $m_φ\ll 10\,\mathrm{eV}$. Due to the large phase-space number density, this type of dark matter exists in coherent states and can be effectively described by an oscillating classical field. As a result, neutrino mass-squared differences undergo field-induced interference in spacetime, potentially generating detectable effects in oscillation experiments. We demonstrate that if $m_φ\gg 10^{-14}\,\mathrm{eV}$, the mechanism becomes sensitive to dark matter density fluctuations, which suppresses the oscillatory behavior of flavor-changing probabilities as a function of neutrino propagation distance in a model-independent way, thereby ruling out this regime. Furthermore, by analyzing data from the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), a benchmark long-baseline reactor experiment, we show that the hypothesis of a dark origin for the neutrino masses is disfavored for $m_φ\ll 10^{-14}\,\mathrm{eV}$, compared to the case of constant mass values in vacuum. This result holds at more than the 4$σ$ level across different datasets and parameter choices. The mass range $10^{-17}\,\mathrm{eV} \lesssim m_φ\lesssim 10^{-14}\,\mathrm{eV}$ can be further tested in current and future oscillation experiments by searching for time variations (rather than periodicity) in oscillation parameters.

In the present work we have investigated some patterns of broken ``scaling" ansatz of the neutrino mass matrix. The scaling neutrino mass matrix is disallowed by the current neutrino oscillation data as, among others, it predicts vanishing reactor angle ($θ_{13}=0$). We study its possible breaking scenarios in light of the large mixing angle (LMA) and Dark-LMA solutions suggested by current neutrino oscillation data. The normal hierarchical neutrino mass spectrum is ruled out in all three possible breaking patterns. Also, one of the interesting features of these breaking scenarios is the interplay between $θ_{23}$-octant and possible CP violation. We find that the model allows maximal CP violation for $θ_{23}$ above $6\%$ of its maximal value which, interestingly, is close to its current best-fit value for inverted hierarchical neutrino masses. We have, also, investigated the implications for effective Majorana neutrino mass parameter $|M_{ee}|$ for allowed breaking patterns. The correlation behavior of Majorana CP phases, which can be probed in $0νββ$ decay experiments, is found to have the capability of distinguishing LMA and Dark-LMA solutions.

We perform an updated global analysis of the known and unknown parameters of the standard $3ν$ framework as of 2025. The known oscillation parameters include three mixing angles $(θ_{12},\,θ_{23},\,θ_{13})$ and two squared mass gaps, chosen as $δm^2=m^2_2-m^2_1>0$ and $Δm^2=m^2_3-{\textstyle\frac{1}{2}}(m^2_1+m^2_2)$, where $α=\mathrm{sign}(Δm^2)$ distinguishes normal ordering (NO, $α=+1$) from inverted ordering (IO, $α=-1$). With respect to our previous 2021 update, the combination of oscillation data leads to appreciably reduced uncertainties for $θ_{23}$, $θ_{13}$ and $|Δm^2|$. In particular, $|Δm^2|$ is the first $3ν$ parameter to enter the domain of subpercent precision (0.8\% at $1σ$). We underline some issues about systematics, that might affect this error estimate. Concerning oscillation unknowns, we find a relatively weak preference for NO versus IO (at $2.2σ$), for CP violation versus conservation in NO (1.3$σ$) and for the first $θ_{23}$ octant versus the second in NO ($1.1σ$). We discuss the status and qualitative prospects of the mass ordering hint in the plane $(δm^2,\,Δm^2_{ee})$, where $Δm^2_{ee}=|Δm^2|+{\textstyle\frac{1}{2}}α(\cos^2θ_{12}-\sin^2θ_{12})δm^2$, to be measured by the JUNO experiment with subpercent precision. We also discuss upper bounds on nonoscillation observables. We report $m_β<0.50$~eV and $m_{ββ}<0.086$~eV ($2σ$). Concerning the sum of neutrino masses $Σ$, we discuss representative combinations of data, with or without augmenting the $Λ$CDM model with extra parameters accounting for possible systematics or new physics. The resulting $2σ$ upper limits are roughly spread around the bound $Σ< 0.2$~eV within a factor of three. [Abridged]

We obtain stringent bounds on neutrino quantum decoherence from the analysis of SN1987A data. We show that for the decoherence model considered here, which allows for neutrino-loss along the trajectory, the bounds are many orders of magnitude stronger than the ones that can be obtained from the analysis of data from reactor neutrino oscillation experiments or neutrino telescopes.

The recent observation of the ultrahigh-energy neutrino event KM3-230213A by the KM3NeT experiment offers a compelling avenue to explore physics beyond the Standard Model (SM). In this paper, we explore a simplest possibility that this event originates from the decay of a super-heavy dark matter (SHDM). We consider a minimal scenario where the SHDM decays to neutrino and SM Higgs. We derive constraints on the DM lifetime as a function of DM mass, ensuring consistency with IceCube, Auger upper limits, and the observed KM3-230213A event, along with the gamma-ray constraints. We find that KM3-230213A gives stringent constraint on the DM mass ranging from $1.5\times10^8$ GeV to $5.2\times10^9$ GeV with lifetime in the range: $1.42\times10^{30}$ s to $5.4\times10^{29}$ s. Remarkably, in our SHDM scenario, the apparent tension between the KM3NeT observation and the nonobservation of this event by IceCube and Auger can be reduced to below $1.2σ$. Our results are applicable to any neutrinophilic SHDM models while evading gamma-ray constraints.

We assess the effect of the Cosmic Neutrino Background (C$ν$B) on superradiant instabilities caused by an ultralight scalar field around spinning black holes (BHs). When the scalar couples to neutrinos via a Yukawa interaction, thermal corrections from the C$ν$B induce a quartic self-interaction and an effective mass term for the scalar. We show that, for Yukawa couplings as small as $y_{φν} \sim 10^{-16}$ (for astrophysical BHs) or $10^{-20}$ (for supermassive BHs), the quartic term can quench the instability and set observable bounds, even if the scalar does not constitute dark matter. We assess the robustness of these constraints against several sources of uncertainty, including gravitational focusing of relic neutrinos, galactic clustering, and non-linear backreaction. An enhanced local neutrino density weakens the bounds by up to an order of magnitude compared to a uniform background, yet the induced self-interaction remains strong enough to significantly affect the superradiant dynamics. Our results open a new observational window on neutrino-coupled scalars via BH superradiance.

We study the possibility of the highest energy neutrino event with 220 PeV energy, detected recently by the KM3NeT experiment to be originating from heavy dark matter (DM) decay. Considering a heavy right handed neutrino (RHN) DM for illustrative purpose, we show that DM mass of 440 PeV, can explain the observed flux. The required DM lifetime to produce the best-fit value of the neutrino flux saturates the existing gamma-ray bounds. Due to the large uncertainty in the flux, it is possible to explain the KM3NeT event from RHN DM decay at $3σ$ confidence level (CL) while being in agreement with gamma-ray bounds and non-observation of similar events at IceCube. While we consider a gauged $B-L$ scenario where DM relic can be generated due to other interactions, we also briefly discuss some alternate DM possibilities where the gamma-ray bounds can be alleviated compared to the minimal RHN DM discussed here.

The KM3NeT collaboration recently reported the observation of KM3-230213A, a neutrino event with an energy exceeding 100 PeV, more than an order of magnitude higher than the most energetic neutrino in IceCube's catalog. Given its longer data-taking period and larger effective area relative to KM3NeT, IceCube should have observed events around that energy. This tension has recently been quantified to lie between $2σ$ and $3.5σ$, depending on the neutrino source. A $\mathscr{O}(100)$ PeV neutrino detected at KM3NeT has traversed approximately $147$ km of rock and sea en route to the detector, whereas neutrinos arriving from the same location in the sky would have only traveled through about $14$ km of ice before reaching IceCube. We use this difference in propagation distance to address the tension between KM3NeT and IceCube. Specifically, we consider a scenario in which the source emits sterile neutrinos that partially convert to active neutrinos through oscillations. We scrutinize two such realizations, one where a new physics matter potential induces a resonance in sterile-to-active transitions and another one where off-diagonal neutrino non-standard interactions are employed. In both cases, sterile-to-active neutrino oscillations become relevant at length scales of $\sim100$ km, resulting in increased active neutrino flux near the KM3NeT detector, alleviating the tension between KM3NeT and IceCube. Overall, we propose the exciting possibility that neutrino telescopes may have started detecting new physics.

Deviations from unitarity of the CKM matrix in the quark sector are considered excellent windows to probe physics beyond the Standard Model. In its leptonic counterpart, the PMNS matrix, these searches are particularly motivated, as the new physics needed to generate neutrino masses often leads to non-unitary mixing among the standard neutrinos. It is then interesting to consider how neutrino oscillations are affected in such scenario. This simple question is, however, subject to several subtleties: What is the correct way to define oscillation probabilities for a non-unitary mixing matrix? Do these probabilities add up to one? Does a non-unitary mixing matrix lead to observable flavor transitions at zero distance? What is the interplay between unitarity constraints obtained from neutrino oscillations and from electroweak precision data? This work aims to shed light on these issues and to clarify the corresponding misconceptions commonly found in the literature. We also compile updated bounds from neutrino oscillation searches to compare with those from flavour and electroweak precision observables.

We investigate whether the ultra high energy neutrino inferred by the recent KM3NeT observation could have originated from an evaporating black hole. Given the characteristics of black hole (BH) evaporation mechanism, any object capable of producing particles in the energy range of the detected event (around 100-800 PeV) must have a mass below 10^7 g. No known astrophysical mechanism can generate black holes of such low mass, leaving primordial black holes (PBHs)-potentially formed at the end of cosmic inflation-as the only viable candidates. Black holes with masses below 10^7 g have lifetimes shorter than 10^-5 seconds, meaning PBHs in this mass range should have fully evaporated by now. However, recent studies suggest that quantum effects, collectively referred to as the "memory burden", may slow down black hole evaporation, potentially extending the lifetimes of low-mass PBHs to timescales comparable to or exceeding the Hubble time. We systematically explore the parameter space of memory-burdened PBHs, assuming that they constitute a fraction of the dark matter (f-PBH) within current constraints, and identify viable regions that could explain the KM3-230213A event. We further predict the occurrence rate of similar events and find that KM3NeT's current configuration could test this scenario within a few years.

The IceCube Neutrino Observatory is an optical Cherenkov detector instrumenting one cubic kilometer of ice at the South Pole. The Cherenkov photons emitted following a neutrino interaction are detected by digital optical modules deployed along vertical strings within the ice. The densely instrumented bottom central region of the IceCube detector, known as DeepCore, is optimized to detect GeV-scale atmospheric neutrinos. As upward-going atmospheric neutrinos pass through Earth, matter effects alter their oscillation probabilities due to coherent forward scattering with ambient electrons. These matter effects depend upon the energy of neutrinos and the density distribution of electrons they encounter during their propagation. Using simulated data at the IceCube Deepcore equivalent to its 9.3 years of observation, we demonstrate that atmospheric neutrinos can be used to probe the broad features of the Preliminary Reference Earth Model. In this contribution, we present the preliminary sensitivities for establishing the Earth matter effects, validating the non-homogeneous distribution of Earth's electron density, and measuring the mass of Earth. Further, we also show the DeepCore sensitivity to perform the correlated density measurement of different layers incorporating constraints on Earth's mass and moment of inertia.

The discovery of solar neutrinos confirmed that the inner workings of the Sun generally match our theoretical understanding of the fusion process. Solar neutrinos have also played a role in discovering that neutrinos have mass and that they oscillate. We combine the latest solar neutrino data along with other oscillation data from reactors to determine the Sun's density profile. We derive constraints given the current data and show the anticipated improvements with more reactor neutrino data from JUNO constraining the true oscillation parameters and more solar neutrino data from DUNE which should provide a crucial measurement of $hep$ neutrinos.

We present a framework for the analysis of data from neutrino oscillation experiments. The framework performs a profile likelihood fit and employs a forward-folding technique to optimize its model with respect to the oscillation parameters. It is capable of simultaneously handling multiple datasets from the same or different experiments and their correlations. The code of the framework is optimized for performance and allows for convergence times of a few seconds handling hundreds of fit parameters, thanks to multi-threading and usage of GPUs. The framework was developed in the context of the Double Chooz experiment, where it was successfully used to fit three- and four-flavor models to the data, as well as in the measurement of the energy spectrum of reactor neutrinos. We demonstrate its applicability to other experiments by applying it to a study of the oscillation analysis of a medium baseline reactor experiment similar to JUNO.

We report a study of the inelasticity distribution in the scattering of neutrinos of energy $80-560$ GeV off nucleons. Using atmospheric muon neutrinos detected in IceCube's sub-array DeepCore during 2012-2021, we fit the observed inelasticity in the data to a parameterized expectation and extract the values that describe it best. Finally, we compare the results to predictions from various combinations of perturbative QCD calculations and atmospheric neutrino flux models.

Recent results on the Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) on germanium present significant discrepancies among experiments. We perform a combined analysis of the Dresden-II, CONUS+ and COHERENT data, quantifying the impact of quenching factor uncertainties on their CE$ν$NS cross section measurement. No choice of quenching factor can bring these three data sets into mutual agreement, whereas the combination of COHERENT with either Dresden-II or CONUS+ agrees well albeit for very different quenching factors. We further study the quenching factor dependence on the sensitivity of these experiments to a large neutrino magnetic moment, finding that the constraints can vary by up to an order of magnitude. Our work highlights the importance of reducing this uncertainty on quenching factors in order to probe new physics from neutrinos at the low-energy frontier.

If there exist unstable but long-lived relics of the early universe, their decays could produce detectable fluxes of gamma rays and neutrinos. In this paper, we point out that the decays of superheavy particles, $m_χ \gtrsim 10^{10} \, \text{GeV}$,would produce an enhanced flux of ultra-high-energy neutrinos through the processes of muon and pion pair production in the resulting electromagnetic cascades. These processes transfer energy from electromagnetic decay products into neutrinos, relaxing the constraints that can be derived from gamma-ray observations, and increasing the sensitivity of high-energy neutrino telescopes to superheavy particle decays. Taking this into account, we derive new constraints on long-lived superheavy relics from the IceCube Neutrino Observatory, and from the Fermi Gamma-Ray Space Telescope. We find that IceCube-Gen2, and other next generation neutrino telescopes, will provide unprecedented sensitivity to the decays of superheavy dark matter particles and other long-lived relics.

We study the impact of unitarity violation on the sensitivity of the leptonic CP phase, $δ_{CP}$, considering the next generation of long-baseline neutrino experiments, Hyper-Kamiokande and DUNE. By simulating near and far detectors and assuming different scenarios for non-unitarity, we verify how it can affect the sensitivity to measure the $δ_{ CP}$ violating phase. We also probe the capability of these experiments to constrain the non-unitarity parameters and how their capability could be improved if the impact of non-unitarity at both near and the far detectors were properly taken into account. We find that the Hyper-Kamiokande experiment is robust in the presence of non-unitarity mixing, achieving a sensitivity above $5σ$ for our all considered cases. On the other hand, DUNE suffers somewhat more impact due to unitarity violation, reaching a sensitivity below 5$σ$ for some values of $δ_{CP}$. However, depending on the scenario adopted for non-unitarity, DUNE demonstrates robustness in the sensitivity to $δ_{ CP}$ phase.

Neutrino tensor interactions have gained prominence in the study of coherent elastic neutrino-nucleus scattering (CE$ν$NS) recently. We perform a systematical examination of the nuclear effect, which plays a crucial role in evaluating the cross section of CE$ν$NS in the presence of tensor interactions. Our analysis reveals that the CE$ν$NS cross section induced by tensor interactions is not entirely nuclear spin-suppressed and can be enhanced by a few orders of magnitude compared to the conventional studies. The neutrino magnetic moment induced by the loop effect of tensor interactions, is also taken into account due to its sizable contribution to the CE$ν$NS cross section. We also employ data from the COHERENT experiment and recent observations of solar $^8$B neutrinos from dark matter direct detection experiments to scrutinize the parameter space of neutrino tensor interactions.

In this paper, it is shown that $N$naturalness scenarios share the intrinsic mechanism to suppress neutrino masses with other infrared neutrino mass models. In such models like extra-dimensional theories or many species theories, the large number of mixing partners is responsible for the neutrino mass suppression. It is shown how neutrino mass matrices arise in $N$naturalness models and the resulting neutrino mixing is analyzed. The first result is that a totally democratic coupling among the different sectors like in the original models is already ruled out by the fact that neutrinos are not massless. In the case where the sector couplings deviate from the intersector ones a tower of additional neutrino mass eigenstates appears whose difference between the squared masses, $Δm_{ij}^2$, is determined fully by the theory. The resulting phenomenology of such a tower is investigated and the unique signals in neutrino oscillation experiments, neutrino mass measurements, and neutrinoless double beta decay experiments are discussed. This opens the door for terrestrial tests of $N$naturalness whose phenomenology was so far focused on Cosmology.

KM3NeT has reported the detection of a remarkably high-energy through-going muon. Lighting up about a third of the detector, this muon likely originated from a neutrino exceeding 10 PeV in energy. The crucial question we need to answer is where this event comes from and what its source is. Intriguingly, IceCube has been operating with a much larger effective area for a considerably longer time, yet it has not reported neutrinos above 10~PeV. We quantify the tension between the KM3NeT event and the absence of similar high-energy events in IceCube. Through a detailed analysis, we determine the most likely neutrino energy to be in the range of 23 - 2400 PeV. We find a $3.5σ$ tension between the two experiments, assuming the neutrino is from the diffuse isotropic neutrino flux. Alternatively, assuming the event is of cosmogenic origin and considering three representative models, this tension still falls within 3.1 - 3.6$σ$. The least disfavored scenario is a steady or transient point source, though still leading to $2.9σ$ and $2.0σ$ tensions, respectively. The lack of observation of high-energy events in IceCube seriously challenges the explanation of this event coming from any known diffuse fluxes. Our results indicate the KM3NeT event is likely the first observation of a new astrophysical source.

Oscillations of atmospheric muon and electron neutrinos produce tau neutrinos with energies in the GeV range, which can be observed by the ORCA detector of the KM3NeT neutrino telescope in the Mediterranean Sea. First measurements with ORCA6, an early subarray corresponding to about 5$\%$ of the final detector, are presented. A sample of 5828 neutrino candidates has been selected from the analysed exposure of 433 kton-years. The $ν_τ$ normalisation, defined as the ratio between the number of observed and expected tau neutrino events, is measured to be $S_τ= 0.48^{+0.5}_{-0.33}$. This translates into a $ν_τ$ charged-current cross section measurement of $σ_τ^{\text{meas}} = (2.5 ^{+2.6}_{-1.8}) \times 10^{-38}$ cm$^{2}$ nucleon$^{-1}$ at the median $ν_τ$ energy of 20.3 GeV. The result is consistent with the measurements of other experiments. In addition, the current limit on the non-unitarity parameter affecting the $τ$-row of the neutrino mixing matrix was improved, with $α_{33}>$ 0.95 at the 95$\%$ confidence level.

Coherent elastic neutrino-nucleus scattering (CE$ν$NS) is a key process for probing Standard Model and beyond the Standard Model (BSM) properties. Following its first detection by the COHERENT Collaboration, recent reactor-based experiments provide a unique opportunity to refine our current understanding. In particular, the high-precision data from CONUS+, combined with the strong bounds from TEXONO, not only validate the CE$ν$NS process at low energies but also provide improved constraints on the weak mixing angle, neutrino electromagnetic properties (including the charge radius, millicharge, and magnetic moment), and nonstandard interactions and light mediators. We also examine the role of elastic neutrino-electron scattering, which gains significance in certain BSM scenarios and allows us to obtain the best limit for the millicharge of the electron neutrinos. By combining reactor and higher-energy spallation neutron source measurements, this work strengthens CE$ν$NS as a precision tool for testing the Standard Model and beyond.

The CONUS+ collaboration has reported their first observation of coherent elastic neutrino-nucleus scattering (CE$ν$NS). The experiment uses reactor electron antineutrinos and germanium detectors with recoil thresholds as low as $160~\mathrm{eV_\text{ee}}$. With an exposure of $327$ kg $\times$ d, the measurement was made with a statistical significance of $3.7 σ$. We explore several physics implications of this observation, both within the standard model and in the context of new physics. We focus on a determination of the weak mixing angle, nonstandard and generalized neutrino interactions both with heavy and light mediators, neutrino magnetic moments, and the up-scattering of neutrinos into sterile fermions through the sterile dipole portal and new mediators. Our results highlight the role of reactor-based \cevns~experiments in probing a vast array of neutrino properties and new physics models.

Sterile neutrinos with masses on the $\mathrm{eV}$ scale are promising candidates to account for the origin of neutrino mass and the reactor neutrino anomalies. The mixing between sterile and active neutrinos in the early universe could result in a large abundance of relic sterile neutrinos, which depends on not only their physical mass $m_{\rm phy}$ but also their degree of thermalization, characterized by the extra effective number of relativistic degrees of freedom $ΔN_{\rm eff}$. Using neutrino-involved N-body simulations, we investigate the effects of sterile neutrinos on the matter power spectrum, halo pairwise velocity, and halo mass and velocity functions. We find that the presence of sterile neutrinos suppress the matter power spectrum and halo mass and velocity functions, but enhance the halo pairwise velocity. We also provide fitting formulae to quantify these effects.

Neutrino masses may have evolved dynamically throughout the history of the Universe, potentially leading to a mass spectrum distinct from the normal or inverted ordering observed today. While cosmological measurements constrain the total energy density of neutrinos, they are not directly sensitive to a dynamically changing mass ordering unless future surveys achieve exceptional precision in detecting the distinct imprints of each mass eigenstate on large-scale structures. In this work, we investigate the impact of a dynamic neutrino mass spectrum on the diffuse supernova neutrino background (DSNB), which is composed of neutrinos from all supernova explosions throughout cosmic history and is on the verge of experimental detection. Since neutrino oscillations are highly sensitive to the mass spectrum, we show that the electron neutrino survival probability carries distinct signatures of the evolving neutrino mass spectrum. Our results indicate that the resulting modifications to the DSNB spectrum would exhibit unique energy-dependent features. These features are distinguishable from the effects of significant astrophysical uncertainties, providing a potential avenue for probing the dynamic nature of neutrino masses.

The Sun can efficiently capture leptophilic dark matter that scatters with free electrons. If this dark matter subsequently annihilates into leptonic states, it can produce a detectable neutrino flux. Using 10 years of Super-Kamiokande observations, we set constraints on the dark-matter/electron scattering cross-section that exceed terrestrial direct detection searches by more than an order of magnitude for dark matter masses below 100 GeV, and reach cross-sections as low as $\sim$4$\times$10$^{-41}$cm$^{-2}$.

The Deep Underground Neutrino Experiment (DUNE) is a proposed long-baseline neutrino oscillation experiment that will project an on-axis wide-band neutrino beam over a distance of 1300 km to determine the unknowns in the neutrino sector. Given the baseline of 1300 km and the intense beam facility, DUNE is a promising experiment to study the sub-leading effects such as environmental decoherence, matter induced non-standard interactions (NSIs), neutrino decay, etc. In this study, we investigate how NSI and environmental decoherence affect the neutrino oscillation probabilities simultaneously. Considering the modified probabilities we obtain the updated mass hierarchy (MH) and CP violation (CPV) sensitivities of DUNE. Furthermore, we demonstrate the sensitivity of DUNE to distinguish between the effects of NSI and environmental decoherence.

Neutrinos and dark matter (DM) are two of the least understood components of the Universe, yet both play crucial roles in cosmic evolution. Clues about their fundamental properties may emerge from discrepancies in cosmological measurements across different epochs of cosmic history. Possible interactions between them could leave distinctive imprints on cosmological observables, offering a rare window into dark sector physics beyond the standard $Λ$CDM framework. We present compelling evidence that DM-neutrino interactions can resolve the persistent structure growth parameter discrepancy, $S_8 = σ_8\,\sqrt{Ω_m/0.3}$, between early and late universe observations. By incorporating cosmic shear measurements from current Weak Lensing surveys, we demonstrate that an interaction strength of $u \sim 10^{-4}$ not only provides a coherent explanation for the high-multipole observations from the Atacama Cosmology Telescope (\texttt{ACT}), but also alleviates the $S_8$ discrepancy. Combining early universe constraints with \texttt{DES Y3 cosmic shear} data yields a nearly $3σ$ preference for non-zero DM neutrino interactions. This strengthens previous observational claims and provides a clear path toward a significant breakthrough in cosmological research. Our findings challenge the standard $Λ$CDM paradigm and highlight the potential of future large-scale structure surveys, which can rigorously test this interaction and unveil the fundamental properties of DM.

A number of recent cosmological observations have indicated the presence of new physics beyond the $\mathbfΛ$CDM model. Combining observations from EMPRESS on helium abundance and DESI on baryon acoustic oscillations with Hubble tension, we show that all of them can be explained concurrently with a extension of the $\mathbfΛ$CDM model with primordial neutrino asymmetry $ξ_ν$ and additional contribution to the effective number of neutrinos $δN_{\rm eff}$. Based on the accurate treatments of neutrino decoupling and BBN processes, we present state-of-the-art constraints on neutrino asymmetry for the fixed or varying $N_{\rm eff}$. Comparing different extensions of the $\mathbfΛ$CDM model, we show that the neutrinophilic $\mathbfΛ$CDM extension with $ξ_ν = 0.056 \pm 0.017 $ and $δN_{\rm eff} = 0.41 \pm 0.16$ is preferred by current observations, while the Hubble tension in this model is also alleviated to be $2.2 σ$.

We explore the potential of the European Spallation Source (ESS) in probing physics within and beyond the Standard Model (SM), based on future measurements of coherent elastic neutrino-nucleus scattering (CE$ν$NS). We consider two SM physics cases, namely the weak mixing angle and the nuclear radius. Regarding physics beyond the SM, we focus on neutrino generalized interactions (NGIs) and on various aspects of sterile neutrino and sterile neutral lepton phenomenology. For this, we explore the violation of lepton unitarity, active-sterile oscillations as well as interesting upscattering channels such as the sterile dipole portal and the production of sterile neutral leptons via NGIs. The projected ESS sensitivities are estimated by performing a statistical analysis considering the various CE$ν$NS detectors and expected backgrounds. We find that the enhanced statistics achievable in view of the highly intense ESS neutrino beam, will offer a drastic improvement in the current constraints obtained from existing CE$ν$NS measurements. Finally, we discuss how the ESS has the potential to provide the leading CE$ν$NS-based constraints, complementing also further experimental probes and astrophysical observations.

It has long been pointed out that there are seven different two-zero texture neutrino mass matrices compatible with neutrino oscillation data. We perform an updated analysis with the recently published Nu-Fit 6.0 results. We also subject the seven two-zero textures to constraints on neutrino mass from cosmology, end point of beta decay spectrum, and neutrinoless double beta decay experiments. We find that all seven textures are compatible with the new oscillation parameters. However, we find five textures, whose 1-1 entry is nonvanishing, are in severe tension with the constraints from cosmology and neutrinoless double beta decay. With the next generation experiments, these five textures could be decisively ruled out. For the remaining two textures, one of them could be ruled out, or severely constrained, if the octant of $θ_{23}$ is determined.

In the era of precision measurements of neutrino oscillation parameters, it is necessary for experiments to disentangle discrepancies that may indicate physics beyond the Standard Model in the neutrino sector. KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study the oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on the initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photosensors. A high-purity neutrino sample was extracted during 2020 and 2021, corresponding to an exposure of 433 kton-years. This sample is analysed following a binned log-likelihood approach to search for invisible neutrino decay, in a three-flavour neutrino oscillation scenario, where the third neutrino mass state $ν_3$ decays into an invisible state, e.g. a sterile neutrino. The resulting best fit of the invisible neutrino decay parameter is $α_3 = 0.92^{+1.08}_{-0.57}\times 10^{-4}~\mathrm{eV^2}$, corresponding to a scenario with $θ_{23}$ in the second octant and normal neutrino mass ordering. The results are consistent with the Standard Model, within a $2.1\,σ$ interval.

The observation of the Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) process using reactor antineutrinos offers a unique opportunity to probe the Standard Model and explore Beyond the Standard Model scenarios. This study reports on the latest results from the CONUS+ experiment conducted at the Leibstadt nuclear power plant (KKL), Switzerland. The CONUS collaboration reports $395 \pm 106$ events detected from reactor antineutrinos with an exposure of 347 kg$\cdot$days, utilizing high-purity germanium detectors operated at sub-keV thresholds. A $χ^2$-based statistical analysis was performed on these results, incorporating systematic uncertainties. This analysis was used to extract the weak mixing angle, establish a limit on the neutrino magnetic moment, and impose constraints on neutrino non-standard interactions using reactor antineutrinos. The results confirm the potential of CE$ν$NS experiments in the study of fundamental neutrino properties and probing new physics.

Solar neutrinos, generated abundantly by thermonuclear reactions in the solar interior, offer a unique tool for studying astrophysics and particle physics. The observation of solar neutrinos has led to the discovery of neutrino oscillation, a topic currently under active research, and it has been recognized by two Nobel Prizes. In this pedagogical introduction to solar neutrino physics, we will guide readers through several key questions: How are solar neutrinos produced? How are they detected? What is the solar neutrino problem, and how is it resolved by neutrino oscillation? This article also presents a brief overview of the theory of solar neutrino oscillation, the experimental achievements, new physics relevant to solar neutrinos, and the prospects in this field.

For many small-signal particle physics analyses, Wilks' theorem, a simplifying assumption that presumes log-likelihood asymptotic normality, does not hold. The most common alternative approach applied in particle physics is a highly computationally expensive procedure put forward by Feldman and Cousins. When many experiments are combined for a global fit to data, deviations from Wilks' theorem are exacerbated, and Feldman-Cousins becomes computationally intractable. We present a novel, machine learning-based procedure that can approximate a full-fledged Bayesian analysis 200 times faster than the Feldman-Cousins method. We demonstrate the utility of this novel method by performing a joint analysis of electron neutrino/antineutrino disappearance data within a single sterile neutrino oscillation framework. Although we present a prototypical simulation-based inference method for a sterile neutrino global fit, we anticipate that similar procedures will be useful for global fits of all kinds, especially those in which Feldman-Cousins is too computationally expensive to use.

The three-flavor neutrino oscillation model describes the well-studied phenomenon of neutrinos produced in association with one charged lepton: electron, muon, or tau, and then later detected in association with a possibly different charged lepton. While somewhat surprising, the firm experimental discovery of the phenomenon in the late 1990s and early 2000s has lead to a revolution in particle physics as the nature of neutrinos has been explored with heightened vigor ever since. At the core of the phenomenon are the six neutrino oscillation parameters. These parameters are fundamental and not predicted from anything else in our model of particle physics. At the time of writing this chapter, many of them have been measured, but several key questions remain that are to be answered by neutrino oscillations themselves. These questions have motivated some of the largest and most involved particle physics experiments built to date. This chapter will develop the basics of neutrino oscillation theory and build intuition for the role of the oscillation parameters and how they are measured, as well as the important role of the matter effect in neutrino oscillations.

We propose two medium-baseline, kiloton-scale neutrino experiments to study neutrinos from LHC proton-proton collisions: SINE, a surface-based scintillator panel detector observing muon neutrinos from the CMS interaction point, and UNDINE, a water Cherenkov detector submerged in lake Geneva observing all-flavor neutrinos from LHCb. Using a Monte Carlo simulation, we estimate millions of neutrino interactions during the high-luminosity LHC era. We show that these datasets can constrain neutrino cross sections, charm production in $pp$ collisions, and strangeness enhancement as a solution to the cosmic-ray muon puzzle. SINE and UNDINE thus offer a cost-effective medium-baseline complement to the proposed short-baseline forward physics facility.

Neutrino self-interactions beyond the standard model have profound implications in astrophysics and cosmology. In this Letter, we study an uncharted scenario in which one of the three neutrino species has a mass smaller than the temperature of the cosmic neutrino background. This results in a relativistic component that significantly broadens the absorption feature on the astrophysical neutrino spectra, in contrast to the sharply peaked absorption expected in the extensively studied scenarios assuming a fully nonrelativistic cosmic neutrino background. By solving the Boltzmann equations for neutrino absorption and regeneration, we demonstrate that this mechanism provides novel sensitivity to sub-keV mediator masses, well below the traditional $\sim 1$--100 MeV range. Future observations of the diffuse supernova neutrino background with Hyper-Kamiokande could probe coupling strengths down to $g \sim 10^{-8}$, surpassing existing constraints by orders of magnitude. These findings open new directions for discoveries and offer crucial insights into the interplay between neutrinos and the dark sector.

Neutrinos are elementary particles that interact only very weakly with matter. Neutrino experiments are, therefore, usually big, with masses in the multi-tonne range. The thresholdless interaction of coherent elastic scattering of neutrinos on atomic nuclei leads to greatly enhanced interaction rates, which allows for much smaller detectors. The study of this process gives insights into physics beyond the Standard Model of particle physics. The CONUS+ experiment was designed to first detect elastic neutrino-nucleus scattering in the fully coherent regime with low-energy neutrinos produced in nuclear reactors. For this purpose, semi-conductor detectors based on high-purity germanium crystals with extremely low-energy thresholds were developed. Here we report the first observation of a neutrino signal with a statistical significance of 3.7 sigma from the CONUS+ experiment, operated at the nuclear power plant in Leibstadt, Switzerland. In 119 days of reactor operation (395$\pm$106) neutrinos were measured compared with a predicted number from calculations assuming Standard Model physics of (347$\pm$59) events. With increased precision, there is potential for fundamental discoveries in the future. The CONUS+ results in combination with other measurements of this interaction channel might therefore mark a starting point for a new era in neutrino physics.

Solar neutrino flux constraints from the legacy GALLEX/GNO and SAGE experiments continue to influence contemporary global analyses of neutrino properties. The constraints depend on the neutrino absorption cross sections for various solar sources. Following recent work updating the $^{51}$Cr and $^{37}$Ar neutrino source cross sections, we reevaluate the $^{71}$Ga solar neutrino cross sections, focusing on contributions from transitions to $^{71}$Ge excited states, but also revising the ground-state transition to take into account new $^{71}$Ge electron-capture lifetime measurements and various theory corrections. The excited-state contributions have been traditionally taken from forward-angle $(p,n)$ cross sections. Here we correct this procedure for the $\approx 10\%-20\%$ tensor operator contribution that alters the relationship between Gamow-Teller and $(p,n)$ transition strengths. Using state-of-the-art nuclear shell-model calculations to evaluate this correction, we find that it lowers the $^8$B and hep neutrino cross sections. However, the addition of other corrections, including contributions from near-threshold continuum states that radiatively decay, leads to an overall increase in the $^8$B and hep cross sections of $\approx 10\%$ relative to the values recommended by Bahcall. Uncertainties are propagated using Monte Carlo simulations.

We report the limits on the diffuse supernova neutrino background (DSNB) flux and the fundamental DSNB parameters measured from the first science run of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon detector located at the Sanford Underground Research Facility in Lead, South Dakota, USA. This is the first time the DSNB limit is measured through the process of the coherent elastic neutrino-nucleus scattering (CE$ν$NS). Using an exposure of 60~live days and a fiducial mass of 5.5~t, the upper limit on the DSNB $ν_x$ (each of $ν_μ$, $ν_τ$, $\barν_μ$, $\barν_τ$) flux is $686-826$~cm$^{-2}$s$^{-1}$ at the 90\% confidence level for neutrino energies E$>$19.3~MeV, assuming the flux for each $ν_x$ flavor is the same. The interval accounts for the uncertainty in existing DSNB models. The present result is comparable to the existing best limit and further improvements are expected after collecting data from an estimated 1,000-day exposure in the future.

Muon colliders provide an exciting new direction to expand the energy frontier of particle physics. We point out a new use of these facilities for neutrino and beyond the Standard Model physics using their main detectors. Muon decays along the accelerator rings create an intense and highly collimated neutrino beam that crosses a thin slice of the kt-scale detector. As a result, it would induce an unprecedented number of neutrino interactions, with $\mathcal{O}(10^4)$ events per second for a 10 TeV $μ^+μ^-$ collider. These interactions are highly energetic and possess a distinct timing signature and a large transverse displacement. We discuss promising applications of these events for instrumentation, electroweak, and beyond-the-Standard Model physics. For instance, a sub-percent measurement of the neutrino-electron scattering rate enables new precision measurements of the Weak angle and a novel detection of the neutrino charge radius.

As well known, the cross sections of the resonance and Quasi-Elastic (QE) scattering off nucleons depend on quantities known as form factors that describe the nucleon structure. There are alternative approaches to determine the values of these non-perturbative quantities, some of them relying on the Neutral Current (NC) scattering of neutrinos off nucleons. In the presence of NC Non-Standard Interactions (NSI), such derivations must be revisited. The aim of the present paper is to discuss how information on NSI can be extracted by combining alternative approaches for deriving the form factors. We discuss how the KamLAND atmospheric neutrino data with $E_ν<{\rm GeV}$ (used to determine the axial strange form factor $g_A^s$) can already constrain the axial NSI of $ν_τ$ with nucleons. We also argue that if the precision measurement of $ν_μ$ NC QE scattering establishes unexpectedly large vector strange form factor ({\it e.g.,} $F_1^s(Q^2)\sim 0.01$), it will be an indication for nonzero NSI coupling with $u$ and $d$ quarks ($ε_{μμ}^{Au/d}\sim 0.01$). We study the QE and resonance scattering cross sections of $ν_τ$ and $ν_e$ off Argon and show that if their axial NSI is of the order of (but of course below) the present bounds, the deviation of QE cross sections from the SM prediction will be sizable and distinct from the uncertainties induced by the form factors.

We investigate the impact of matter effects on T (time-reversal)-odd observables, making use of the quantum-mechanical formalism of neutrino-flavor evolution. We attempt to be comprehensive and pedagogical. Matter-induced T-invariance violation (TV) is qualitatively different from, and more subtle than, matter-induced CP (charge-parity)-invariance violation. If the matter distribution is symmetric relative to the neutrino production and detection points, matter effects will not introduce any new TV. However, if there is intrinsic TV, matter effects can modify the size of the T-odd observable. On the other hand, if the matter distribution is not symmetric, there is genuine matter-induced TV. For Earth-bound long-baseline oscillation experiments, these effects are small. This remains true for unrealistically-asymmetric matter potentials (for example, we investigate the effects of ''hollowing out'' 50% of the DUNE neutrino trajectory). More broadly, we explore consequences, or lack thereof, of asymmetric matter potentials on oscillation probabilities. While fascinating in their own right, T-odd observables are currently of limited practical use, due in no small part to a dearth of intense, well-characterized, high-energy electron-neutrino beams. Further in the future, however, intense, high-energy muon storage rings might become available and allow for realistic studies of T invariance in neutrino oscillations.

Multi-TeV muon colliders offer a powerful means of accessing new physics coupled to muons while generating clean and intense high-energy neutrino beams via muon decays. We study a fixed-target experiment leveraging the neutrino beams and a forward detector pointing at the interaction point of the muon collider. The sensitivity to neutrino self-interactions is analyzed as a feasibility study, focusing on the leptonic scalar $φ$ exclusively coupled to the Standard Model neutrinos. Our work shows that projections from both the main and forward detectors can enhance the existing limits by two orders of magnitude, surpassing other future experiments.

We explore, for the first time, {\textit{neutral-current}} events at long-baseline experiments to constrain vector and axial-vector neutrino non-standard interactions (NSI) with quarks. We leverage the flavor dependence of NSIs to perform an oscillation analysis in the neutral-current channel. We first introduce a framework to parametrize the effect of NSI on the cross section. Then, as an example, we analyze NOvA neutral-current data which provides significantly improved constraints on the axial-vector NSI parameters $\varepsilon_{μμ}^A,~\varepsilon_{ττ}^A$ and $\varepsilon_{eμ}^A$. This is highly complementary to constraints from SNO data, which, differently from long-baseline neutral current data, is not sensitive to isospin conserving NSIs $\varepsilon^A_u=\varepsilon^A_d$. Additionally, we disfavor large values of the diagonal vectorial NSI $\varepsilon_{μμ}^V$ and \varepsilon_{ττ}^V$ which originate from the LMA-Dark solution. We also highlight the complementarity between NSI searches at oscillation experiments using charged current and neutral current channels.

We investigate a neutrino-scalar dark matter (DM) $νφ$ interaction encountering distinctive neutrino sources, namely Diffuse Supernova Neutrino Background (DSNB) and Active Galactic Nuclei (AGN). The interaction is mediated by a fermionic particle $F$, in which the $νφ$ scattering cross section characterizes different energy dependent with respect to the kinematic regions, and manifests itself through the attenuation of neutrino fluxes from these sources. We model the unscattered neutrino flux from DSNB via core-collapse supernova (CCSN) and star-formation rate (SFR), then incorporate the present Super-Kamionkande and future DUNE/Hyper-Kamiokande experiments to set limits on DM-neutrino interaction. For AGNs, NGC 1068 and TXS 0506+056, where the neutrino carries energy above TeV, we select the kinematic region $m^2_F \gg E_νm_φ\gg m^2_φ$ such that the $νφ$ scattering cross section features an enhancement at high energy. Furthermore, taking into account the DM spike profile at the center of AGN, we constrain on $m_φ$ and scattering cross section via computing the neutrino flux at IceCube, where the $φφ^*$ annihilation cross section is implemented to determine the saturation density of the spikes. Notice that the later results heavily rely on the existence of DM spike at the center of AGN, otherwise, our results may alter.

The indirect detection of dark matter (DM) through its annihilation products is one of the primary strategies for DM detection. One of the least constrained classes of models is neutrinophilic DM, because the annihilation products, weakly interacting neutrinos, are challenging to observe. Here, we consider a scenario where MeV-mass DM exclusively annihilates to the third neutrino mass eigenstate, which is predominantly of tau and muon flavor. In such a scenario, the potential detection rate of the neutrinos originating from the DM annihilation in our Galaxy in the conventional detectors would be suppressed by up to approximately two orders of magnitude. This is because the best sensitivity of such detectors for neutrinos with energies below approximately 100 MeV is for electron neutrino flavor. In this work, we highlight the potential of large-scale DM detectors in uncovering such signals in the tens of MeV range of DM masses. In addition, we discuss how coincident signals in direct detection DM experiments and upcoming neutrino detectors such as DUNE, Hyper-Kamiokande, and JUNO could provide new perspectives on the DM problem.

In the $ν$SM extended by adding an eV-scale sterile state, the $(3+1)$ model, the sterile-active level crossing entails the MSW resonance, here referred as the sterile-active (SA) resonance. In this paper, we construct an effective theory of SA resonance which involves only the sterile-active mixing angles and $Δm^2_{41}$, thanks to the given environment of high matter potential which freezes the $ν$SM oscillations. We give our first attempt at an analytic treatment of the effective theory to illuminate the global picture of the SA resonance at a glance. We formulate a perturbative framework in which the structure of ``texture zeros'' of the $S$ matrix in the flavor space and the suppression by the small parameters $\sin θ_{j 4}$ ($j=1,2,3$) allows us to reveal the flavor$-$event-type hierarchy of the resonance-effect strength in the probabilities. We have shown that the cascade events dominantly comes from the three paths through $P(ν_{e} \rightarrow ν_{e})$, $P(\barν_{e} \rightarrow \barν_{e})$, and $P(\barν_μ \rightarrow \barν_τ)$, and a three-component fit is suggested to disentangle the SA resonance generation mechanisms.

We propose the possibility of using the near detector at reactor neutrino experiments to probe the renormalization group (RG) running effect on the leptonic Dirac CP phase $δ_D$. Although the reactor neutrino oscillation cannot directly measure $δ_D$, it can probe the deviation $Δδ\equiv δ_D(Q^2_d) - δ_D(Q^2_p)$ caused by the RG running. Being a key element, the mismatched momentum transfers at neutrino production ($Q^2_p$) and detection ($Q^2_d$) processes can differ by two orders. We illustrate this concept with the upcoming Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) experiment and obtain the projected sensitivity to the CP RG running beta function $β_δ$.

Neutrino oscillation experiments are gradually approaching an era of precision, where subleading effects can also be tested. One such subleading effect is Non-Standard Interactions (NSI), which can play a crucial role in neutrino oscillations. Various works have typically discussed vector NSI in the context of quantum correlations. Recently, there have been improvements in the bounds on scalar NSI as well. In light of these developments, we aim to examine the impact of scalar NSI on quantum correlation measures. To analyze this impact, we are considering the strongest measure of quantum correlation, i.e., non-locality. Our study will encompass both spatial and temporal non-locality measures.

We perform a global analysis of most up-to-date solar neutrino data and KamLAND reactor antineutrino data in the framework of the 3+1 sterile neutrino mixing scenario (invoked to explain the results of the Gallium source experiments) with the aim of quantifying the dependence of the (in)compatibility of the required mixing with assumptions on the initial fluxes. The analysis of solar data is performed in two alternative ways: using the flux predicted by the latest standard solar models, and in a model independent approach where the solar fluxes are also determined by the fit. The dependence on the normalization of the capture rate in the solar Gallium experiments is also quantified. Similarly, in the KamLAND analysis we consider both the case where the reactor flux normalization is assumed to be known a priori, as well as a normalization free case which relies solely on available neutrino data. Using a parameter goodness of fit test, we find that in most cases the compatibility between Gallium and solar+KamLAND data only occur at the $3σ$ level or higher. We also discuss the implications of enforcing better compatibility by tweaking the mechanism for the energy production in the Sun.

We perform a global analysis of most up-to-date solar neutrino data and KamLAND reactor antineutrino data in the framework of the 3+1 sterile neutrino mixing scenario (invoked to explain the results of the Gallium source experiments) with the aim of quantifying the dependence of the (in)compatibility of the required mixing with assumptions on the initial fluxes. The analysis of solar data is performed in two alternative ways: using the flux predicted by the latest standard solar models, and in a model independent approach where the solar fluxes are also determined by the fit. The dependence on the normalization of the capture rate in the solar Gallium experiments is also quantified. Similarly, in the KamLAND analysis we consider both the case where the reactor flux normalization is assumed to be known a priori, as well as a normalization free case which relies solely on available neutrino data. Using a parameter goodness of fit test, we find that in most cases the compatibility between Gallium and solar+KamLAND data only occur at the $3σ$ level or higher. We also discuss the implications of enforcing better compatibility by tweaking the mechanism for the energy production in the Sun.

Recent high-precision cosmological data tighten the bound to neutrino masses and start rising a tension to the results of lab-experiment measurements, which may hint new physics in the role of neutrinos during the structure formation in the universe. A scenario with massless sterile neutrinos was proposed to alleviate the cosmological bound and recover the concordance in the measurements of neutrino masses. We revisit the scenario and discuss its testability at oscillation experiments. We find that the scenario is viable with a large active-sterile mixing that is testable at oscillation experiments. We present a numerical estimation of the sensitivity reach of the IceCube atmospheric neutrino observation to a sterile neutrino with a mass lighter than active neutrinos for the first time. IceCube shows a good sensitivity to the active-sterile mixing at the mass-square difference with a size of $\sim 0.1$ eV$^{2}$ in the case of the \textit{inverted-mass-ordering sterile neutrino}, which is forbidden under the assumption of the standard cosmology but is allowed thanks to the alleviation of the cosmological bound in this scenario.

The cosmological upper bound on the total neutrino mass is the dominant limit on this fundamental parameter. Recent observations-soon to be improved-have strongly tightened it, approaching the lower limit set by oscillation data. Understanding its physical origin, robustness, and model-independence becomes pressing. Here, we explicitly separate for the first time the two distinct cosmological neutrino-mass effects: the impact on background evolution, related to the energy in neutrino masses; and the "kinematic" impact on perturbations, related to neutrino free-streaming. We scrutinize how they affect CMB anisotropies, introducing two effective masses enclosing $\textit{background}$ ($\sum m_ν^\mathrm{Backg.}$) and $\textit{perturbations}$ ($\sum m_ν^\mathrm{Pert.}$) effects. We analyze CMB data, finding that the neutrino-mass bound is mostly a background measurement, i.e., how the neutrino energy density evolves with time. The bound on the "kinematic" variable $\sum m_ν^\mathrm{Pert.}$ is largely relaxed, $\sum m_ν^\mathrm{Pert.} < 0.8\,\mathrm{eV}$. This work thus adds clarity to the physical origin of the cosmological neutrino-mass bound, which is mostly a measurement of the neutrino equation of state, providing also hints to evade such a bound.

The PANDAX-4T and XENONnT experiments present indications of Coherent Elastic Neutrino Nucleus Scattering (CE$ν$NS) from ${}^{8}$B solar neutrinos at 2.6$σ$ and 2.7$σ$, respectively. This constitutes the first observation of the neutrino "floor" or "fog", an irreducible background that future dark matter searches in terrestrial detectors will have to contend with. Here, we first discuss the contributions from neutrino-electron scattering and from the Migdal effect in the region of interest of these experiments, and we argue that they are non-negligible. Second, we make use of the recent PANDAX-4T and XENONnT data to derive novel constraints on light scalar and vector mediators coupling to neutrinos and quarks. We demonstrate that these experiments already provide world-leading laboratory constraints on new light mediators in some regions of parameter space.

A nearby supernova will carry an unprecedented wealth of information about astrophysics, nuclear physics, and particle physics. Because supernova are fundamentally neutrino driven phenomenon, our knowledge about neutrinos -- particles that remain quite elusive -- will increase dramatically with such a detection. One of the biggest open questions in particle physics is related to the masses of neutrinos. Here we show how a galactic supernova provides information about the masses of each of the three mass eigenstates \emph{individually}, at some precision, and is well probed at JUNO. This information comes from several effects including time delay and the MSW effect within the supernova. The time delay feature is strongest during a sharp change in the flux such as the neutronization burst; additional information may also come from a QCD phase transition in the supernova or if the supernova forms a black hole. We consider both standard cases as dictated by local oscillation experiments as well as new physics motivated scenarios where neutrino masses may differ across the galaxy.

Recently, two dark matter direct detection experiments have announced the first indications of nuclear recoils from solar $^8$B neutrinos via coherent elastic neutrino-nucleus scattering (CE$ν$NS) with xenon nuclei. These results constitute a turning point, not only for dark matter searches that are now entering the \textit{neutrino fog}, but they also bring out new opportunities to exploit dark matter facilities as neutrino detectors. We investigate the implications of recent data from the PandaX-4T and XENONnT experiments on both Standard Model physics and new neutrino interactions. We first extract information on the weak mixing angle at low momentum transfer. Then, following a phenomenological approach, we consider Lorentz-invariant interactions (scalar, vector, axial-vector, and tensor) between neutrinos, quarks and charged leptons. Furthermore, we study the $U(1)_\mathrm{B-L}$ scenario as a concrete example of a new anomaly-free vector interaction. We find that despite the low statistics of these first experimental results, the inferred bounds are in some cases already competitive. For the scope of this work we also compute new bounds on some of the interactions using CE$ν$NS data from COHERENT and electron recoil data from XENONnT, LUX-ZEPLIN, PandaX-4T, and TEXONO. It seems clear that while direct detection experiments continue to take data, more precise measurements will be available, thus allowing to test new neutrino interactions at the same level or even improving over dedicated neutrino facilities.

Neutrino self-interaction with a larger ``Fermi constant'' is often resorted to for understanding various puzzles of our universe. We point out that a light, neutrinophilic scalar particle $φ$ through radiative correction leads to an energy-scale dependence in the neutrino-$Z$-boson gauge coupling. The driver behind this phenomenon is a large separation between the mass scales of $φ$ and additional heavy particles needed for gauge invariance. This is a generic effect insensitive to details of the UV completion. We show that the running can change the $Zν\barν$ coupling by several percent and affect the measurement of weak mixing angle through neutrino neutral-current processes. We discuss the interplay between the running of the $Zν\barν$ coupling and $\sin^2θ_W$ in various experimental observables. It is possible to disentangle the two effects with more than one precise measurement.

We investigate a dark matter model that couples to the standard model through a one-loop interaction with neutrinos, where the mediator particles also generate neutrino masses. We perform a global fit that incorporates dark matter relic abundance, primordial nucleosynthesis, neutrino mass, collider and indirect detection constraints. Thanks to the loop suppression, large couplings are allowed, and we find that the model parameters are constrained on all sides. Dark matter masses from 10 MeV to a few TeV are allowed, but sub-GeV masses are preferred for the model to also account for the heaviest neutrino mass. Though our results are valid for a single neutrino mass eigenstate at a time, the model and methods are generalizable to the full 3-flavor case.

Neutrinos are neutral in the Standard Model, but they have tiny charge radii generated by radiative corrections. In theories Beyond the Standard Model, neutrinos can also have magnetic and electric moments and small electric charges (millicharges). We review the general theory of neutrino electromagnetic form factors, which reduce, for ultrarelativistic neutrinos and small momentum transfers, to the neutrino charges, effective charge radii, and effective magnetic moments. We discuss the phenomenology of these electromagnetic neutrino properties and we review the existing experimental bounds. We briefly review also the electromagnetic processes of astrophysical neutrinos and the neutrino magnetic moment portal in the presence of sterile neutrinos.

The interference between the atmospheric and solar neutrino oscillation sub-amplitudes is said to be responsible for CP violation (CPV) in neutrino appearance channels. More precisely, CPV is generated by the interference between the parts of the neutrino oscillation amplitude which are CP even and CP odd: even or odd when the neutrino mixing matrix is replaced with its complex conjugate. This is the CPV interference term, as it gives a contribution to the oscillation probability, the square of the amplitude, which is opposite in sign for neutrinos and anti-neutrinos and is unique. For this interference to be non-zero, at least two sub-amplitudes are required. There are, however, other interference terms, which are even under the above exchange, these are the CP conserving (CPC) interference terms. In this paper, we explore in detail these CPC interference terms and show that they cannot be uniquely defined, as one can move pieces of the amplitude from the atmospheric sub-amplitude to the solar sub-amplitude and vice versa. This freedom allows one to move the CPC interference terms around, but does not let you eliminate them completely. We also show that there is a reasonable definition of the atmospheric and solar sub-amplitudes for the appearance channels such that in neutrino disappearance probability there is no atmospheric-solar CPC interference term. However, with this choice, there is a CPC interference term within the atmospheric sector.

We analyze how neutrino oscillation and coherent elastic neutrino-nucleus scattering data impact the global SMEFT fit. We first review the mapping between the SMEFT parameters and the so-called NSI framework, commonly considered in the neutrino literature. We also present a detailed discussion of how the measurements for the normalization of neutrino fluxes and cross sections, that will also be affected by the new physics, indirectly impact the measured oscillation probabilities. We then analyze two well-motivated simplified scenarios. Firstly, we study a lepton flavour conserving case, usually assumed in global SMEFT analyses, showing the complementarity of neutrino oscillation and CE$ν$NS experiments with other low-energy observables. We find that the inclusion of neutrino data allows to constrain previously unbounded SMEFT operators involving the tau flavour and confirm the improvement of the constraint on a combination of Wilson coefficients previously identified. Moreover, we find that neutrino oscillation constraints on NSI are improved when embedded in the global SMEFT framework. Secondly, we study a lepton flavour violating scenario and find that neutrino data also improves over previously derived global constraints thanks to its sensitivity to new combinations of Wilson coefficients.

We consider an extended seesaw model which generates active neutrino masses via the usual type-I seesaw and leads to a large number of massless fermions as well as a sterile neutrino dark matter (DM) candidate in the $\mathcal{O}(10-100) {\rm~keV}$ mass range. The dark sector comes into thermal equilibrium with Standard Model neutrinos after neutrino decoupling and before recombination via a U(1) gauge interaction in the dark sector. This suppresses the abundance of active neutrinos and therefore reconciles sizeable neutrino masses with cosmology. The DM abundance is determined by freeze-out in the dark sector, which allows avoiding bounds from X-ray searches. Our scenario predicts a slight increase in the effective number of neutrino species $N_{\rm eff}$ at recombination, potentially detectable by future CMB missions.

Current laboratory bounds imply that protons are extremely long-lived. However, this conclusion may not hold for all time and in all of space. We find that the proton lifetime can be $\sim 15$ orders of magnitude shorter in the relatively recent past on Earth, or at the present time elsewhere in the Milky Way. A number of terrestrial and astrophysical constraints are examined and potential signals are outlined. We also sketch possible models that could lead to spatial or temporal variations in the proton lifetime. A positive signal could be compelling evidence for a new long range force of Nature, with important implications for the limitations of fundamental inferences based solely on laboratory measurements.

Lorentz Invariance Violation (LIV) presents an intriguing opportunity to investigate fundamental symmetries, with neutrinos serving as a particularly effective probe for this phenomenon. Long-baseline neutrino experiments, such as the Deep Underground Neutrino Experiment (DUNE), excel at exploring non-isotropic LIV, especially through the observation of sidereal effects. This study comprehensively examines the full parameter space of non-isotropic, non-diagonal LIV parameters with sidereal dependence, focusing on two distinct flux scenarios: a low-energy flux and a tau-optimized flux. Through this analysis, we derive more stringent constraints on LIV parameters. Our results indicate that DUNE may achieve enhanced sensitivity for some LIV parameters, exceeding all previously established limits and marking a significant advancement in the investigation of LIV.

We explore the big-bang nucleosynthesis (BBN) constraint on heavy neutrino that is a mixture of gauge singlet fermion and active neutrinos in the Standard Model. We work in the minimal model with only two parameters, the heavy neutrino mass $m_4$ and the mixing parameter $|U_{a4}|^2$, where $a=e$, $μ$, or $τ$ stands for the active neutrino flavor. We show that both the early universe production mechanism and decay products of the heavy neutrino are determined by $m_4$ and $|U_{a4}|^2$, with little room for further assumptions. This predictivity allows us to present a portrait of the entire BBN excluded parameter space. Our analysis includes various effects including temporary matter domination, energy injections in the form of charged mesons, photons and light neutrinos. The BBN constraint is complementary to terrestrial search for heavy neutrinos (heavy neutral leptons) behind the origin of neutrino masses and portal to the dark sector.

We present an updated global analysis of neutrino oscillation data as of September 2024. The parameters $θ_{12}$, $θ_{13}$, $Δm^2_{21}$, and $|Δm^2_{3\ell}|$ ($\ell = 1,2$) are well-determined with relative precision at $3σ$ of about 13\%, 8\%, 15\%, and 6\%, respectively. The third mixing angle $θ_{23}$ still suffers from the octant ambiguity, with no clear indication of whether it is larger or smaller than $45^\circ$. The determination of the leptonic CP phase $δ_{CP}$ depends on the neutrino mass ordering: for normal ordering the global fit is consistent with CP conservation within $1σ$, whereas for inverted ordering CP-violating values of $δ_{CP}$ around $270^\circ$ are favored against CP conservation at more than $3.6σ$. While the present data has in principle $2.5$--$3σ$ sensitivity to the neutrino mass ordering, there are different tendencies in the global data that reduce the discrimination power: T2K and NOvA appearance data individually favor normal ordering, but they are more consistent with each other for inverted ordering. Conversely, the joint determination of $|Δm^2_{3\ell}|$ from global disappearance data prefers normal ordering. Altogether, the global fit including long-baseline, reactor and IceCube atmospheric data results into an almost equally good fit for both orderings. Only when the $χ^2$ table for atmospheric neutrino data from Super-Kamiokande is added to our $χ^2$, the global fit prefers normal ordering with $Δχ^2 = 6.1$. We provide also updated ranges and correlations for the effective parameters sensitive to the absolute neutrino mass from $β$-decay, neutrinoless double-beta decay, and cosmology.

Scalar Non-Standard Interactions (SNSI) in neutrinos can arise when a scalar mediator couples to both neutrinos and standard model fermions. This beyond the Standard Model (BSM) scenario is particularly interesting as the SNSI contribution appears as a density-dependent perturbation to the neutrino mass, rather than appearing as a matter-induced potential, and the neutrino oscillation probabilities uniquely depend on the absolute neutrino masses. In this work, we show the complex dependence of the SNSI contributions on the neutrino masses and discuss how the mass of the lightest neutrino would regulate any possible SNSI contribution in both mass ordering scenarios. We derive the analytic expressions for neutrino oscillation probabilities, employing the Cayley-Hamilton theorem, in the presence of diagonal elements of SNSI. The expressions are compact and shows explicit dependence on matter effects and the absolute neutrino masses. The analytic expressions calculated here allow us to obtain the dependence of the SNSI contribution on mass terms of the form $m_1 + m_2$, $m_2 - m_1$, $m_1c_{12}^2 + m_2s_{12}^2,$ $ m_1s_{12}^2 + m_2c_{12}^2$, and $m_3$. We then explore the non-trivial impact of neutrino mass ordering on the SNSI contribution. The dependence of the SNSI contribution on the 3$ν$ parameters is then thoroughly explored using our analytic expressions.

The potential of the dark matter direct detection experiments to provide independent measurements on solar neutrino fluxes in the Standard Model and in the presence of the light mediators is studied in this work. We also present the sensitivity of direct detection experiments on light mediators with solar neutrinos. We find that the sensitivities on $^8$B and pp neutrino fluxes can reach $\pm10\%$ with improved backgrounds and systematic uncertainties and they can be further pushed to $\pm3\%$ with a increased exposure. The constraints on light mediators can reach $\mathcal{O}(10^{-6})$ for the masses of scalar and vector mediators below 10 MeV. However, the presence of scalar or vector mediators could lead to shifts in the best fit value of $^8$B fluxes, which will increase the challenges in the precise measurements of solar neutrino fluxes with direct detection experiments.

We show that interactions violating the conservation of lepton numbers in the neutrino sector could significantly alter the standard low entropy picture for the pre-supernova collapsing core of a massive star. A rapid neutrino-antineutrino equilibration leads to entropy generation and enhanced electron capture and, hence, a lower electron fraction than in the standard model. This would affect the downstream core evolution, the prospects for a supernova explosion, and the emergent neutrino signal. If realized by lepton-number-violating neutrino self-interactions (LNV $ν$SI), the relevant mediator mass and coupling ranges can be probed by future accelerator-based experiments.

We show that the Deep Underground Neutrino Experiment (DUNE) has the potential to make a precise measurement of the total active flux of 8B solar neutrinos via neutral-current (NC) interactions with argon. This would complement proposed precise measurements of solar-neutrino fluxes in DUNE via charged-current (CC) interactions with argon and mixed CC/NC interactions with electrons. Together, these would enable DUNE to make a SNO-like comparison of rates and thus to make the most precise measurements of $\sin^2θ_{12}$ and $Δm^2_{21}$ using solar neutrinos. Realizing this potential requires dedicated but realistic efforts to improve DUNE's low-energy capabilities and separately to reduce neutrino-argon cross section uncertainties. Comparison of mixing-parameter results obtained using solar neutrinos in DUNE and reactor antineutrinos in JUNO (Jiangmen Underground Neutrino Observatory) would allow unprecedented tests of new physics.

We scrutinize the potential of upcoming ultra-near reactor neutrino experiments to detect radiative corrections in the elastic neutrino-electron scattering channel, focusing on the JUNO-TAO and CLOUD detectors, which employ advanced scintillator detection technologies. Previous reactor experiments have already constrained the electron neutrino charge radius, which is a neutrino property associated with a certain subset of the total radiative corrections, and have achieved limits that are only about an order of magnitude away from the Standard Model prediction. Our study demonstrates that JUNO-TAO and CLOUD could discover the neutrino charge radius in the near future, considering the established treatment of the charge radius. However, we show that it is necessary to go beyond this standard treatment. By including the complete set of one-loop level radiative corrections, we find a partial cancellation with the charge radius effect, reducing the experimental sensitivity to this quantity. Nevertheless, JUNO-TAO and CLOUD still have the potential to achieve a $5σ$ discovery but over longer timescales within a reasonable operational timeframe.

We investigate the physics potential of the upcoming Deep Underground Neutrino Experiment (DUNE) in probing active-sterile mixing. We present analytic expressions for relevant oscillation probabilities for three active and one sterile neutrino of eV-scale mass and highlight essential parameters impacting the oscillation signals at DUNE. We then explore the space of sterile parameters as well as study their correlations among themselves and with parameters appearing in the standard framework ($δ_{13}$ and $θ_{23}$). We perform a combined fit for the near and far detector at DUNE using GLoBES. We consider alternative beam tune (low energy and medium energy) and runtime combinations for constraining the sterile parameter space. We show that charged current and neutral current interactions over the near and far detector at DUNE allow for an improved sensitivity for a wide range of sterile neutrino mass splittings.

We consider ultralight scalar dark matter that couples to right-handed neutrinos. Due to the high density of neutrinos in the early universe, the background neutrino density dominates the dynamics of the scalar field, and qualitatively alters the field's cosmological evolution. This effect has not been included in previous literature, and changes the interpretation of cosmological data and its interplay with laboratory experiments. To illustrate these points a simplified model of a $1+1$ setup with a single scalar field is analyzed. We find that: {\it i}) The scalar field experiences an asymmetric potential and its energy density redshifts differently than ordinary matter. {\it ii}) Neutrino mass measurements at the CMB and oscillation experiments performed today complement one another (i.e., they constrain different regions of parameter space). {\it iii}) There exists potentially interesting cosmologies with either $O(1)$ variations in the dark matter density between the CMB and today, or $O(1)$ oscillations of neutrino mass.

Neutrinos traveling over cosmic distances are ideal probes of new physics. We leverage on the approaching detection of the diffuse supernova neutrino background (DSNB) to explore whether, if the DSNB showed departures from theoretical predictions, we could attribute such modifications to new physics unequivocally. In order to do so, we focus on visible neutrino decay. Many of the signatures from neutrino decay are degenerate with astrophysical unknowns entering the DSNB modeling. Next generation neutrino observatories, such as Hyper-Kamiokande, JUNO, as well as DUNE, will set stringent limits on a neutrino lifetime over mass ratio $τ/m \sim 10^{9}$-$10^{10}$ s eV$^{-1}$ at $90\%$ C.L., if astrophysical uncertainties and detector backgrounds were to be fully under control. However, if the lightest neutrino is almost massless and the neutrino mass ordering is normal, constraining visible decay will not be realistically possible in the coming few decades. We also assess the challenges of distinguishing among different new physics scenarios (such as visible decay, invisible decay, and quasi-Dirac neutrinos), all leading up to similar signatures in the DSNB. This work shows that the DSNB potential for probing new physics strongly depends on an improved understanding of the experimental backgrounds at next generation neutrino observatories as well as progress in the DSNB modeling.

Scalar non-standard neutrino interactions (sNSI) is a scenario where neutrinos can develop a medium dependent contribution to their mass due to a new scalar mediator. This scenario differs from the commonly discussed vector mediator case in that the oscillation effect scales with density rather than density and neutrino energy. Thus the strongest oscillation constraint comes from solar neutrinos which experience the largest density in a neutrino oscillation experiment. We derive constraints on all the sNSI parameters as well as the absolute neutrino mass scale by combining solar and reactor data and find solar neutrinos to be $>1$ order of magnitude more sensitive to sNSI than terrestrial probes such as long-baseline experiments.

We assess the potential of neutrino telescopes to discover quantum-gravity-induced decoherence effects modeled in the open-quantum system framework and with arbitrary numbers of active and dark fermion generations, such as particle dark matter or sterile neutrinos. The expected damping of neutrino flavor oscillation probabilities as a function of energy and propagation length thus encodes information about quantum gravity effects and the fermion generation multiplicity in the dark sector. We employ a public Monte-Carlo dataset provided by the IceCube Collaboration to model the detector response and estimate the sensitivity of IceCube to oscillation effects in atmospheric neutrinos induced by the presented model. Our findings confirm the potential of very-large-volume neutrino telescopes to test this class of models and indicate higher sensitivities for increasing numbers of dark fermions.

In this paper, we take a close look at the interaction between the TeV--PeV energy astrophysical neutrinos and a hypothetical cosmic sterile-neutrino background. These interactions yield absorption features, also called ``dips", in the astrophysical neutrino spectrum, which are studied using the deposited energy distribution of high-energy starting events (HESE) in the IceCube detector. We improve upon the previous analysis by including the effects of regeneration and a realistic source distribution on the propagation of astrophysical neutrinos. We use the latest 7.5-year HESE dataset and include the observation of Glashow resonance in our analysis. We evaluate the impact of these dips on the inferred spectral index and overall normalization of the astrophysical neutrinos. We find a mild preference for dips in the 300--800 TeV range, and the best-fit parameters for the mass of sterile-neutrino and the mediator are 0.5 eV and 23 MeV, respectively. We find that the inclusion of these absorption features lowers the spectral index of astrophysical neutrinos to $2.60^{+0.19}_{-0.16}$. We show qualitatively that the lower spectral index from HESE sample can reduce the disagreement with the Northern Tracks sample. We also forecast the event spectrum for IceCube-Gen2 for the two different fits.

Among three leptonic mixing angles, $θ_{23}$ angle, which characterizes the fractional contribution of two flavor eigenstates $ν_μ$ and $ν_τ$ to the third mass eigenstate $ν_3$, is known to be the largest but the least precisely measured. The work investigates possible reach of $θ_{23}$ precision with two upcoming gigantic accelerator-based long-baseline neutrino experiments, namely Hyper-Kamiokande and DUNE experiments as well as a possible joint analyses of future neutrino facilities. Our simulation yields that each experiment will definitely establish the octant of $θ_{23}$ angle for all values within 1$σ$ parameter interval, while considering the current limitation. However, if the actual value is $0.48\leq \sin^2θ_{23}\leq 0.54$, it becomes challenging for these two experiments to reject the maximal ($θ_{23}=π/4$) hypothesis and conclude its octant. This octant-blind region can be further explored with the proposed facilities ESSnuSB and a neutrino factory. Accurate determination of the mixing angle $θ_{23}$, as well as the accuracy of $δ_{CP}$, is crucial for examining a certain category of discrete non-Abelian leptonic flavor models. Specifically if CP is conserved in leptonic sector, the combined analysis of Hyper-K and DUNE will rule out the majority of these models. However, if the CP is maximally violated, higher precision of $δ_{CP}$ is necessary for testing these flavor models.

A dark sector with a very large number of massive degrees of freedom is generically constrained by radiative corrections to Newton's constant. However, there are caveats to this statement, especially if the degrees of freedom are light or mass-less. Here, we examine in detail and update a number of constraints on the possible number of dark degrees of freedom, including from black hole evaporation, from perturbations to systems including an evaporating black hole, from direct gravitational production at colliders, from high-energy cosmic rays, and from supernovae energy losses.

Primordial Black Holes (PBHs) are capable of emitting extremely energetic particles independent of their interactions with the Standard Model. In this work, we investigate whether PBHs evaporating in the early universe could be responsible for some of the observed high-energy neutrinos above the TeV or PeV scale in the present universe. We compute the energy spectrum of neutrinos directly emitted by PBHs with a monochromatic mass function and estimate the wash-out point, which determines the maximum energy of the spectrum. We find that the spectrum generally extends to high energies following a power law of $E_ν^{-3}$ until it reaches the wash-out point, which crucially depends on the PBH mass. For PBHs of $10^{13}$ grams, the spectrum can extend up to the PeV scale, though the flux is too low for detection. We also consider an indirect production mechanism involving dark particles that are emitted by PBHs and decay into neutrinos at a much later epoch. This mechanism allows lighter (such as those in the gram to kilogram range) PBHs to produce more energetic neutrino fluxes without being washed out by the thermal plasma in the early universe. In this scenario, we find that ultra-high-energy neutrinos around or above the EeV scale can be generated, with sufficiently high fluxes detectable by current and future high-energy neutrino observatories such as IceCube and GRAND.

The weak mixing angle provides a sensitive test of the Standard Model. We study SBND's sensitivity to the weak mixing angle using neutrino-electron scattering events. We perform a detailed simulation, paying particular attention to background rejection and estimating the detector response. We find that SBND can provide a reasonable constraint on the weak mixing angle, achieving 8% precision for $10^{21}$ protons on target, assuming an overall flux normalization uncertainty of 10%. This result is superior to those of current neutrino experiments and is relatively competitive with other low-energy measurements.

We investigate constraints on neutrino non-standard interactions (NSIs) in the effective field theory framework, using data from the first measurement of solar $^8$B neutrinos via coherent elastic neutrino-nucleus scattering (CE$ν$NS) in the PandaX-4T and XENONnT experiments and data from the COHERENT experiment. The impacts of neutrino NSIs on the CE$ν$NS cross section and the matter effect in the propagation of solar neutrinos are included, while we obtain that the expected number of CE$ν$NS events is more sensitive to neutrino NSIs appearing in the cross section. Due to relatively large statistical uncertainties, the sensitivities of the PandaX-4T and XENONnT experiments to the neutrino NSIs are currently limited, compared to the COHERENT experiment. Besides, we find that since the central value of the measured CE$ν$NS counts significantly differs from the Standard Model prediction, the sensitivity of PandaX-4T experiment is even more restricted compared to XENONnT. However, the measurements of PandaX-4T and XENONnT are uniquely sensitive to the neutrino NSIs for the $τ$ flavor due to oscillation feature of the solar $^8$B neutrinos. We also assess how the experimental central value, exposure, and systematic uncertainties will affect the constraints on neutrino NSIs from various CE$ν$NS measurements in the future.

Proton-proton collisions at energy-frontier facilities produce an intense flux of high-energy light particles, including neutrinos, in the forward direction. At the LHC, these particles are currently being studied with the far-forward experiments FASER/FASER$ν$ and SND@LHC, while new dedicated experiments have been proposed in the context of a Forward Physics Facility (FPF) operating at the HL-LHC. Here we present a first quantitative exploration of the reach for neutrino, QCD, and BSM physics of far-forward experiments integrated within the proposed Future Circular Collider (FCC) project as part of its proton-proton collision program (FCC-hh) at $\sqrt{s} \simeq 100$ TeV. We find that $10^9$ electron/muon neutrinos and $10^7$ tau neutrinos could be detected, an increase of several orders of magnitude compared to (HL-)LHC yields. We study the impact of neutrino DIS measurements at the FPF@FCC to constrain the unpolarised and spin partonic structure of the nucleon and assess their sensitivity to nuclear dynamics down to $x \sim 10^{-9}$ with neutrinos produced in proton-lead collisions. We demonstrate that the FPF@FCC could measure the neutrino charge radius for $ν_{e}$ and $ν_μ$ and reach down to five times the SM value for $ν_τ$. We fingerprint the BSM sensitivity of the FPF@FCC for a variety of models, including dark Higgs bosons, relaxion-type scenarios, quirks, and millicharged particles, finding that these experiments would be able to discover LLPs with masses as large as 50 GeV and couplings as small as $10^{-8}$, and quirks with masses up to 10 TeV. Our study highlights the remarkable opportunities made possible by integrating far-forward experiments into the FCC project, and it provides new motivation for the FPF at the HL-LHC as an essential precedent to optimize the forward physics experiments that will enable the FCC to achieve its full physics potential.

PandaX-4T and XENONnT have recently reported the first measurement of nuclear recoils induced by the $^8$B solar neutrino flux, through the coherent elastic neutrino-nucleus scattering (CE$ν$NS) channel. As long anticipated, this is an important milestone for dark matter searches as well as for neutrino physics. This measurement means that these detectors have reached exposures such that searches for low mass, $\lesssim 10$ GeV dark matter cannot be analyzed using the background-free paradigm going forward. It also opens a new era for these detectors to be used as neutrino observatories. In this paper we assess the sensitivity of these new measurements to new physics in the neutrino sector. We focus on neutrino non-standard interactions (NSI) and show that -- despite the still moderately low statistical significance of the signals -- these data already provide valuable information. We find that limits on NSI from PandaX-4T and XENONnT measurements are comparable to those derived using combined COHERENT CsI and LAr data, as well as those including the latest Ge measurement. Furthermore, they provide sensitivity to pure $τ$ flavor parameters that are not accessible using stopped-pion or reactor sources. With further improvements of statistical uncertainties as well as larger exposures, forthcoming data from these experiments will provide important, novel results for CE$ν$NS-related physics.

In neutrino experiments sensitive to multiple flavors, the analyzers may be presented with a choice of treating the uncertainties on the respective cross sections in a correlated or an uncorrelated manner. This study focuses on the charged current deep inelastic scattering (CC DIS) channel in experiments sensitive to both muon and tau neutrinos. We evaluate the ratio of the leading-order $ν_τ$ and $ν_μ$ cross sections and derive its uncertainty from the underlying parton distribution functions (PDFs). We find that, for neutrino energies above 5 GeV, the PDF-driven uncertainty on the cross section ratio is less than 3%, with a larger (2-30%) variation seen in antineutrinos at energies below 10 GeV. These results suggest that for atmospheric tau neutrino appearance analyses, the uncertainties in $ν_τ$ and $ν_μ$ DIS cross sections should be coupled, while separate treatment for the two flavors may be warranted in long-baseline experiments with an antineutrino beam. We further explore the role of the invariant hadronic mass threshold defining the onset of the DIS regime. We argue that its impact may be incorporated only if it is applied to both DIS and resonance cross sections, and if the correlations with other DIS and resonance cross section parameters are taken into account.

New heavy neutral leptons lead to non-unitary effects in models for neutrino masses. Such effects could represent a sign of new physics beyond the Standard Model, leading to observable deviations in neutrino oscillation experiments, lepton flavor violation, and other precision measurements. This work explores the parameter space of the linear and inverse low-scale seesaw models based on flavor symmetries consistent with neutrino oscillation experiments. In particular, we investigated the violation of unitarity when the lepton flavor violation is absent and when only one lepton flavor-violating channel is present.

A high-precision measurement of $Δm^2_{31}$ and $θ_{23}$ is inevitable to estimate the Earth's matter effect in long-baseline experiments which in turn plays an important role in addressing the issue of neutrino mass ordering and to measure the value of CP phase in $3ν$ framework. After reviewing the results from the past and present experiments, and discussing the near-future sensitivities from the IceCube Upgrade and KM3NeT/ORCA, we study the expected improvements in the precision of 2-3 oscillation parameters that the next-generation long-baseline experiments, DUNE and T2HK, can bring either in isolation or combination. We highlight the relevance of the possible complementarities between these two experiments in obtaining the improved sensitivities in determining the deviation from maximal mixing of $θ_{23}$, excluding the wrong-octant solution of $θ_{23}$, and obtaining high precision on 2-3 oscillation parameters, as compared to their individual performances. We observe that for the current best-fit values of the oscillation parameters and assuming normal mass ordering (NMO), DUNE + T2HK can establish the non-maximal $θ_{23}$ and exclude the wrong octant solution of $θ_{23}$ at around 7$σ$ C.L. with their nominal exposures. We find that DUNE + T2HK can improve the current relative 1$σ$ precision on $\sin^{2}θ_{23}~(Δm^{2}_{31})$ by a factor of 7 (5) assuming NMO. Also, we notice that with less than half of their nominal exposures, the combination of DUNE and T2HK can achieve the sensitivities that are expected from these individual experiments using their full exposures. We also portray how the synergy between DUNE and T2HK can provide better constraints on ($\sin^2θ_{23}$ - $δ_{\mathrm{CP}}$) plane as compared to their individual reach.

In this work, we explore the effect of neutrino nonstandard interactions (NSI) involving the charm quark at SND@LHC. Using an effective description of new physics in terms of four-fermion operators involving a charm quark, we constrain the Wilson coefficients of the effective interaction from two and three-body charmed meson decays. In our fit, we include charmed meson decays not only to pseudoscalar final states but also to vector final states and include decays to the $η$ and $η^\prime$ final states. We also consider constraints from charmed baryon decays. We then study the effect of new physics in neutrino scattering processes, involving charm production at SND@LHC, for various benchmark new physics couplings obtained from the low energy fits. Finally, we also study the effects of lepton universality violation (LUV) assuming that the new physics coupling is not lepton universal.

We consider the time reversal (T) transformation in neutrino oscillations in a model-independent way by comparing the observed transition probabilities at two different baselines at the same neutrino energy. We show that, under modest model assumptions, if the transition probability $P_{ν_μ\toν_e}$ around $E_ν\simeq 0.86$ GeV measured at DUNE is smaller than the one at T2HK the T symmetry has to be violated. Experimental requirements needed to achieve good sensitivity to this test for T violation are to obtain enough statistics at DUNE for $E_ν\lesssim 1$ GeV (around the 2nd oscillation maximum), good energy resolution (better than 10%), and near-detector measurements with a precision of order 1% or better.

We analyze data from the CsI, liquid Ar and Ge detectors of the COHERENT experiment and confirm within $1.5σ$ that the measured elastic neutrino-nucleus scattering cross section is proportional to the square of the number of neutrons in the nucleus, as expected for coherent scattering in the standard model. We also show how various degeneracies involving nonstandard neutrino interaction parameters are broken in a combined analysis of the three datasets.

This study presents a comprehensive model for neutrino deep inelastic scattering (DIS) cross sections spanning energies from 50 GeV to 5$\times10^{12}$ GeV with an emphasis on applications to neutrino telescopes. We provide calculations of the total charged-current DIS cross sections and inelasticity distributions up to NNLO for isoscalar nucleon targets and up to NLO order for nuclear targets. Several modifications to the structure functions are applied to improve the modeling of the cross sections at low energies where perturbative QCD is less accurate and at high energies where there is non-negligible top quark production, and small-$x$ logarithms need to be resumed. Using the FONLL general-mass variable-flavor number scheme, we account for heavy quark mass effects and separate the heavy flavor components of the structure functions, obtaining predictions of their relative contributions to the cross sections and the uncertainties arising from the parton distribution functions. Additionally, the effects of final state radiation are implemented in the calculation of the double-differential cross section and discussed in terms of their impact on measurements at neutrino telescopes.

We outline a fundamentally quantum description of bosonic dark matter (DM) from which the conventional classical-wave picture emerges in the limit $m \ll 10~\textrm{eV}$. As appropriate for a quantum system, we start from the density matrix which encodes the full information regarding the possible measurements we could make of DM and their fluctuations. Following fundamental results in quantum optics, we argue that for DM it is most likely that the density matrix takes the explicitly mixed form of a Gaussian over the basis of coherent states. Deviations from this would generate non-Gaussian fluctuations in DM observables, allowing a direct probe of the quantum state of DM. Our quantum optics inspired approach allows us to rigorously define and interpret various quantities that are often only described heuristically, such as the coherence time or length. The formalism further provides a continuous description of DM through the wave-particle transition, which we exploit to study how density fluctuations over various physical scales evolve between the two limits and to reveal the unique behavior of DM near the boundary of the wave and particle descriptions.

We systematically assess the DUNE experiment's ability to distinguish between various beyond-standard neutrino oscillation hypotheses pair combinations. For a pair comparison, we evaluate the statistical separation, where one hypothesis plays the role of the true signal while the other corresponds to the test signal. The beyond-standard neutrino oscillation hypotheses under scrutiny include neutrino decay (invisible and visible), non-standard interactions, quantum decoherence, and the violation of the equivalence principle. When taken as the true model, we found that either quantum decoherence or the violation of the equivalence principle are the easiest to differentiate compared to the rest of the hypotheses. Additionally, from our statistical test, we investigate potential discrepancies between the measured CP-violation phase $δ_{CP}$ relative to its true value, which could occur for a given comparison. In our analysis, we will take the true values of $δ_{CP}$ as $-90^\circ$ and $180^\circ$. Notably, even in cases where the beyond-standard neutrino oscillation hypotheses scenarios are statistically indistinguishable, the measured value can exhibit significant deviations from its true value.

The bounds on parameters of the eV and higher scale sterile neutrinos from the $0νββ$ decay have been refined and updated. We present a simple and compact analytic expression for the bound in the $Δm^2_{41} - \sin^2 2θ_{14}$ plane, which includes all relevant parameters. Dependencies of the bound on unknown CP-phases and the type of mass spectrum of light neutrinos (mass ordering and level of degeneracy) are studied in detail. We have computed the bounds using the latest and most stringent data from KamLAND-Zen. The projected constraints from future experiments are estimated. The obtained bounds are confronted with positive indications of the presence of sterile neutrinos as well as with the other existing bounds. The $0νββ$ decay results exclude the regions of parameters implied by BEST and Neutrino-4, and the regions indicated by LSND and MiniBooNE are in conflict with $0νββ$ results combined with $ν_μ-$ disappearance bounds.

We study the kinetic cooling (heating) of old neutron stars due to coherent scattering with relic neutrinos (sterile neutrino dark matter) via Standard Model neutral-current interactions. We take into account several important physical effects, such as gravitational clustering, coherent enhancement, neutron degeneracy and Pauli blocking. We find that the anomalous cooling of nearby neutron stars due to relic neutrino scattering might actually be observable by current and future telescopes operating in the optical to near-infrared frequency band, such as the James Webb Space Telescope (JWST), provided there is a large local relic overdensity that is still allowed. Similarly, the anomalous heating of neutron stars due to coherent scattering with keV-scale sterile neutrino dark matter, could also be observed by JWST or future telescopes, which would probe hitherto unexplored parameter space in the sterile neutrino mass-mixing plane.

While the origin of neutrino masses remains unknown, several key neutrino mass generation models result in a non-unitary three-neutrino mixing matrix. To put such models to test, the deviations of the mixing matrix from unitarity can be measured directly through neutrino oscillation experiments. In this study, we perform a Bayesian analysis of the non-unitary mixing model using the recent public data from atmospheric and reactor neutrino experiments - namely IceCube-DeepCore, Daya Bay, and KamLAND. The novelty of our approach compared to the preceding global fits for non-unitarity is in the detailed treatment of the atmospheric neutrino data, which for the first time includes the relevant flux and detector systematic uncertainties. From the Bayesian posteriors on the individual mixing matrix elements, we derive the non-unitarity constraints in the form of normalisations and closures of the mixing matrix rows and columns, assuming either a fully unconstrained matrix or a physically motivated submatrix scenario. We find comparable constraints for electron and tau row normalisations as other similar studies in literature, and additionally reveal strong correlations between muon and tau row constraints induced by the atmospheric systematic uncertainties. We find that the current data is well described by both unitary and non-unitary mixing models, with a strong preference for the unitary mixing indicated by the Bayes factor. With the upcoming IceCube-Upgrade and JUNO detectors, both featuring superior energy resolution compared to the current atmospheric and reactor neutrino experiments, our constraints on the row normalisations in the submatrix case are expected to improve by 25%, 40%, and 20% in the electron, muon, and tau sectors respectively.

An ultralight gauge boson could address the missing cosmic dark matter, with its transverse modes contributing to a relevant component of the galactic halo today. We show that, in the presence of a coupling between the gauge boson and neutrinos, these transverse modes affect the propagation of neutrinos in the galactic core. Neutrinos emitted from galactic or extra-galactic supernovae could be delayed by $δt = \left(10^{-8}-10^1\right)\,$s for the gauge boson masses $m_{A'} = \left(10^{-23}-10^{-19}\right)\,$eV and the coupling with the neutrino $g= 10^{-27}-10^{-20}$. While we do not focus on a specific formation mechanism for the gauge boson as the dark matter in the early Universe, we comment on some possible realizations. We discuss model-dependent current bounds on the gauge coupling from fifth-force experiments, as well as future explorations involving supernovae neutrinos. We consider the concrete case of the DUNE facility, where the coupling can be tested down to $g \simeq 10^{-27}$ for neutrinos coming from a supernova event at a distance $d = 10\,$kpc from Earth.

DUNE is a next-generation long-baseline neutrino oscillation experiment. It is expected to measure with an unprecedent precision the atmospheric oscillation parameters, including the CP-violating phase $δ_{CP}$. Moreover, several studies have suggested that its unique features should allow DUNE to probe several new physics scenarios. In this work, we explore the performances of the DUNE far detector in constraining new physics if a high-energy neutrino flux is employed (HE-DUNE). We take into account three different scenarios: Lorentz Invariance Violation (LIV), Long Range Forces (LRF) and Large Extra Dimensions (LED). Our results show that HE-DUNE should be able to set bounds competitive to the current ones and, in particular, it can outperform the standard DUNE capabilities in constraining CPT-even LIV parameters and the compactification radius $R_{ED}$ of the LED model.

Neutrino flavor oscillations and conversion in an interacting background (MSW effects) may reveal the charge-parity violation in the next generation of neutrino experiments. The usual approach for studying these effects is to numerically integrate the Schrodinger equation, recovering the neutrino mixing matrix and its parameters from the solution. This work suggests using the classical Jacobi's diagonalization in combination with a reordering procedure to produce a new algorithm, the Sequential Jacobi Diagonalization. This strategy separates linear algebra operations from numerical integration, allowing physicists to study how the oscillation parameters are affected by adiabatic MSW effects in a more efficient way. The mixing matrices at every point of a given parameter space can be stored for speeding up other calculations, such as model fitting and Monte Carlo productions. This approach has two major computation advantages, namely: being trivially parallelizable, making it a suitable choice for concurrent computation, and allowing for quasi-model-independent solutions that simplify Beyond Standard Model searches.

The neutrino oscillation experiments are setting increasingly strong upper bounds on the vector Non-Standard neutrino Interactions (NSI) with matter fields. However, the bounds on the axial NSI are more relaxed, raising the hope that studying the neutral current events at an experiment such as DUNE can give a glimpse on new physics. We build a model that gives rise to axial NSI with large couplings leading to observable deviation from the standard prediction at DUNE. The model is based on a $U(1)$ gauge symmetry with a gauge boson of mass $\sim 30$~GeV which can be discovered at the high luminosity LHC. Combining the LHC and DUNE discoveries, we can unravel the axial form of interaction. The cancellation of anomalies of the gauge group suggests new heavy quarks as well as a dark matter candidate. The new quarks mixed with the first generation quarks can also be discovered at the LHC. Moreover, they provide a seesaw mechanism that explains the smallness of the $u$ and $d$ quark masses. The dark matter has an axial coupling to the quarks which makes its discovery via spin dependent direct dark matter search experiments possible.

Dark photons coupling to $L_μ-L_τ$ lepton number difference are a highly studied light dark matter candidate, with potential to be discovered through their impact on terrestrial neutrino oscillation experiments. We re-examine this in the light of claimed tensions between the NO$ν$A and T2K long baseline experiments, also taking into account data from the MINOS experiment. We obtain leading limits on the $L_μ-L_τ$ gauge coupling $g'$ versus dark photon mass $m_{A'}$, and find no statistically significant alleviation of the tension from inclusion of the new physics effect.

The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar $^8$B neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (0.33 keV) nuclear recoil energy. Combining the commissioning run and the first science run of PandaX-4T, a total exposure of 1.20 and 1.04 tonne$\cdot$year are collected for the paired and US2, respectively. After unblinding, 3 and 332 events are observed with an expectation of 2.8$\pm$0.5 and 251$\pm$32 background events, for the paired and US2 data, respectively. A combined analysis yields a best-fit $^8$B neutrino signal of 3.5 (75) events from the paired (US2) data sample, with $\sim$37\% uncertainty, and the background-only hypothesis is disfavored at 2.64$σ$ significance. This gives a solar $^8$B neutrino flux of ($8.4\pm3.1$)$\times$10$^6$ cm$^{-2}$s$^{-1}$, consistent with the standard solar model prediction. It is also the first indication of solar $^8$B neutrino ``fog'' in a dark matter direct detection experiment.

We investigate the flavor-specific properties of leptophilic dark matter in neutrino mass models, where dark matter signals are directly correlated with the neutrino oscillation data, providing complementary insights into the neutrino mass hierarchy and CP phases. Notably, this can be accomplished without introducing a flavor-specific portal to dark matter, imposing any new flavor symmetry, or involving flavon fields. As a case study, we analyze the correlation between the flavor-philic nature of dark matter and neutrino oscillation data in the type-II seesaw and Zee-Babu models, and extend this discussion to other neutrino mass models. We analyze the indirect signatures of such leptophilic dark matter, specifically examining the spectrum of the cosmic ray electron/positron flux resulting from the pair annihilation of dark matter in the Galactic halo, and explore correlated lepton-specific signals at collider experiments sensitive to neutrino oscillation data.

We show that non-standard neutrino interactions (NSI) can notably modify the pattern of resonant flavor conversion of neutrinos within supernovae and significantly impact the neutronization burst signal in forthcoming experiments such as the Deep Underground Neutrino Experiment (DUNE). The presence of NSI can invert the energy levels of neutrino matter eigenstates and even induce a new resonance in the inner parts close to the proto-neutron star. We demonstrate how DUNE can use these new configurations of energy levels to have sensitivity to NSIs down to $\mathcal{O}(0.1)$. We also elucidate how the effect may result in a puzzling confusion of normal and inverted mass orderings by highlighting the emergence or vanishing of the neutronization peak, which distinguishes between the two mass orderings. Potential implications are analyzed thoroughly.

We study the possibility of measuring T (time reversal) violation in a future long baseline neutrino oscillation experiment. By assuming a neutrino factory as a staging scenario of a muon collider at the J-PARC site, we find that the $ν_e \to ν_μ$ oscillation probabilities can be measured with a good accuracy at the Hyper-Kamiokande detector. By comparing with the probability of the time-reversal process, $ν_μ \to ν_e$, measured at the T2K/T2HK experiments, one can determine the CP phase $δ$ in the neutrino mixing matrix if $| \sin(δ)|$ is large enough. The determination of $δ$ can be made with poor knowledge of the matter density of the earth as T violation is almost insensitive to the matter effects. The comparison of CP and T-violation measurements, ${\it à\ la}$ the CPT theorem, provides us with a non-trivial check of the three neutrino paradigm based on the quantum field theory.

In this paper, we examine the possibility that massive neutrinos are unstable due to their invisible decays $ν^{}_i \to ν^{}_j + φ$, where $ν^{}_i$ and $ν^{}_j$ (for $i, j = 1, 2, 3$) are any two of neutrino mass eigenstates with masses $m^{}_i > m^{}_j$ and $φ$ is a massless Nambu-Goldstone boson, and explore the implications for the detection of cosmological relic neutrinos in the present Universe. First, we carry out a complete calculation of neutrino decay rates in the general case where the individual helicities of parent and daughter neutrinos are specified. Then, the invisible decays of cosmological relic neutrinos are studied and their impact on the capture rates on the beta-decaying nuclei (e.g., $ν^{}_e + {^3{\rm H}} \to {^3{\rm He}} + e^-$) is analyzed. The invisible decays of massive neutrinos could substantially change the capture rates in the PTOLEMY-like experiments when compared to the case of stable neutrinos. In particular, we find that the helicity-changing decays of Dirac neutrinos play an important role whereas those of Majorana neutrinos have no practical effects. However, if a substantial fraction of heavier neutrinos decay into the lightest one, the detection of relic neutrinos will require a much higher energy resolution and thus be even more challenging.

We perform a detailed study of neutrino-electron elastic scattering using the mono-energetic $^{7}$Be neutrinos in Borexino, with an emphasis on exploring the differences between the contributions of $ν_e$, $ν_μ$, and $ν_τ$. We find that current data are capable of measuring these components such that the contributions from $ν_μ$ and $ν_τ$ cannot be zero, although distinguishing between them is challenging -- the differences stemming from Standard Model radiative corrections are insufficient without significantly more precise measurements. In studying these components, we compare predicted neutrino-electron scattering event rates within the Standard Model (accounting for neutrino oscillations), as well as going beyond the Standard Model in two ways. We allow for non-unitary evolution to modify neutrino oscillations, and find that with a larger exposure (${\sim}30$x), Borexino may provide relevant information for constraining non-unitarity, and that JUNO may be able to accomplish this with its data collection of $^{7}$Be neutrinos. We also consider novel $ν_μ$- and $ν_τ$-electron scattering from a gauged $U(1)_{L_μ- L_τ}$ model, showing consistency with previous analyses of Borexino and this scenario, but also demonstrating the impact of uncertainties on Standard Model mixing parameters on these results.

The next generation of neutrino oscillation experiments, JUNO, DUNE, and HK, are under construction now and will collect data over the next decade and beyond. As there are no approved plans to follow up this program with more advanced neutrino oscillation experiments, we consider here one option that had gained considerable interest more than a decade ago: a neutrino factory. Such an experiment uses stored muons in a racetrack configuration with extremely well characterized decays reducing systematic uncertainties and providing for more oscillation channels. Such a machine could also be one step towards a high energy muon collider program. We consider a long-baseline configuration to SURF using the DUNE far detectors or modifications thereof, and compare the expected sensitivities of the three-flavor oscillation parameters to the anticipated results from DUNE and HK. We show optimal beam configurations, the impact of charge identification, the role of statistics and systematics, and the expected precision to the relevant standard oscillation parameters in different DUNE vs.~neutrino factory configurations.

Direct detection is a powerful means of searching for particle physics evidence of dark matter (DM) heavier than about a GeV with $\mathcal O(kiloton)$ volume, low-threshold detectors. In many scenarios, some fraction of the DM may be boosted to large velocities enhancing and generally modifying possible detection signatures. We investigate the scenario where 100% of the DM is boosted at the Earth due to new attractive long-range forces. This leads to two main improvements in detection capabilities: 1) the large boost allows for detectable signatures of DM well below a GeV at large-volume neutrino detectors, such as DUNE, Super-K, Hyper-K, and JUNO, as possible DM detectors, and 2) the flux at the Earth's surface is enhanced by a focusing effect. In addition, the model leads to a significant anisotropy in the signal with the DM flowing dominantly vertically at the Earth's surface instead of the typical approximately isotropic DM signal. We develop the theory behind this model and also calculate realistic constraints using a detailed GENIE simulation of the signal inside detectors.

In this work we analyze the scenario where a MeV scale $L_μ- L_τ$ gauge boson can explain the deficit in the diffuse ultra high energy (UHE) astrophysical neutrino spectrum observed in IceCube, as well as the discrepancy between experimental and $e^+e^-$ dispersion data driven SM calculations of the muon anomalous magnetic moment. We map the parameter space of the model where the elastic resonant s-channel scattering of UHE neutrinos with the cosmic neutrino background, mediated by the new Z', can improve the description of the observed cascade and track spectra over the no-scattering hypothesis. Comparing to recent NA64$μ$ results, we find that some part of the parameter space remains unexplored, but at a data volume of $10^{11}$ muons on target NA64$μ$ will completely probe this region.

Binary neutron star (BNS) mergers can be sources of ultrahigh-energy (UHE) cosmic rays and potential emitters of UHE neutrinos. The upcoming and current radio neutrino detectors like the Giant Radio Array for Neutrino Detection (GRAND), IceCube-Gen2 Radio, and the Radio Neutrino Observatory in Greenland (RNO-G) are projected to reach the required sensitivities to search for these neutrinos. In particular, in conjunction with the next-generation of gravitational wave (GW) detectors like Cosmic Explorer (CE) and Einstein Telescope (ET), GW-triggered stacking searches can be performed with the UHE neutrino detectors. In this work, we explore the prospects of such searches by implementing in our analysis an upper distance limit based on the sky-localization capabilities of the GW detectors from which meaningful triggers can be collected. We find that if each GW burst is associated with a total isotropic-equivalent energy of $\sim 10^{50} - 10^{51}$ erg emitted in UHE neutrinos, along with a corresponding beaming fraction of $1$%, GRAND and IceCube-Gen2 Radio have a large probability ($\sim 99$%) to detect a coincident neutrino event using the joint combination of CE+ET in a timescale of less than 15 years of operation for our fiducial choice of parameters. In case of nondetections, the parameter spaces can be constrained at $3σ$ level in similar timescales of operation. We also highlight and discuss the prospects of such joint radio neutrino detector network, their importance, and their role in facilitating synergic GW and neutrino observations in the next era of multimessenger astrophysics.

We show that if neutrinos are pseudo-Dirac, they can potentially affect the flavor ratio predictions for the high-energy astrophysical neutrino flux observed by IceCube. In this context, we point out a novel matter effect induced by the cosmic neutrino background (C$ν$B) on the flavor ratio composition. Specifically, the active-sterile neutrino oscillations over the astrophysical baseline lead to an energy-dependent flavor ratio at Earth due to the C$ν$B matter effect, which is in principle distinguishable from the vacuum oscillation effect, provided there is an asymmetry between the neutrino and antineutrino number densities, as well as a local C$ν$B overdensity. Considering the projected precision of the 3-neutrino oscillation parameter measurements and improved flavor triangle measurements, we show that the next-generation neutrino telescopes, such as KM3NeT and IceCube-Gen2, can in principle probe the pseudo-Dirac neutrino hypothesis and the C$ν$B matter effect.

Nuclear power reactors are the most intense man-made source of antineutrino's and have long been recognized as promising sources for coherent elastic neutrino-nucleus scattering (CE$ν$NS) studies. Its observation and the spectral shape of the associated recoil spectrum is sensitive to a variety of exotic new physics scenarios and many experimental efforts are underway. Within the context of the reactor antineutrino anomaly, which initially indicated eV-scale sterile neutrino's, the modeling of the reactor antineutrino spectrum has seen a significant evolution in the last decade. Even so, uncertainties remain due to a variety of nuclear structure effects, incomplete information in nuclear databases and fission dynamics complexities. Here, we investigate the effects of these uncertainties on one's ability to accurately distinguish new physics signals. For the scenarios discussed here, we find that reactor spectral uncertainties are similar in magnitude to the projected sensitivities pointing towards a need for $β$ spectroscopy measurements below the inverse $β$ decay threshold.

Scalar non-standard interactions (NSI) presents an exciting pathway for probing potential new physics that extends beyond the Standard Model (BSM). The scalar coupling of neutrinos with matter can appear as a sub-dominant effect that can impact the neutrino oscillation probabilities. The uniqueness of these interactions is that it can directly affect the neutrino mass matrix. This makes oscillations sensitive to the absolute neutrino mass. The effects of scalar NSI scales linearly with matter density which motivates its exploration in long-baseline sector. The presence of scalar NSI can influence the key measurements in the field of neutrino physics, including the precise determination of the leptonic CP phase ($δ_{CP}$), neutrino mass ordering and the octant of $θ_{23}$. The precise determination of $δ_{CP}$ is one of the major goals of DUNE, which is an upcoming long-baseline experiment. A better understanding of the impact of scalar NSI on CP measurement sensitivities is crucial for accurate interpretation of $δ_{CP}$ phase. In this work, we have explored the impact of the complex off-diagonal scalar NSI elements $η_{αβ}$ and their associated phases $φ_{αβ}$ on the CP-measurement sensitivities at DUNE. We have explored the impact of the neutrino mass scale on these sensitivities. We look for constraining these off-diagonal elements for different neutrino mass scales. We also explore their correlation with $δ_{CP}$, investigating potential degeneracies that can arise due to additional phases. We also perform a correlation study among different scalar NSI elements. We show that the inclusion of the complex scalar NSI elements can significantly modify the CP phase measurements.

We report the first detection of coherent elastic neutrino-nucleus scattering (CEvNS) on natural germanium, measured at the Spallation Neutron Source at Oak Ridge National Laboratory. The Ge-Mini detector of the COHERENT collaboration employs large-mass, low-noise, high-purity germanium spectrometers, enabling excellent energy resolution, and an analysis threshold of 1.5 keV electron-equivalent ionization energy. We observe a on-beam excess of 20.6 +7.1 -6.3 counts with a total exposure of 10.22 GWhkg and we reject the no-CEvNS hypothesis with 3.9 sigma significance. The result agrees with the predicted standard model of particle physics signal rate within 2 sigma.

We investigate the implications of the constraints following from the precise knowledge of the total Earth mass, $M_\oplus$, and moment of inertia, $I_\oplus$, and from the requirement that Earth be in hydrostatic equilibrium (EHE), in the neutrino tomography studies of the Earth density structure. In order to estimate the sensitivity of a given neutrino detector to possible deviations of the inner core (IC), outer core (OC), core (IC + OC) and mantle Earth densities from those obtained using geophysical and seismological data and described by the preliminary reference Earth model (PREM), in the statistical analyses performed within the neutrino tomography studies one typically varies the density of each of these structures. These variations, however, must respect the $M_\oplus$, $I_\oplus$ and EHE constraints. Working with PREM average densities we derive the $M_\oplus$, $I_\oplus$ and EHE constraints on the possible density variations when one approximates the Earth density structure with i) three layers - mantle, outer core and inner core, and ii) four layers - upper mantle, lower mantle, outer core and inner core. We get drastically different results in the two cases.

The fact that neutrinos carry a non-vanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass bears important relevance from particle physics to cosmology. In this work, we report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium $β$-decay close to the kinematic endpoint. Based on the first five neutrino-mass measurement campaigns, we derive a best-fit value of $m_ν^{2} = {-0.14^{+0.13}_{-0.15}}~\mathrm{eV^2}$, resulting in an upper limit of $m_ν< {0.45}~\mathrm{eV}$ at 90 % confidence level. With six times the statistics of previous data sets, amounting to 36 million electrons collected in 259 measurement days, a substantial reduction of the background level and improved systematic uncertainties, this result tightens KATRIN's previous bound by a factor of almost two.

Flux spectrum, event rate, and experimental sensitivity are investigated for the diffuse supernova neutrino background (DSNB), which originates from past stellar collapses and is also known as a supernova relic neutrino background. For this purpose, the contribution of collapses that lead to successful supernova (SN) explosion and black hole (BH) formation simultaneously, which are suggested to be a non-negligible population from the perspective of Galactic chemical evolution, is taken into account. If the BH-forming SNe involve the matter fallback onto the protoneutron star for the long term, their total emitted neutrino energy becomes much larger than that of ordinary SNe and failed SNe (BH formation without explosion). Then, in the case of the normal mass hierarchy in neutrino oscillations and with half of all core-collapse SNe being BH-forming SNe, the expected event rate according to the current DSNB model is enhanced by up to a factor of two due to the BH-forming SNe. While substantial uncertainties exist regarding the duration of the matter fallback, which determines the total amount of emitted neutrinos, and the fraction of BH-forming SNe, the operation time required to detect the DSNB at Hyper-Kamiokande would be reduced by such contribution in any case.

Black hole (BH) superradiance can provide strong constraints on the properties of ultralight bosons (ULBs). While most of the previous work has focused on the theoretical predictions, here we investigate the most suitable statistical framework to constrain ULB masses and self-interactions using BH spin measurements. We argue that a Bayesian approach based on a simple timescales analysis provides a clear statistical interpretation, deals with limitations regarding the reproducibility of existing BH analyses, incorporates the full information from BH data, and allows us to include additional nuisance parameters or to perform hierarchical modelling with BH populations in the future. We demonstrate the feasibility of our approach using mass and spin posterior samples for the X-ray binary BH M33 X-7 and, for the first time in this context, the supermassive BH IRAS 09149-6206. We explain the differences to existing ULB constraints in the literature and illustrate the effects of various assumptions about the superradiance process (equilibrium regime vs cloud collapse, higher occupation levels). As a result, our procedure yields the most statistically rigorous ULB constraints available in the literature, with important implications for the QCD axion and axion-like particles. We encourage all groups analysing BH data to publish likelihood functions or posterior samples as supplementary material to facilitate this type of analysis, and for theory developments to compress their findings to effective timescale modifications.

Long-standing anomalous experimental results from short-baseline neutrino experiments have persisted for decades. These results, when interpreted with one or more light sterile neutrinos, are inconsistent with numerous null results experimentally. However, if the sterile neutrino decays en route to the detector, this can mimic $ν_μ\to ν_e$ oscillation signals while avoiding many of these external constraints. We revisit this solution to the MiniBooNE and LSND puzzles in view of new data from the MicroBooNE experiment at Fermilab. Using MicroBooNE's liquid-argon time-projection chamber search for an excess of $ν_e$ in the Booster beam, we derive new limits in two models' parameter spaces of interest: where the sterile neutrino decays (I) via mixing with the active neutrinos, or (II) via higher-dimensional operators. We also provide an updated, comprehensive fit to the MiniBooNE neutrino- and antineutrino-beam data, including appearance ($ν_e$) and disappearance ($ν_μ$) channels. Despite alleviating the tension with muon neutrino disappearance experiments, we find that the latest MicroBooNE analysis rules out the decaying sterile neutrino solution in a large portion of the parameter space at more than $99\%$ CL.

Ultralight dark matter interacting with sterile neutrinos would modify the evolution and properties of the cosmic neutrino background through active-sterile neutrino mixing. We investigate how such an interaction would induce a redshift dependence in neutrino masses. We highlight that cosmological constraints on the sum of neutrino masses would require reinterpretation due to the effective mass generated by neutrino-dark matter interactions. Furthermore, we present an example where such interactions can alter the mass ordering of neutrinos in the early Universe, compared to what we expect today. We also address the expected changes in the event rates in a PTOLEMY-like experiment, which aims to detect the cosmic neutrino background via neutrino capture, and discuss projected constraints.

We present the first complete calculation of the Jarlskog invariant, a working measure of the strength of CP violation in the flavor oscillations of three light neutrino species, with the help of a full Euler-like block parametrization of the flavor structure in the canonical seesaw mechanism. We find that this invariant depends on 240 linear combinations of the 6 original phase parameters that are responsible for CP violation in the decays of three heavy Majorana neutrinos in 27 linear combinations as a whole, and thus provides the first model-independent connection between the microscopic and macroscopic matter-antimatter asymmetries.

The astrophysical origins of the majority of the IceCube neutrinos remain unknown. Effectively characterizing the spatial distribution of the neutrino samples and associating the events with astrophysical source catalogs can be challenging given the large atmospheric neutrino background and underlying non-Gaussian spatial features in the neutrino and source samples. In this paper, we investigate a framework for identifying and statistically evaluating the cross-correlations between IceCube data and an astrophysical source catalog based on the $k$-nearest-neighbor cumulative distribution functions ($k$NN-CDFs). We propose a maximum likelihood estimation procedure for inferring the true proportions of astrophysical neutrinos in the point-source data. We conduct a statistical power analysis of an associated likelihood ratio test with estimations of its sensitivity and discovery potential with synthetic neutrino data samples and a WISE-2MASS galaxy sample. We apply the method to IceCube's public ten-year point-source data and find no statistically significant evidence for spatial cross-correlations with the selected galaxy sample. We discuss possible extensions to the current method and explore the method's potential to identify the cross-correlation signals in data sets with different sample sizes.

In the mixed dark matter scenarios consisting of primordial black holes (PBHs) and particle dark matter (DM), PBHs can accrete surrounding DM particles to form ultracompact minihalos (UCMHs or clothed PBHs) even at an early epoch of the Universe. The distribution of DM particles in a UCMH follows a steeper density profile compared with a classical DM halo. It is expected that the DM annihilation rate is very large in UCMHs, resulting in a contribution to, e.g., the extragalactic neutrino flux. In this work, we investigate the extragalactic neutrino flux from clothed PBHs due to DM annihilation, and then the muon flux for neutrino detection. Compared with the atmospheric neutrino flux, we derive the upper limits on the cosmological abundance of PBHs for 10 years of exposure time of, e.g., the IceCube experiment. Compared with other constraints, although the upper limits obtained by us are not the strongest, it is a different way to study the cosmological abundance of PBHs.

Sixty years after the experimental discovery of CP violation in the quark sector, the existence of a similar CP violation in the lepton sector is still to be established. Actually, the structure of such a violation depends crucially on the origin of the neutrino masses. In an attempt at categorizing the leptonic sources of CP violation, we studied the $ν$SM, the Standard Model extended with three generations of sterile neutrinos, that can interpolate continuously between the Dirac and Majorana scenarios of neutrino masses. In particular, we perform a classification of the Jarlskog-like flavor invariants entering CP-violating observables and we study their suppression with the heavy Majorana mass in the seesaw limit of the model. To simplify the construction of the invariants, we introduce a graph-based method. With the guidance of the Hilbert series and plethystic logarithm of the theory, we construct the \emph{generating} and \emph{primary} sets of invariants for the $ν$SM for the first time. Unlike in the Standard Model and some other theories, we find that the numbers of generating invariants and the syzygies among them cannot immediately be read off from the plethystic logarithm, but require a more careful examination. Our analysis reveals that the \emph{generating} set contains 459 invariants, out of which 208 are CP-even and 251 are CP-odd. In the seesaw limit of the $ν$SM, we show that all parameters of the UV theory can be captured in the effective theory with a certain suppression with the heavy Majorana mass, while these parameters can only appear in a \emph{flavor-invariant} way with a \emph{higher} mass suppression. Furthermore, we discuss how the necessary and sufficient conditions for CP violation can be captured by utilizing these invariants. Along the way, we present useful algorithms to enumerate and build the flavor invariants.

Energetic cosmic rays scatter off the cosmic neutrino background throughout the history of the Universe, yielding a diffuse flux of cosmic relic neutrinos boosted to high energies. We calculate this flux under different assumptions of the cosmic-ray flux spectral slope and redshift evolution. The non-observation of the diffuse flux of boosted relic neutrinos with current high-energy neutrino experiments already excludes an average cosmic neutrino background overdensity larger than $\sim 10^{4}$ over cosmological distances. We discuss the future detectability of the diffuse flux of boosted relic neutrinos in light of neutrino overdensity estimates and cosmogenic neutrino backgrounds.

Since neutrinos have mass differences, they could decay into one another. But their lifetimes are likely long, even when shortened by new physics, so decay likely impacts neutrinos only during long trips. This makes high-energy astrophysical neutrinos, traveling for up to billions of light-years, sensitive probes of decay. However, their sensitivity must be tempered by reality. We derive from them thorough bounds on the neutrino lifetimes accounting for critical astrophysical unknowns and the nuances of neutrino detection. Using the diffuse neutrino flux, we disfavor lifetimes $τ\lesssim 20$-450 s $(m/{\rm eV})$, based on present IceCube data, and forecast factor-of-10 improvements by upcoming detectors. Using, for the first time, neutrinos from the active galaxy NGC 1068, extant unknowns preclude placing lifetime bounds today, but upcoming detectors could disfavor $τ\sim 100$-5000 s $(m/{\rm eV})$.

Neutrinos produced in the atmosphere traverse a column density of air before being detected at neutrino observatories like IceCube or KM3NeT. In this work, we extend the neutrino flavor evolution in the {nuSQuIDS} code accounting for the varying height of neutrino production and the variable air density in the atmosphere. These effects can lead to sizeable spectral distortions in standard neutrino oscillations and are crucial to accurately describe some new physics scenarios. As an example, we study a model of quasi-sterile neutrinos that induce resonant flavor conversions at neutrino energies of ${O}(300)\text{ MeV}$ in matter densities of $1 \text{ g/cm}^3$. In atmospheric air densities, the same resonance is then realized at neutrino energies of ${O}(300- 700)$~GeV. We find that the new resonance can deplete the $ν_μ+ \overlineν_μ$ flux at the IceCube Neutrino Observatory by as much as $10\%$ in the direction of the horizon.

The neutrino sector of the standard model of particles can contain more than one sterile neutrino states. Generally, existence of more sterile states leads to better, or at least equally good, fit to the short baseline anomalous data due to the larger number of parameters and interferences which create features in the oscillation pattern. However, for experiments like IceCube, where the sterile states distort the oscillation pattern of high energy atmospheric neutrinos through parametric and MSW resonances, addition of more sterile states leads to a more intense effect. Although the limits on one additional sterile neutrino state by IceCube data have been studied in the literature, bounds on the models with more sterile states are lacking. We analyze the one-year data set of atmospheric neutrinos collected by IceCube during the 2011-2012 and derive the limits on the parameter space of (3+2) scenario with two sterile neutrino states, taking into account the relevant systematic and statistical uncertainties and atmospheric neutrino flux variants. To facilitate the joint analysis of IceCube and short baseline data, we provide the table of $χ^2$ values from IceCube's data analysis as function of the parameters.

For the first time, we comprehensively examine the potential of a neutral-current interaction of reactor neutrino with $^{13}$C emitting a 3.685 MeV photon to identify the origin of the 5 MeV bump in reactor antineutrino spectra observed through the inverse beta decay (IBD) process. This anomaly may be due to new physics, reactor antineutrino flux inaccuracies, or IBD systematics. The 3.685 MeV photon released during the de-excitation of $^{13}$C$^\ast$ to its ground state is observable in liquid scintillator detectors. Remarkably, we confirm the powerfulness of our proposal by completely ruling out a new physics scenario explaining the bump from the existing NEOS data. We also explore the potential of current and forthcoming experiments, including solar neutrino studies at JUNO, pion and muon decay-at-rest experiments at OscSNS, and isotope decay-at-rest studies at Yemilab, to measure the cross-section precisely enough to distinguish the expected bump and the theoretical flux models via our channel. Additionally, we propose a novel method to track the time evolution of reactor isotopes by analyzing the $^{13}$C signal, which yields critical insights into the contributions of $^{235}$U and $^{239}$Pu to the bump, acting as a robust tool.

Gravitational waves (GWs) can alter the neutrino propagation distance and thus affect neutrino oscillations. This can result in a complete disappearance of the oscillatory behavior that competes with other sources of neutrino decoherence. We develop a set of criteria that determines under which conditions neutrino oscillations are sensitive to this effect. We find that current or near future neutrino oscillation experiments are not sufficiently sensitive to coherent GW signals but may probe the stochastic gravitational wave background if the energy resolution improves drastically by several orders of magnitude.

Neutrino oscillation experiments will be entering the precision era in the next decade with the advent of high statistics experiments like DUNE, HK, and JUNO. Correctly estimating the confidence intervals from data for the oscillation parameters requires very large Monte Carlo data sets involving calculating the oscillation probabilities in matter many, many times. In this paper, we leverage past work to present a new, fast, precise technique for calculating neutrino oscillation probabilities in matter optimized for long-baseline neutrino oscillations in the Earth's crust including both accelerator and reactor experiments. For ease of use by theorists and experimentalists, we provide fast c++ and fortran codes.

The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, $\sum m_ν< 70$ meV (95%). In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at $\sum m_ν= 0$ and is close to excluding even the minumum sum, 58 meV at 2$σ$. In this paper, we explore the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe. Allowing the clustering to be enhanced, we extended the DESI analysis to $\sum m_ν< 0$ and find $\sum m_ν= - 160 \pm 90$ meV (68%), and that the suppression of power from the minimum sum of neutrino masses is excluded at 99% confidence. We show this preference for negative masses makes it challenging to explain the result by a shift of cosmic parameters, such as the optical depth or matter density. We then show how a result of $\sum m_ν=0$ could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics that is accessible in a wide range of experiments. In addition, we discuss how an apparent signal with $\sum m_ν< 0$ can arise from new long range forces in the dark sector or from a primordial trispectrum that resembles the signal of CMB lensing.

We investigate how recent updates to neutrino oscillation parameters and the sum of neutrino masses influence the sensitivity of neutrinoless double-beta (0$νββ$) decay experiments. Incorporating the latest cosmological constraints on the sum of neutrino masses and laboratory measurements on oscillations, we determine the sum of neutrino masses for both the normal hierarchy (NH) and the inverted hierarchy (IH). Our analysis reveals a narrow range for the sum of neutrino masses, approximately 0.06 eV/c$^2$ for NH and 0.102 eV/c$^2$ for IH. Utilizing these constraints, we calculate the effective Majorana masses for both NH and IH scenarios, establishing the corresponding allowed regions. Importantly, we find that the minimum neutrino mass is non-zero, as constrained by the current oscillation parameters. Additionally, we estimate the half-life of 0$νββ$ decay using these effective Majorana masses for both NH and IH. Our results suggest that upcoming ton-scale experiments will comprehensively explore the IH scenario, while 100-ton-scale experiments will effectively probe the parameter space for the NH scenario, provided the background index can achieve 1 event/kton-year in the region of interest.

The origin of neutrino masses remains unknown. Both the vacuum mass and the dark mass generated by the neutrino interaction with dark matter (DM) particles or fields can fit the current oscillation data. The dark mass squared is proportional to the DM number density and therefore varies on the galactic scale with much larger values around the Galactic Center. This affects the group velocity and the arrival time delay of core-collapse supernovae (SN) neutrinos. This time delay, especially for the $ν_e$ neutronization peak with a sharp time structure, can be used to distinguish the vacuum and dark neutrino masses. For illustration, we explore the potential of DUNE which is sensitive to $ν_e$. Our simulations show that DUNE can distinguish the two neutrino mass origins at more than $5σ\,$C.L., depending on the observed local value of neutrino mass, the neutrino mass ordering, the DM density profile, and the SN location.

We revisit a method for determining the neutrino mass ordering by using precision measurements of the atmospheric $Δm^2$'s in both electron neutrino and muon neutrino disappearance channels, proposed by the authors in 2005 (hep-ph/0503283). The mass ordering is a very important outstanding question for our understanding of the elusive neutrino and determination of the mass ordering has consequences for other neutrino experiments. The JUNO reactor experiment will start data taking this year, and the precision of the atmospheric $Δm^2$'s from electron anti-neutrino measurements will improve by a factor of three from Daya Bay's 2.4 % to 0.8 % within a year. This measurement, when combined with the atmospheric $Δm^2$'s measurements from T2K and NOvA for muon neutrino disappearance, will contribute substantially to the $Δχ^2$ between the two remaining neutrino mass orderings. In this paper we derive a mass ordering sum rule that can be used to address the possibility that JUNO's atmospheric $Δm^2$'s measurement, when combined with other experiments in particular T2K and NOvA, can determine the neutrino mass ordering at the 3 $σ$ confidence level within one year of operation. For a confidence level of 5 $σ$ in a single experiment we will have to wait until the middle of the next decade when the DUNE experiment is operating.

Understanding the physics of the deep solar interior, and the more exotic environs of core-collapse supernovae (CCSN) and binary neutron-star (NS) mergers, is of keen interest in many avenues of research. To date, this physics is based largely on simulations via forward integration. While these simulations provide valuable constraints, it could be insightful to adopt the "inverse approach" as a point of comparison. Within this paradigm, parameters of the solar interior are not output based on an assumed model, but rather are inferred based on real data. We take the specific case of solar electron number density, which historically is taken as output from the standard solar model. We show how one may arrive at an independent constraint on that density profile based on available neutrino flavor data from the Earth-based Borexino experiment. The inference technique's ability to offer a unique lens on physics can be extended to other datasets, and to analogous questions for CCSN and NS mergers, albeit with simulated data.

Upcoming neutrino experiments will soon search for new neutrino interactions more thoroughly than ever before, boosting the prospects of extending the Standard Model. In anticipation of this, we forecast the capability of two of the leading long-baseline neutrino oscillation experiments, DUNE and T2HK, to look for new flavor-dependent neutrino interactions with electrons, protons, and neutrons that could affect the transitions between different flavors. We interpret their sensitivity in the context of long-range neutrino interactions, mediated by a new neutral boson lighter than $10^{-10}$ eV, and sourced by the vast amount of nearby and distant matter in the Earth, Moon, Sun, Milky Way, and beyond. For the first time, we explore the sensitivity of DUNE and T2HK to a wide variety of $U(1)^\prime$ symmetries, built from combinations of lepton and baryon numbers, each of which induces new interactions that affect oscillations differently. We find ample sensitivity: in all cases, DUNE and T2HK may constrain the existence of the new interaction even if it is supremely feeble, may discover it, and, in some cases, may identify the symmetry responsible for it.

We use recent evidence of TeV neutrino events from the most significant astrophysical sources detected by IceCube -- NGC 1068, TXS 0506+056, PKS 1424+240 -- to constrain the local and global overdensity of relic neutrinos and to explore potential new neutrino self-interactions. Assuming a relic neutrino overdensity, such high-energy neutrinos have travelled considerable distances through a sea of relic neutrinos and could have undergone scattering, altering their observed flux on Earth. Considering only Standard Model interactions, we constrain the relic overdensity to $η\leq 2 \times 10^{14}$ at the 90$\%$ confidence level, assuming the sum of neutrino masses saturates the cosmological bound, $\sum_i m_i = 0.13$ eV. We demonstrate that this limit improves for larger neutrino masses and study how it depends on the scale of the overdensity region. Considering new interactions between TeV-scale neutrinos and relic neutrinos, mediated by a light boson, we probe couplings of approximately $g \sim 10^{-2}$ with current data for a boson mass around the MeV scale. We demonstrate that this limit improves with larger neutrino masses and the scale of the overdensity region.

Neutrino propagation in the Galactic and extragalactic magnetic fields is considered. We extend an approach developed in \cite{Popov:2019nkr} to describe neutrino flavour and spin oscillations using wave packets. The evolution equations for the neutrino wave packets in a uniform and non-uniform magnetic fields are derived. The analytical expressions for neutrino flavour and spin oscillations probabilities accounting for damping due to the wave packet separation are obtained for the case of a uniform magnetic field. It is shown that terms in the flavour oscillations probabilities that depend on the magnetic field strength are characterized by two coherence lengths. One of the coherence lengths coincides with the coherence length for neutrino oscillations in vacuum, while the second one is proportional to the cube of the average neutrino momentum $p_0^3$. The probabilities of flavour and spin oscillations are calculated numerically for neutrino interacting with the non-uniform Galactic magnetic field. It is shown that oscillations on certain frequencies are suppressed on the Galactic scale due to the neutrino wave packets separation. The flavour compositions of high-energy neutrino flux coming from the Galactic centre and ultra-high energy neutrinos from an extragalactic sourse are calculated accounting for neutrino interaction with the magnetic field and decoherence due to the wave packet separation. It is shown that for neutrino magnetic moments $\sim 10^{-13} μ_B$ and larger these flavour compositions significantly differ from ones predicted by the vacuum neutrino oscillations scenario.

We explore the possibility of redshift-dependent deviations in the contribution of relativistic degrees of freedom to the radiation budget of the cosmos, conventionally parameterized by the effective number of neutrinos $N_{\rm eff}$, from the predictions of the standard model. We expand the deviations $ΔN_{\rm eff}(z)$ in terms of top-hat functions and treat their amplitudes as the free parameters of the theory to be measured alongside the standard cosmological parameters by the Planck measurements of the cosmic microwave background (CMB) anisotropies and Baryonic Acoustic Oscillations, as well as performing forecasts for futuristic CMB surveys such as PICO and CMB-S4. We reconstruct the history of $ΔN_{\rm eff}$ and find that with the current data the history is consistent with the standard scenario. Inclusion of the new degrees of freedom in the analysis increases $H_0$ to $68.71\pm 0.44$, slightly reducing the Hubble tension. With the smaller forecasted errors on the $ΔN_{\rm eff}(z)$ parametrization modes from future CMB surveys, very accurate bounds are expected within the possible range of dark radiation models.

In the ongoing vibrant experimental quest to assess whether the numerous indications for a light sterile neutrino are only experimental fluctuations or the manifestations of a profound and real underlying effect, one aspect which has recently attracted a specific interest is the statistical treatment of the data. Especially in cases of supposed positive hints, the correct statistical assessment of their significance is of paramount importance, to avoid that potential overstatements lead to a wrong understanding of the real status of the experimental investigation in the field. In this work I show how latest crucial advancements in the statistical data processing for the interpretation of the output of a sterile search can be effectively put and understood in the context of the Look Elsewhere Effect phenomenon, developed and now of routine usage for results interpretation in other areas of HEP research.

Neutrino telescopes, including IceCube, can detect galactic supernova events by observing the collective rise in photomultiplier count rates with a sub-second time resolution. Leveraging precise timing, we demonstrate the ability of neutrino telescopes to explore new weakly coupled states emitted from supernovae and subsequently decaying to neutrinos. Our approach utilizes publicly available packages, \texttt{ASTERIA} and \texttt{SNEWPY}, for simulating detector responses and parametrizing neutrino fluxes originating from Standard Model and new physics. We present results for two beyond the Standard Model scenarios and introduce the tool developed for testing a diverse range of new physics models.

We report on a measurement of astrophysical tau neutrinos with 9.7 years of IceCube data. Using convolutional neural networks trained on images derived from simulated events, seven candidate $ν_τ$ events were found with visible energies ranging from roughly 20 TeV to 1 PeV and a median expected parent $ν_τ$ energy of about 200 TeV. Considering backgrounds from astrophysical and atmospheric neutrinos, and muons from $π^\pm/K^\pm$ decays in atmospheric air showers, we obtain a total estimated background of about 0.5 events, dominated by non-$ν_τ$ astrophysical neutrinos. Thus, we rule out the absence of astrophysical $ν_τ$ at the $5σ$ level. The measured astrophysical $ν_τ$ flux is consistent with expectations based on previously published IceCube astrophysical neutrino flux measurements and neutrino oscillations.

Taking the tri-bimaximal flavor mixing pattern as a particular basis, we propose a new way to expand the $3\times 3$ unitary Pontecorvo-Maki-Nakagawa-Sakata (PMNS) lepton flavor mixing matrix $U$ in powers of the magnitude of its smallest element $ξ\equiv \left|U^{}_{e 3}\right| \simeq 0.149$. Such a Wolfenstein-like parametrization of $U$ allows us to easily describe the salient features and fine structures of flavor mixing and CP violation, both in vacuum and in matter.

We study the prospects for measuring the time variation of solar and atmospheric neutrino fluxes at future large-scale Xenon and Argon dark matter detectors. For solar neutrinos, a yearly time variation arises from the eccentricity of the Earth's orbit, and, for charged current interactions, from a smaller energy-dependent day-night variation to due flavor regeneration as neutrinos travel through the Earth. For a 100-ton Xenon detector running for 10 years with a Xenon-136 fraction of $\lesssim 0.1\%$, in the electron recoil channel a time-variation amplitude of about 0.8\% is detectable with a power of 90\% and the level of significance of 10\%. This is sufficient to detect time variation due to eccentricity, which has amplitude of $\sim 3\%$. In the nuclear recoil channel, the detectable amplitude is about 10\% under current detector resolution and efficiency conditions, and this generally reduces to about 1\% for improved detector resolution and efficiency, the latter of which is sufficient to detect time variation due to eccentricity. Our analysis assumes both known and unknown periods. We provide scalings to determine the sensitivity to an arbitrary time-varying amplitude as a function of detector parameters. Identifying the time variation of the neutrino fluxes will be important for distinguishing neutrinos from dark matter signals and other detector-related backgrounds, and extracting properties of neutrinos that can be uniquely studied in dark matter experiments.

A measurement of the diffuse astrophysical neutrino spectrum is presented using IceCube data collected from 2011-2022 (10.3 years). We developed novel detection techniques to search for events with a contained vertex and exiting track induced by muon neutrinos undergoing a charged-current interaction. Searching for these starting track events allows us to not only more effectively reject atmospheric muons but also atmospheric neutrino backgrounds in the southern sky, opening a new window to the sub-100 TeV astrophysical neutrino sky. The event selection is constructed using a dynamic starting track veto and machine learning algorithms. We use this data to measure the astrophysical diffuse flux as a single power law flux (SPL) with a best-fit spectral index of $γ= 2.58 ^{+0.10}_{-0.09}$ and per-flavor normalization of $φ^{\mathrm{Astro}}_{\mathrm{per-flavor}} = 1.68 ^{+0.19}_{-0.22} \times 10^{-18} \times \mathrm{GeV}^{-1} \mathrm{cm}^{-2} \mathrm{s}^{-1} \mathrm{sr}^{-1}$ (at 100 TeV). The sensitive energy range for this dataset is 3 - 550 TeV under the SPL assumption. This data was also used to measure the flux under a broken power law, however we did not find any evidence of a low energy cutoff.

We investigate the potential impact of neutrino quantum decoherence on the precision measurements of standard neutrino oscillation parameters in the DUNE and T2HK experiments. We show that the measurement of $δ_\text{CP}$, $\sin^2θ_{13}$ and $\sin^2θ_{23}$ is stronger effected in DUNE than in T2HK. On the other hand, DUNE would have a better sensitivity than T2HK to observe decoherence effects. By performing a combined analysis of DUNE and T2HK we show that a robust measurement of standard parameters would be possible, which is not guaranteed with DUNE data alone.

New physics contributions to the (anti)neutrino-nucleon elastic scattering process can be constrained by precision measurements, with controlled Standard Model uncertainties. In a large class of new physics models, interactions involving charged leptons of different flavor can be related, and the large muon flavor component of accelerator neutrino beams can mitigate the lepton mass suppression that occurs in other low-energy measurements. We employ the recent high-statistics measurement of the cross section for $\barν_μp \to μ^+ n$ scattering on the hydrogen atom by MINERvA to place new confidence intervals on tensor and scalar neutrino-nucleon interactions: $\mathfrak{Re} C_T = -1^{+14}_{-13} \times 10^{-4}$, $|\mathfrak{Im} C_T| \le 1.3 \times 10^{-3}$, and $|\mathfrak{Im} C_S| = 45^{+13}_{-19} \times 10^{-3}$. These results represent a reduction in uncertainty by a factor of $2.1$, $3.1$, and $1.2$, respectively, compared to existing constraints from precision beta decay.

The Forward Search Experiment (FASER) at CERN's Large Hadron Collider (LHC) has recently directly detected the first collider neutrinos. Neutrinos play an important role in all FASER analyses, either as signal or background, and it is therefore essential to understand the neutrino event rates. In this study, we update previous simulations and present prescriptions for theoretical predictions of neutrino fluxes and cross sections, together with their associated uncertainties. With these results, we discuss the potential for possible measurements that could be carried out in the coming years with the FASER neutrino data to be collected in LHC Run 3 and Run 4.

In this letter, we study the potential of boosting the atmospheric neutrino experiments sensitivity to the neutrino mass ordering (NMO) sensitivity by incorporating inelasticity measurements. We show how this observable improves the sensitivity to the NMO and the precision of other neutrino oscillation parameters relevant to atmospheric neutrinos, specifically in the IceCube-Upgrade and KM3NeT-ORCA detectors. Our results indicate that an oscillation analysis of atmospheric neutrinos including inelasticity information has the potential to enhance the ordering discrimination by several units of $χ^2$ in the assumed scenario of 5 and 3 years of running of IceCube-Upgrade and KM3NeT-ORCA detectors, respectively.

We address the consequence of invisible neutrino decay within the framework of two long base-line neutrino experiments: T2HKK (Tokai-to-Hyper-Kamiokande-to-Korea) and DUNE (Deep Underground Neutrino experiment). Our primary objective is to bring out the aspects of CC (charged current) and NC (neutral current) measurements at DUNE in the context of invisible neutrino decay. We find that the inclusion of NC measurements with the CC measurements enhances its ability to constrain invisible neutrino decay. Further, the synergy between DUNE and T2HKK improves the constraints on invisible neutrino decay. At 3$σ$ C.L. (confidence level) the derived constraint is $τ_{3}/m_{3}\geq6.21\times10^{-11}$ s/eV. Additionally, if nature prefers $ν_{3}$ to be unstable and the decay width is $τ_{3}/m_{3}= 2.2\times10^{-11}$ s/eV, this combination can exclude the no-decay scenario at more than 5$σ$ C.L. Although the CP sensitivity is not much hindered in the presence of invisible neutrino decay, the measurements of $θ_{23}$ and the ability to resolve octant of $θ_{23}$ is significantly influenced in these individual experiments. In the presence of invisible neutrino decay, the synergy between DUNE and T2HKK can exclude the wrong octant somewhat more effectively than either experiment alone.

We constrain the neutrino-dark matter cross section using properties of the dark matter density profiles of Milky Way dwarf spheroidal galaxies. The constraint arises from core-collapse supernova neutrinos scattering on dark matter as a form of energy injection, allowing the transformation of the dark matter density profile from a cusped profile to a flatter profile. We assume a standard cosmology of dark energy and cold, collisionless, and non-self-interacting dark matter. By requiring that the dark matter cores do not lose too much mass or overshoot constraints from stellar kinematics, we place an upper limit on the cross section of $σ_{ν-\mathrm{DM}}(E_ν=15 \, \mathrm{MeV}, m_χ\lesssim130 \, \mathrm{GeV}) \approx 3.4 \times 10^{-23} \, \mathrm{cm^2}$ and $σ_{ν-\mathrm{DM}}(E_ν=15 \, \mathrm{MeV}, m_χ\gtrsim130 \, \mathrm{GeV}) \approx 3.2 \times 10^{-27} \left( \frac{m_χ}{1\,\mathrm{GeV}}\right)^2\, \mathrm{cm^2}$, which is stronger than previous bounds for these energies. Consideration of baryonic feedback or host galaxy effects on the dark matter profile can strengthen this constraint.

In this study, we comprehensively characterized and optimized a cryogenic pure CsI (pCsI) detector. We utilized a {$\SI{2}{cm}\times\SI{2}{cm}\times\SI{2}{cm}$} cube crystal coupled with a HAMAMATSU R11065 photomultiplier tube, achieving a remarkable light yield of \SI{35.2}{PE/\keV_{ee}} and an unprecedented energy resolution of \SI{6.9}{\%} at {\SI{59.54}{\keV}}. Additionally, we measured the scintillation decay time of pCsI, which was significantly shorter than that of CsI(Na) at room temperature. Furthermore, we investigated the impact of temperature, surface treatment, and crystal shape on light yield. Notably, the light yield peaked at approximately \SI{20}{\K} and remained stable within the range of \SI{70}--\SI{100}{\K}. The light yield of the polished crystals was approximately 1.5 times greater than that of the ground crystals, whereas the crystal shape exhibited minimal influence on the light yield. These results are crucial for the design of the \SI{10}{\kg} pCsI detector for the future CLOVERS (Coherent eLastic neutrinO(V)-nucleus scattERing at China Spallation Neutron Source (CSNS)) experiment.`

Physical systems in real life are inextricably linked to their surroundings and never completely separated from them. Truly closed systems do not exist. The phenomenon of decoherence, which is brought about by the interaction with the environment, removes the relative phase of quantum states in superposition and makes them incoherent. In neutrino physics, decoherence, although extensively studied has only been analyzed thus far, exclusively in terms of its dissipative characteristics. While it is true that dissipation, or the exponential suppression, eventually is the main observable effect, the exchange of energy between the medium and the system, is an important factor that has been overlooked up until now. In this work, we introduce this term and analyze its consequences.

BSM electromagnetic properties of neutrinos may lead to copious production of sterile neutrinos in the hot and dense core of a core-collapse supernova. In this work, we focus on the active-sterile transition magnetic moment portal for heavy sterile neutrinos. Firstly, we revisit the SN1987A cooling bounds for dipole portal using the integrated luminosity method, which yields more reliable results (especially in the trapping regime) compared to the previously explored via emissivity loss, aka the Raffelt criterion. Secondly, we obtain strong bounds on the dipole coupling strength reaching as low as $10^{-11} \text{ GeV}^{-1}$ from energy deposition, i.e., constrained from the observation of explosion energies of underluminous Type IIP supernovae. In addition, we find that sterile neutrino production from Primakoff upscattering off of proton dominates over scattering off of electron for low sterile neutrino masses.

Extragalactic and galactic cosmic rays scatter with the cosmic neutrino background during propagation to Earth, yielding a flux of relic neutrinos boosted to larger energies. If an overdensity of relic neutrinos is present in galaxies, and neutrinos are massive enough, this flux might be detectable by high-energy neutrino experiments. For a lightest neutrino of mass $m_ν \sim 0.1$ eV, we find an upper limit on the local relic neutrino overdensity of $\sim 10^{13}$ and an upper limit on the relic neutrino overdensity at TXS 0506+056 of $\sim 10^{10}$. Future experiments like GRAND or IceCube-Gen2 could improve these bounds by orders of magnitude.

We present the first experimental constraints on models with many additional neutrino species in an analysis of current neutrino data. These types of models are motivated as a solution to the hierarchy problem by lowering the species scale of gravity to TeV. Additionally, they offer a natural mechanism to generate small neutrino masses and provide interesting dark matter candidates. This study analyzes data from DayaBay, KamLAND, MINOS, NOvA and KATRIN. We do not find evidence for the presence of any additional neutrino species, therefore we report lower bounds on the allowed number of neutrino species realized in nature. For the normal/inverted neutrino mass ordering, we can give a lower bound on the number of neutrino species of O(30) and O(100), respectively, over a large range of the parameter space.

The large distances travelled by neutrinos emitted from the Sun and core-collapse supernovae together with the characteristic energy of such neutrinos provide ideal conditions to probe their lifetime, when the decay products evade detection. We investigate the prospects of probing invisible neutrino decay capitalising on the detection of solar and supernova neutrinos as well as the diffuse supernova neutrino background (DSNB) in the next-generation neutrino observatories Hyper-Kamiokande, DUNE, JUNO, DARWIN, and RES-NOVA. We find that future solar neutrino data will be sensitive to values of the lifetime-to-mass ratio $τ_1/m_1$ and $τ_2/m_2$ of $\mathcal{O}(10^{-1} - 10^{-2})$ s/eV. From a core-collapse supernova explosion at $10$ kpc, lifetime-to-mass ratios of the three mass eigenstates of $\mathcal{O}(10^5)$ s/eV could be tested. After $20$ years of data taking, the DSNB would extend the sensitivity reach of $τ_1/m_1$ to $10^{8}$ s/eV. These results promise an improvement of about $6 -15$ orders of magnitude on the values of the decay parameters with respect to existing limits.

Precision measurements of neutrino-electron scattering may provide a viable way to test the non-minimal form of the charged and neutral current weak interactions within a hypothetical near-detector setup for the Deep Underground Neutrino Experiment (DUNE). Although low-statistics, these processes are clean and provide information complementing the results derived from oscillation studies. They could shed light on the scale of neutrino mass generation in low-scale seesaw schemes.

We perform an updated analysis of long-baseline accelerator data in the framework of neutrino oscillations in presence of invisible neutrino decay. We analyze data from T2K, NOvA and MINOS/MINOS+ and show that the combined analysis of all experiments improves the previous bound from long-baseline data by approximately one order of magnitude.

We calculate the neutrino-electron elastic scattering cross section, extending the results previously obtained in arXiv:1702.05721v2, in the presence of generic new interactions that take into account all the effects caused by finite neutrino masses. We address the potential significance of a heavy neutrino sector during precision measurements, particularly for tau neutrinos scattering with masses in the MeV range, for which the existing upper bounds on $|U_{τ4}|^2$ would result in conceivably measurable contributions. Finally, we comment on the possibility to distinguish between Dirac and Majorana neutrinos, including the analysis of the new emerging parameters and its application to illustrative model-dependent scenarios.

The behavior of neutrinos is the only phenomenon that cannot be explained by the standard model of particle physics. Because of these mysterious neutrino interactions observed in nature, at present, there is growing interest in this field and ongoing or planned neutrino experiments are seeking solutions to this mystery very actively. The design of neutrino experiments and the analysis of neutrino data rely on precise computations of neutrino oscillations and scattering processes in general. Motivated by this, we developed a software package that calculates neutrino production and oscillation in nuclear reactors, neutrino-electron scattering of solar neutrinos, and the oscillation of neutrinos from radioactive isotopes for the search of sterile neutrinos. This software package is validated by reproducing the result of calculations and observations in other publications. We also demonstrate the feasibility of this package by calculating the sensitivity of a liquid scintillator detector, currently in planning, to the sterile neutrinos. This work is expected to be used in designs of future neutrino experiments.

The BOREXINO experiment has been collecting solar neutrino data since 2007, providing the opportunity to study the variation of the event rate over a decade. We find that at 96 \% C.L., the rate of low energy events shows a time modulation favoring a correlation with a flux from Jupiter. We present a new physics model, the Jovian Whisper Model, based on dark matter of mass $\sim 0.1-4$ GeV captured by Jupiter that can account for such modulation. We discuss how the Jovian Whisper Model (JWM) can be tested.

In this work, the sensitivity of future germanium-based reactor neutrino experiments to the weak mixing angle $\sin^{2}θ_{W}$, and to the presence of new light vector bosons is investigated. By taking into account key experimental features with their uncertainties and the application of a data-driven and state-of-the-art reactor antineutrino spectrum, the impact of detection threshold and experimental exposure is assessed in detail for an experiment relying on germanium semiconductor detectors. With the established analysis framework, the precision on the Weinberg angle, and capability of probing the parameter space of a universally coupled mediator model, as well as a U(1)$_{\rm B-L}$-symmetric model are quantified. Our investigation finds the next-generation of germanium-based reactor neutrino experiments in good shape to determine the Weinberg angle $\sin^{2}θ_{W}$ with $<10$ % precision using the low-energetic neutrino channel of CE$ν$NS. In addition, the current limits on new light vector bosons determined by reactor experiments can be lowered by about an order of magnitude via the combination of both CE$ν$NS and E$ν$eS. Consequently, our findings provide strong phenomenological support for future experimental endeavours close to a reactor site.

Long-baseline neutrino oscillation experiments require external constraints on $\sin^2θ_{12}$ and $Δm_{21}^2$ to make precision measurements of the leptonic mixing matrix. These constraints come from measurements of the Mikheyev-Smirnov-Wolfenstein (MSW) mixing in solar neutrinos. Here we develop an MSW large mixing angle approximation in the presence of heavy neutral leptons which adds a single new parameter ($α_{11}$) representing the magnitude of the mixing between the $ν_e$ state and the heavy sector. We use data from the Borexino, SNO and KamLAND collaborations to find a solar constraint appropriate for heavy neutral lepton searches in long-baseline oscillation experiments. Solar data limits the magnitude of the non-unitary parameter to $(1-α_{11}) < 0.046$ at the $99\%$ credible interval and yields a strongly correlated constraint on the solar mass splitting and the magnitude of $ν_e$ non-unitary mixing.

Current long-baseline accelerator experiments, NOvA and T2K, are making excellent measurements of neutrino oscillations and the next generation of experiments, DUNE and HK, will make measurements at the $\mathcal O(1\%)$ level of precision. These measurements are a combination of the appearance channel which is more challenging experimentally but depends on many oscillation parameters, and the disappearance channel which is somewhat easier and allows for precision measurements of the atmospheric mass splitting and the atmospheric mixing angle. It is widely recognized that the matter effect plays a key role in the appearance probability, yet the effect on the disappearance probability is surprisingly small for these experiments. Here we investigate both exactly how small the effect is and show that it just begins to become relevant in the high statistics regime of DUNE.

The Conus experiment studies coherent elastic neutrino-nucleus scattering in four 1 kg germanium spectrometers. Low ionization energy thresholds of 210 eV were achieved. The detectors were operated inside an optimized shield at the Brokdorf nuclear power plant which provided a reactor antineutrino flux of up to 2.3$\cdot$10$^{13}$\,cm$^{-2}$s$^{-1}$. In the final phase of data collection at this site, the constraints on the neutrino interaction rate were improved by an order of magnitude as compared to the previous Conus analysis. The new limit of less than 0.34 signal events kg$^{-1}$\,d$^{-1}$ is within a factor 2 of the rate predicted by the standard model. This constraint is discussed in the context of conflicting measurements and results from another reactor neutrino experiment using similar technology.

It has been claimed that the coherent scattering of relic neutrinos with the Earth will result in a neutrino-antineutrino asymmetry of $\mathcal{O}(10^{-4})$ on the Earth surface, which is five orders of magnitude larger than the naive model expectation. In this work we show that this overdensity was overestimated for the perfectly round Earth by solving the exact solution with partial waves. The maximal asymmetry after summing over all the angular modes is only around $10^{-8}$ above the ground. To achieve the proposed asymmetry of $\mathcal{O}(10^{-4})$, a special geography may be needed as the experimental site.

The proton-proton ($pp$) fusion chain dominates the neutrino production from the Sun. The uncertainty of the predicted $pp$ neutrino flux is at the sub-percent level, whereas that of the best measurement is $\mathcal{O}(10\%)$. In this paper, we present the first result to measure the solar $pp$ neutrinos in the electron recoil energy range from 24 to 144 keV, using the PandaX-4T commissioning data with 0.63 tonne$\times$year exposure. The $pp$ neutrino flux is determined to be $(8.0 \pm 3.9 \,{\rm{(stat)}} \pm 10.0 \,{\rm{(syst)}} )\times 10^{10}\, $$\rm{s}^{-1} \rm{cm}^{-2}$, consistent with Standard Solar Model and existing measurements, corresponding to a flux upper limit of $23.3\times 10^{10}\, $$\rm{s}^{-1} \rm{cm}^{-2}$ at 90\% C.L..

The full data set of the Daya Bay reactor neutrino experiment is used to probe the effect of the charged current non-standard interactions (CC-NSI) on neutrino oscillation experiments. Two different approaches are applied and constraints on the corresponding CC-NSI parameters are obtained with the neutrino flux taken from the Huber-Mueller model with a $5\%$ uncertainty. For the quantum mechanics-based approach (QM-NSI), the constraints on the CC-NSI parameters $ε_{eα}$ and $ε_{eα}^{s}$ are extracted with and without the assumption that the effects of the new physics are the same in the production and detection processes, respectively. The approach based on the weak effective field theory (WEFT-NSI) deals with four types of CC-NSI represented by the parameters $[\varepsilon_{X}]_{eα}$. For both approaches, the results for the CC-NSI parameters are shown for cases with various fixed values of the CC-NSI and the Dirac CP-violating phases, and when they are allowed to vary freely. We find that constraints on the QM-NSI parameters $ε_{eα}$ and $ε_{eα}^{s}$ from the Daya Bay experiment alone can reach the order $\mathcal{O}(0.01)$ for the former and $\mathcal{O}(0.1)$ for the latter, while for WEFT-NSI parameters $[\varepsilon_{X}]_{eα}$, we obtain $\mathcal{O}(0.1)$ for both cases.

This paper explores core-collapse supernovae as crucial targets for neutrino telescopes, addressing uncertainties in their simulation results. We comprehensively analyze eighteen modern simulations and discriminate among supernova models using realistic detectors and interactions. A significant correlation between the total neutrino energy and cumulative counts, driven by massive lepton neutrinos and oscillations, is identified, particularly noticeable with the DUNE detector. Bayesian techniques indicate strong potential for model differentiation during a Galactic supernova event, with HK excelling in distinguishing models based on equation of state, progenitor mass, and mixing scheme.

We investigate the effect on neutrino oscillations generated by beyond-the-standard-model interactions between neutrinos and matter. Specifically, we focus on scalar-mediated non-standard interactions (NSI) whose impact fundamentally differs from that of vector-mediated NSI. Scalar NSI contribute as corrections to the neutrino mass matrix rather than the matter potential and thereby predict distinct phenomenology from the vector-mediated ones. Similar to vector-type NSI, the presence of scalar-mediated neutrino NSI can influence measurements of oscillation parameters in long-baseline neutrino oscillation experiments, with a notable impact on CP measurement in the case of DUNE. Our study focuses on the effect of scalar NSI on neutrino oscillations, using DUNE as an example. We introduce a model-independent parameterization procedure that enables the examination of the impact of all non-zero scalar NSI parameters simultaneously. Subsequently, we convert DUNE's sensitivity to the NSI parameters into projected sensitivity concerning the parameters of a light scalar model. We compare these results with existing non-oscillation probes. Our findings reveal that the region of the light scalar parameter space sensitive to DUNE is predominantly excluded by non-oscillation probes, except for scenarios with very light mediator mass.

We investigate new physics with light-neutral mediators through coherent elastic neutrino-nucleus scattering (CE$ν$NS) at low energies. These mediators, with a mass of less than $1$ GeV, are common properties for extensions of the Standard Model (SM). We consider general scalar, vector, and tensor interactions allowed by Lorentz invariance and involve universal light mediators accordingly. In addition, we study an additional vector gauge boson with an associated $U(1)'$ gauge group for a variety of models including $U(1)_{B-L}$, $U(1)_{B-3L_e}$, $U(1)_{B-3L_μ}$, and $U(1)_{B-3L_τ}$. These models differ in the fermion charges, which determine their contributions within the CE$ν$NS process. The effects of each model are investigated by embedding them in the SM process using solar neutrino flux. We derive new limits on the coupling-mass plane of these models from the latest CDEX-10 data. We also present projected sensitivities involving the future experimental developments for each model. Our results provide more stringent constraints in some regions, compared to previous works. Furthermore, the projected sensitivities yield an improvement of up to one order of magnitude.

We show that high-energy astrophysical neutrinos produced in the cores of heavily obscured active galactic nuclei (AGNs) can undergo strong matter effects, thus significantly influencing their source flavor ratios. In particular, matter effects can completely modify the standard interpretation of the flavor ratio measurements in terms of the physical processes occurring in the sources (e.g., $pp$ versus $pγ$, full pion-decay chain versus muon-damped pion decay). We contrast our results with the existing flavor ratio measurements at IceCube, as well as with projections for next-generation neutrino telescopes like IceCube-Gen2. Signatures of these matter effects in neutrino flavor composition would not only bring more evidence for neutrino production in central AGN regions, but would also be a powerful probe of heavily Compton-thick AGNs, which escape conventional observation in $X$-rays and other electromagnetic wavelengths.

We thoroughly explore the cosmic gravitational focusing of cosmic neutrino fluid (C$ν$F) by dark matter (DM) halo using both general relativity for a point source of gravitational potential and Boltzmann equations for continuous overdensities. Derived in the general way for both relativistic and non-relativistic neutrinos, our results show that the effect has fourth power dependence on the neutrino mass and temperature. With nonlinear mass dependence which is different from the cosmic microwave background (CMB) and large scale structure (LSS) observations, the cosmic gravitational focusing can provide an independent cosmological way of measuring the neutrino mass and ordering. We take DESI as an example to illustrate that the projected sensitivity as well as its synergy with existing terrestrial neutrino oscillation experiments and other cosmological observations can significantly improve the neutrino mass measurement.

From a cosmological perspective, scalar fields are well-motivated dark matter and dark energy candidates. Several possibilities of neutrino couplings with a time-varying cosmic field have been investigated in the literature. In this work, we present a framework in which violations of Lorentz invariance (LIV) and $CPT$ symmetry in the neutrino sector could arise from an interaction among neutrinos with a time-varying scalar field. Furthermore, some cosmological and phenomenological aspects and constraints concerning this type of interaction are discussed. Potential violations of Lorentz and $CPT$ symmetries at present and future neutrino oscillation experiments such as IceCube and KM3NeT can probe this scenario.

We investigate cosmological bounds on sterile neutrino masses in the light of the Hubble and $S_8$ tensions. We argue that non-zero masses for sterile neutrinos are inferred at 2$σ$ level in some extended models such as varying dark energy equation of state, when a direct measurement of the Hubble constant $H_0$ and weak lensing measurement of dark energy survey (DES) are taken into account. Furthermore, the Hubble and $S_8$ tensions are also reduced in such a framework. We also consider the case where a non-flat Universe is allowed and show that a slightly open Universe may be favored in models with sterile neutrinos in the context of the cosmological tensions.

In this paper, we study the connection between the tribimaximal and bitrimaximal mixing patterns. In doing so, we are forced to work in a non-diagonal charged lepton basis. This leads to several relations that must hold between the lepton mixing angles. After a short discussion, we analyze the underlying flavor symmetry responsible for this prediction. Finally, we add CP violation to bitrimaximal mixing and study its effect on the flavor symmetry group.

With just the Standard Model Higgs doublet, there are only three types of seesaw models that generate light Majorana neutrino masses at tree level after electroweak spontaneous symmetry breaking. However, if there exist additional TeV scalars acquiring vacuum expectation values, coupled with heavier fermionic multiplets, several new seesaw models become possible. These new seesaws are the primary focus of this study and correspond to the tree-level ultraviolet completions of the effective operators studied in a companion publication. We are interested in the genuine cases, in which the standard seesaw contributions are absent. In addition to the tree-level generation of neutrino masses, we also consider the one-loop contributions. Furthermore, we construct low-energy versions that exhibit a very rich phenomenology. Specifically, we scrutinise the generation of dimension-6 operators and explore their implications, including non-unitarity of the leptonic mixing matrix, non-universal $Z-$boson interactions, and lepton flavor violation. Finally, we provide (Generalised) Scotogenic-like variants that incorporate viable dark matter candidates.

Light hypothetical particles with masses up to $\mathcal{O}(100)\ {\rm MeV}$ can be produced in the core of supernovae. Their subsequent decays to neutrinos can produce a flux component with higher energies than the standard flux. We study the impact of heavy neutral leptons, $Z'$ bosons, in particular ${\rm U(1)}_{L_μ-L_τ}$ and ${\rm U(1)}_{B-L}$ gauge bosons, and majorons coupled to neutrinos flavor-dependently. We obtain new strong limits on these particles from no events of high-energy SN 1987A neutrinos and their future sensitivities from observations of galactic supernova neutrinos.

When a star undergoes core collapse, a vast amount of energy is released in a ~10 s long burst of neutrinos of all species. Inverse beta decay in the star's hydrogen envelope causes an electromagnetic cascade which ultimately results in a flare of gamma rays - an "echo" of the neutrino burst - at the characteristic energy of 0.511 MeV. We study the phenomenology and detectability of this flare. Its luminosity curve is characterized by a fast, seconds-long, rise and an equally fast decline, with a minute- or hour-long plateau in between. For a near-Earth star (distance D<1 kpc) the echo will be observable at near future gamma ray telescopes with an effective area of 10^3 cm^2 or larger. Its observation will inform us on the envelope size and composition. In conjunction with the direct detection of the neutrino burst, it will also give information on the neutrino emission away from the line of sight and will enable tests of neutrino propagation effects between the stellar surface and Earth.

An analysis of solar neutrino data from the fourth phase of Super-Kamiokande~(SK-IV) from October 2008 to May 2018 is performed and the results are presented. The observation time of the data set of SK-IV corresponds to $2970$~days and the total live time for all four phases is $5805$~days. For more precise solar neutrino measurements, several improvements are applied in this analysis: lowering the data acquisition threshold in May 2015, further reduction of the spallation background using neutron clustering events, precise energy reconstruction considering the time variation of the PMT gain. The observed number of solar neutrino events in $3.49$--$19.49$ MeV electron kinetic energy region during SK-IV is $65,443^{+390}_{-388}\,(\mathrm{stat.})\pm 925\,(\mathrm{syst.})$ events. Corresponding $\mathrm{^{8}B}$ solar neutrino flux is $(2.314 \pm 0.014\, \rm{(stat.)} \pm 0.040 \, \rm{(syst.)}) \times 10^{6}~\mathrm{cm^{-2}\,s^{-1}}$, assuming a pure electron-neutrino flavor component without neutrino oscillations. The flux combined with all SK phases up to SK-IV is $(2.336 \pm 0.011\, \rm{(stat.)} \pm 0.043 \, \rm{(syst.)}) \times 10^{6}~\mathrm{cm^{-2}\,s^{-1}}$. Based on the neutrino oscillation analysis from all solar experiments, including the SK $5805$~days data set, the best-fit neutrino oscillation parameters are $\rm{sin^{2} θ_{12,\,solar}} = 0.306 \pm 0.013 $ and $Δm^{2}_{21,\,\mathrm{solar}} = (6.10^{+ 0.95}_{-0.81}) \times 10^{-5}~\rm{eV}^{2}$, with a deviation of about 1.5$σ$ from the $Δm^{2}_{21}$ parameter obtained by KamLAND. The best-fit neutrino oscillation parameters obtained from all solar experiments and KamLAND are $\sin^{2} θ_{12,\,\mathrm{global}} = 0.307 \pm 0.012 $ and $Δm^{2}_{21,\,\mathrm{global}} = (7.50^{+ 0.19}_{-0.18}) \times 10^{-5}~\rm{eV}^{2}$.

The increasingly precise neutrino experiments raise the hope for searching for new physics through studying the impact of Neutral Current (NC) Non-Standard Interactions (NSI) of neutrinos with matter fields. Neutrino oscillation experiments along with the Elastic Coherent $ν$ Nucleus Scattering (CE$ν$NS) experiments already set strong bounds on all the flavor elements of the "vector" NC NSI. However, "axial" NC NSI can hide from these experiments. We show how a DUNE-like experiment can probe these couplings by studying NC Deep Inelastic Scattering (DIS) events. We find that strong bounds can be set on the axial NC NSI of neutrinos with the $u$, $d$, and $s$ quarks. We show that using both the near and far detectors, a DUNE-like experiment can significantly improve the present bounds on all the flavor elements.

Sterile neutrinos ($ν_s$s) are well-motivated and actively searched for hypothetical neutral particles that would mix with the Standard Model active neutrinos. They are considered prime warm dark matter (DM) candidates, typically when their mass is in the keV range, although they can also be hot or cold DM components. We discuss in detail the characteristics and phenomenology of $ν_s$s that minimally couple only to active neutrinos and are produced in the evaporation of early Universe primordial black holes (PBHs), a process we called "PBH sterile neutrinogenesis". Contrary to the previously studied $ν_s$ production mechanisms, this novel mechanism does not depend on the active-sterile mixing. The resulting $ν_s$s have a distinctive spectrum and are produced with larger energies than in typical scenarios. This characteristic enables $ν_s$s to be WDM in the unusual $0.3$ MeV to $0.3$ TeV mass range, if PBHs do not matter-dominate the Universe before evaporating. When PBHs matter-dominate before evaporating, the possible coincidence of induced gravitational waves associated with PBH evaporation and astrophysical X-ray observations from $ν_s$ decays constitutes a distinct signature of our scenario. constitutes a distinct signature of our scenario.

Ultralight dark matter with neutrino couplings is investigated in light of the long-baseline neutrino oscillation data in T2K and NO$ν$A experiments. The observed tension between T2K and NO$ν$A is shown to be ameliorated when ultralight dark matter of either scalar or vector form is taken into consideration. The best result is achieved with scalar dark matter which can alleviate the tension by 2.0$σ$ CL with flavour-universal couplings. We also consider scalar dark matter with flavour-general couplings and vector dark matter in $L_e - L_μ$ and $L_μ- L_τ$ cases. It is shown in all cases that the tension is relaxed by approximately 1.5$σ$-2.0$σ$ CL while the current experimental constraints can be evaded.

We investigate how superradiance affects the generation of baryon asymmetry in a universe with rotating primordial black holes, considering a scenario where a scalar boson is coupled to the heavy right-handed neutrinos. We identify the regions of the parameter space where the scalar production is enhanced due to superradiance. This enhancement, coupled with the subsequent decay of the scalar into right handed neutrinos, results in the non-thermal creation of lepton asymmetry. We show that successful leptogenesis is achieved for masses of primordial black holes in the range of order $O(0.1~{\rm g}) - O(10~{\rm g})$ and the lightest of the heavy neutrino masses, $M_N \sim O(10^{12})~{\rm GeV}$. Consequently, regions of the parameter space, which in the case of Schwarzchild PBHs were incompatible with viable leptogenesis, can produce the observed matter-antimatter asymmetry.

Primordial black holes~(PBHs) formed in the early Universe are well-motivated dark matter~(DM) candidates over a wide range of masses. These PBHs could emit detectable signals in the form of photons, electrons, and neutrinos through Hawking radiation. We consider the null observations of astrophysical $\barν_{e}$ flux from several neutrino detectors and set new constraints on the PBHs as the dominant DM component to be above $6.4\times10^{15}\,{\rm g}$. We also estimate the expected constraints with JUNO for the prospects in the near future. Lastly, we note that the diffuse supernova neutrino background~(DSNB) is an unavoidable isotropic background. We thus estimate the sensitivity floor for PBH parameter space due to the DSNB and show that it is challenging for neutrino detectors to identify PBHs as they constitute 100\% of the DM above a mass of 9$\times10^{15}$g.

The excess radio background detected by ARCADE 2 represents a puzzle within the standard cosmological model. There is no clear viable astrophysical solution, and therefore, it might indicate the presence of new physics. Radiative decays of a relic neutrino $ν_i$ (either $i=1$, or $i=2$, or $i=3$) into a sterile neutrino $ν_{\rm s}$, assumed to be quasi-degenerate, provide a solution that currently evades all constraints posed by different cosmological observations and reproduces very well the ARCADE 2 data. We find a very good fit to the ARCADE 2 data with best fit values $τ_i = 1.46 \times 10^{21}\,{\rm s}$ and $Δm_i = 4.0 \times 10^{-5}\,{\rm eV}$, where $τ_i$ is the lifetime and $Δm_i$ is the mass difference between the decaying active neutrino and the sterile neutrino. On the other hand, if relic neutrino decays do not explain ARCADE 2 data, then these place a stringent constraint $Δm_i^{3/2} τ_i \gtrsim 2 \times 10^{14}\,{\rm eV}^{3/2}\,{\rm s}$ in the range $1.4 \times 10^{-5} \, {\rm eV} < Δm_i < 2.5 \times 10^{-4}\,{\rm eV}$. The solution also predicts a stronger 21 cm absorption global signal than the predicted one from the $Λ$CDM model, with a contrast brightness temperature $T_{21} = -238^{+21}_{-20}\,{\rm mK}$ ($99\%$ C.L.) at redshift $z\simeq 17$. This is in mild tension with the even stronger signal found by the EDGES collaboration, $T_{21} = - 500^{+200}_{-500}\,{\rm mK} $, suggesting that this might have been overestimated, possibly receiving a contribution from some unidentified foreground source.

A dipole anisotropy in ultra-high-energy cosmic ray (UHECR) arrival directions, of extragalactic origin, is now firmly established at energies E > 8 EeV. Furthermore, the UHECR angular power spectrum shows no power at smaller angular scales than the dipole, apart from hints of possible individual hot or warm spots for energy thresholds $\gtrsim$40 EeV. Here, we exploit the magnitude of the dipole and the limits on smaller-scale anisotropies to place constraints on two quantities: the extragalactic magnetic field (EGMF) and the number density of UHECR sources or the volumetric event rate if UHECR sources are transient. We also vary the bias between the extragalactic matter and the UHECR source densities, reflecting whether UHECR sources are preferentially found in over- or under-dense regions, and find that little or no bias is favored. We follow Ding et al. (2021) in using the Cosmic Flows 2 density distribution of the local universe as our baseline distribution of UHECR sources, but we improve and extend that work by employing an accurate and self-consistent treatment of interactions and energy losses during propagation. Deflections in the Galactic magnetic field are treated using both the full JF12 magnetic field model, with random as well as coherent components, or just the coherent part, to bracket the impact of the GMF on the dipole anisotropy. This Large Scale Structure (LSS) model gives good agreement with both the direction and magnitude of the measured dipole anisotropy and forms the basis for simulations of discrete sources and the inclusion of EGMF effects.

The Extreme Universe Space Observatory on a Super Pressure Balloon 2, EUSO SPB2, mission was designed to take optical measurements of extensive air showers, EASs, from suborbital space. The EUSO SPB2 payload includes an optical Cherenkov Telescope, CT, which searches above and below the Earth's limb. Above the limb, the CT measures Cherenkov light from PeV scale EASs induced by cosmic rays. Below the limb, the CT searches for upwards going Cherenkov emission from PeV scale EASs induced by tau neutrinos, to follow up on astrophysical Targets of Opportunity, ToO. Target candidates include gamma ray bursts, tidal disruption events, and, after the start of the O4 obervation run from Ligo, Virgo, Kagra, binary neutron star mergers. Reported here is the selection and prioritization of relevant ToOs from alert networks such as the General Coordinates Network, Transient Name Server, and Astronomer Telegrams, and the translation to a viewing schedule for EUSO SPB2. EUSO SPB2 launched on a NASA super pressure balloon in May of 2023 from Wanaka, NZ.

Recently, several models have been suggested to reduce the tension between Gallium and reactor antineutrino spectral ratio data which is found in the framework of 3+1 active-sterile neutrino mixing. Among these models, we consider the extensions of 3+1 mixing with a finite wavepacket size, or the decay of the heaviest neutrino $ν_4$, or the possibility to have a broad $ν_4$ mass distribution. We consider the reactor antineutrino rate data and we show that these models cannot liminate the tension between Gallium and reactor rate data that is found in the 3+1 neutrino mixing framework. Indeed, we show that the parameter goodness of fit remains small. We consider also a model which explains the Gallium Anomaly with non-standard decoherence in the framework of three-neutrino mixing. We find that it is compatible with the reactor rate data.

The upcoming European Spallation Source (ESS) will soon provide the most intense neutrino source in the world. We propose the Search for Hidden Neutrinos at the ESS (SHiNESS) experiment, highlighting its unique opportunities to search for the existence of sterile neutrinos across a wide range of scales: anomalous oscillations at short baselines; non-unitarity mixing in the active neutrino sector; or an excess of events with multiple leptons in the final state, produced in the decay of heavy neutrinos. The baseline design of the detector comprises an active volume filled with 42 ton of liquid scintillator, located 25 m far from the ESS beam target. We show that SHiNESS will be able to considerably improve current global limits for the three cases outlined above. Although in this work we focus on new physics in the neutrino sector, the proposed setup may also be used to search for signals from weakly interacting particles in a broader context.

We determine the solar neutrino fluxes from the global analysis of the most up-to-date terrestrial and solar neutrino data including the final results of the three phases of Borexino. The analysis are performed in the framework of three-neutrino mixing with and without accounting for the solar luminosity constraint. We discuss the independence of the results on the input from the Gallium experiments. The determined fluxes are then compared with the predictions provided by the latest Standard Solar Models. We quantify the dependence of the model comparison with the assumptions about the normalization of the solar neutrino fluxes produced in the CNO-cycle as well as on the particular set of fluxes employed for the model testing.

We investigate the potential of future tau neutrino experiments for identifying the $ν_τ$ appearance in probing secret neutrino interactions. The reference experiments include the DUNE far detector utilizing the atmospheric data, which is for the first time in probing the secret interactions, the Forward Liquid Argon Experiment (FLArE100) detector at the Forward Physics Facility (FPF), and emulsion detector experiments such as SND@LHC, AdvSND, FASER$ν$2, and SND@SHiP. For concreteness, we consider a reference scenario in which the hidden interactions among the neutrinos are mediated by a single light gauge boson $Z'$ with a mass at most below the sub-GeV scale and an interaction strength $g_{αβ}$ between the active neutrinos. We confirm that these experiments have the capability to significantly enhance the current sensitivities on $g_{αβ}$ for $m_{Z'} \lesssim 500$ MeV due to the production of high energy neutrinos and excellent ability to detect tau neutrinos. Our analysis highlights the crucial role of downward-going DUNE atmospheric data in the search for secret neutrino interactions because of the rejection of backgrounds dominated in the upward-going events. Specifically, 10 years of DUNE atmospheric data can provide the best sensitivities on $g_{αβ}$ which is about two orders of magnitude improvement. In addition, the beam-based experiments such as FLArE100 and FASER$ν$2 can improve the current constraint on $g_{eτ}$ and $g_{μτ}$ by more than an order of magnitude after the full running of the high luminosity LHC with the integrated luminosity of 3 ab$^{-1}$. For $g_{eμ}$ and $g_{ee}$ the SHiP experiment can play the most important role in the high energy region of $E> few~100$ MeV.

We show that a mass-varying neutrino model driven by scalar field dark energy relaxes the existing upper bound on the current neutrino mass to ${\sum m_ν< 0.72}$ eV. We extend the standard $Λ$ cold dark matter model by introducing two parameters: the rate of change of the scalar field with the number of $e$-folds and the coupling between neutrinos and the field. We investigate how they affect the matter power spectrum, the cosmic microwave background anisotropies and its lensing potential. The model is tested against Planck observations of temperature, polarization, and lensing, combined with baryon acoustic oscillation measurements that constrain the background evolution. The results indicate that small couplings favor a cosmological constant, while larger couplings favor a dynamical dark energy, weakening the upper bound on current neutrino masses.

We propose the first practical method to detect atmospheric tau neutrino appearance at sub-GeV energies, which would be an important test of $ν_μ\rightarrow ν_τ$ oscillations and of new-physics scenarios. In the Jiangmen Underground Neutrino Observatory (JUNO; starts in 2024), active-flavor neutrinos eject neutrons from carbon via neutral-current quasielastic scattering. This produces a two-part signal: the prompt part is caused by the scattering of the neutron in the scintillator, and the delayed part by its radiative capture. Such events have been observed in KamLAND, but only in small numbers and were treated as a background. With $ν_μ\rightarrow ν_τ$ oscillations, JUNO should measure a clean sample of 55 events/yr; with simple $ν_μ$ disappearance, this would instead be 41 events/yr, where the latter is determined from Super-Kamiokande charged-current measurements at similar neutrino energies. Implementing this method will require precise laboratory measurements of neutrino-nucleus cross sections or other developments. With those, JUNO will have $5σ$ sensitivity to tau-neutrino appearance in 5 years exposure, and likely sooner.

Sterile neutrinos with masses up to $\mathcal{O} (100)$ MeV can be copiously produced in a supernova (SN) core, through the mixing with active neutrinos. In this regard the SN 1987A detection of neutrino events has been used to put constraints on active-sterile neutrino mixing, exploiting the well-known SN cooling argument. We refine the calculation of this limit including neutral current interactions with nucleons, that constitute the dominant channel for sterile neutrino production. We also include, for the first time, the charged current interactions between sterile neutrinos and muons, relevant for the production of sterile neutrinos mixed with muon neutrinos in the SN core. Using the recent modified luminosity criterion, we extend the bounds to the case where sterile states are trapped in the stellar core. Additionally, we study the decays of heavy sterile neutrinos, affecting the SN explosion energy and possibly producing a gamma-ray signal. We also illustrate the complementarity of our new bounds with cosmological bounds and laboratory searches.

Core-collapse supernovae (SNe) are one of the most powerful cosmic sources of neutrinos, with energies of several MeV. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final states. Detecting these neutrinos from Earth and analyzing the emitted signals present a unique opportunity to explore the neutrino mass ordering problem. This research outlines the detection of neutrinos from SNe and their relevance in understanding the neutrino mass ordering. The focus is on developing a model-independent analysis strategy, achieved by comparing distinct detection channels in large underground detectors. The objective is to identify potential indicators of mass ordering within the neutrino sector. Additionally, a thorough statistical analysis is performed on the anticipated neutrino signals for both mass orderings. Despite uncertainties in supernova explosion parameters, an exploration of the parameter space reveals an extensive array of models with significant sensitivity to differentiate between mass orderings. The assessment of various observables and their combinations underscores the potential of forthcoming supernova observations in addressing the neutrino mass ordering problem.

Since neutrino oscillation was observed, several experiments have been built to measure its parameters. NO$ν$A and T2K are two long-baseline experiments dedicated to measuring mainly the mixing angle $θ_{23}$, the charge-parity conjugation phase $δ_{\rm CP}$, and the mass ordering. However, there is a tension in current data. The T2K allowed region is in conflict with the region allowed by NO$ν$A. We propose a nonstandard charged current interaction (CC-NSI) in neutrino production to relieve this tension. The CC-NSI is computed through quantum field theory (QFT) formalism, where we derive perturbative analytical formulae considering CC-NSI in the pion decay. Within this new approach, we can alleviate NO$ν$A and T2K tension for a CC-NSI complex parameters of order $10^{-3}$. We show the new phase has a degeneracy to the Dirac CP phase of the form $δ_{\rm CP} \pm φ= 1.5π$ being a possible source of violation of charge-parity symmetry.

Our study investigates the complex interaction between active neutrinos and the ultralight bosonic dark matter halo surrounding the Sun. This halo extends over several solar radii due to the Sun's gravitational field, and we represent it as a coherent oscillating classical field configuration of bosonic dark matter particles that vary in time. Our investigation has revealed that, based on the available solar neutrino flux data, these novel models do not surpass the performance of the conventional neutrino flavour oscillation model. Furthermore, we discuss how next-generation solar neutrino detectors have the potential to provide evidence for the existence or absence of the ultralight dark matter halo.

Stopped-pion experiments that measure coherent elastic neutrino-nucleus scattering (CE$ν$NS) are sensitive to sterile neutrinos via disappearance. Using timing and energy spectra to perform flavor decomposition, we show that the delayed electron neutrino component provides an independent test of short-baseline anomalies that hint at $\sim$ eV-mass sterile neutrinos. Dedicated experiments will be sensitive to nearly the entire sterile neutrino parameter space consistent with short-baseline data.

In this paper we study non-standard interactions mediated by a scalar field (SNSI) in the context of ESSnuSB experiment. In particular we study the capability of ESSnuSB to put bounds on the SNSI parameters and also study the impact of SNSI in the measurement of the leptonic CP phase $δ_{\rm CP}$. Existence of SNSI modifies the neutrino mass matrix and this modification can be expressed in terms of three diagonal real parameters ($η_{ee}$, $η_{μμ}$ and $η_{ττ}$) and three off-diagonal complex parameters ($η_{e μ}$, $η_{eτ}$ and $η_{μτ}$). Our study shows that the upper bounds on the parameters $η_{μμ}$, $η_{ττ}$ and $η_{μτ}$ depend upon how $Δm^2_{31}$ is minimized in the theory. However, this is not the case when one tries to measure the impact of SNSI on $δ_{\rm CP}$. Further, we show that the CP sensitivity of ESSnuSB can be completely lost for certain values of $η_{ee}$ and $η_{μτ}$ for which the appearance channel probability becomes independent of $δ_{\rm CP}$.

The neutrinos in the diffuse supernova neutrino background (DSNB) travel over cosmological distances and this provides them with an excellent opportunity to interact with dark relics. We show that a cosmologically-significant relic population of keV-mass sterile neutrinos with strong self-interactions could imprint their presence in the DSNB. The signatures of the self-interactions would be ``dips" in the otherwise smooth DSNB spectrum. Upcoming large-scale neutrino detectors, for example Hyper-Kamiokande, have a good chance of detecting the DSNB and these dips. If no dips are detected, this method serves as an independent constraint on the sterile neutrino self-interaction strength and mixing with active neutrinos. We show that relic sterile neutrino parameters that evade X-ray and structure bounds may nevertheless be testable by future detectors like TRISTAN, but may also produce dips in the DSNB which could be detectable. Such a detection would suggest the existence of a cosmologically-significant, strongly self-interacting sterile neutrino background, likely embedded in a richer dark sector.

The Forward Physics Facility (FPF) plans to use neutrinos produced at the Large Hadron Collider (LHC) to make a variety of measurements at previously unexplored TeV energies. Its primary goals include precision measurements of the neutrino cross section and using the measured neutrino flux both to uncover information about far-forward hadron production and to search for various beyond standard model scenarios. However, these goals have the potential to conflict: extracting information about the flux or cross section relies upon an assumption about the other. In this manuscript, we demonstrate that the FPF can use the low-$ν$ method -- a technique for constraining the flux shape by isolating neutrino interactions with low energy transfer to the nucleus -- to break this degeneracy. We show that the low-$ν$ method is effective for extracting the $ν_μ$ flux shape, in a model-independent way. We discuss its application for extracting the $\barν_μ$ flux shape, but find that this is significantly more model dependent. Finally, we explore the precision to which the $ν_μ$ flux shape could be constrained at the FPF, for a variety of proposed detector options. We find that the precision would be sufficient to discriminate between various realistic flux models.

We explore the possibility that high-energy (HE) neutrinos produced from choked jets can be annihilated with low-energy (LE) neutrinos emitted from the accretion disk around a black hole in binary neutron star mergers and rare core-collapse supernovae. For HE neutrinos produced close to the stellar center ($\lesssim 10^{9}-10^{12}$ cm), we find that the emerging all-flavor spectrum for neutrinos of $E\gtrsim 0.1-1$ PeV could be modified by a factor $E^{-n}$ with $n\gtrsim 0.4-0.5$ under realistic conditions. Flavor evolution of LE neutrinos does not affect this result but can change the emerging flavor composition of HE neutrinos. As a consequence, the above annihilation effect may need to be considered for HE neutrinos produced from choked jets at small radii. We briefly discuss the annihilation effects for different HE neutrino production models and point out that such effects could be tested through precise measurements of the diffuse neutrino spectrum and flavor composition.

The neutrino mixing parameters are expected to have RG running effect in the presence of new physics. If the momentum transfers at production and detection mismatch with each other, the oscillation probabilities are generally modified and become dependent on not just the neutrino energy but also the momentum transfer. Even in the limit of vanishing baseline, the transition probability for the appearance channel is interestingly not zero. This would significantly affect the sensitivity of the genuine leptonic Dirac CP phase. We further explore the possibility of combing the long- and short-baseline neutrino experiments to constrain such RG running effect for the purpose of guaranteeing the CP measurement. To simulate the double dependence on the neutrino energy and momentum transfer, we extend the usual GLoBES simulation of fixed baseline experiments and use a two-dimensional $χ^2$ analysis to obtain sensitivities.

The mass-induced neutrino oscillation is a well established phenomenon that is based on the unitary mixing among three light active neutrinos. Remarkable precision on neutrino mixing parameters over the last decade or so has opened up the prospects for testing the possible non-unitarity of the standard 3$ν$ mixing matrix, which may arise in the seesaw extensions of the Standard Model due to the admixture of three light active neutrinos with heavy isosinglet neutrinos. Because of this non-unitary neutrino mixing (NUNM), the oscillation probabilities among the three active neutrinos would be altered as compared to the probabilities obtained assuming a unitary 3$ν$ mixing matrix. In such a NUNM scenario, neutrinos can experience an additional matter effect due to the neutral current interactions with the ambient neutrons. Atmospheric neutrinos having access to a wide range of energies and baselines can experience a significant modifications in Earth's matter effect due to NUNM. In this paper, we study in detail how the NUNM parameter $α_{32}$ affects the muon neutrino and antineutrino survival probabilities in a different way. Then, we place a comparable and complementary constraint on $α_{32}$ in a model independent fashion using the proposed 50 kt magnetized Iron Calorimeter (ICAL) detector under the India-based Neutrino Observatory (INO) project, which can efficiently detect the atmospheric $ν_μ$ and $\barν_μ$ separately in the multi-GeV energy range. Further, we discuss the advantage of charge identification capability of ICAL and the impact of uncertainties in oscillation parameters while constraining $α_{32}$. We also compare the $α_{32}$ sensitivity of ICAL with that of future long-baseline experiments DUNE and T2HK in isolation and combination.

Neutrino experiments, in the next years, aim to determine with precision all the six parameters of the three-neutrino standard paradigm. The complete success of the experimental program is, nevertheless, attached to the non-existence (or at least smallness) of Non-Standard Interactions (NSI). In this work, anticipating the data taken from long-baseline neutrino experiments, we map all the weakly coupled theories that could induce sizable NSI, with the potential to be determined in these experiments, in particular DUNE. Once present constraints from other experiments are taken into account, in particular charged-lepton flavor violation, we find that only models containing leptoquarks (scalar or vector) and/or neutral isosinglet vector bosons are viable. We provide the explicit matching formulas connecting weakly coupled models and NSI, both in propagation and production. Departing from the weakly coupled completion with masses at TeV scale, we also provide a global fit on all NSI for DUNE, finding that NSI smaller than $10^{-2}$ cannot be probed even in the best-case scenario.

The study of neutrino non-standard interactions (NSI) is a well-motivated phenomenological scenario to explore new physics beyond the Standard Model. The possible scalar coupling of neutrinos ($ν$) with matter is one of such new physics scenarios that appears as a sub-dominant effect that can impact the $ν$-oscillations in matter. The presence of scalar NSI introduces an additional contribution directly to the $ν$-mass matrix in the interaction Hamiltonian and subsequently to the $ν$-oscillations. This indicates that scalar NSI may have a significant impact on measurements related to $ν$-oscillations e.g. leptonic CP phase $(δ_{CP})$, $θ_{23}$ octant and neutrino mass ordering (MO). The linear scaling of the effects of scalar NSI with matter density also motivates its exploration in long-baseline (LBL) experiments. In this paper, we study the impact of a scalar-mediated NSI on the MO sensitivity of DUNE, HK and HK+KNO, which are upcoming LBL experiments. We study the impact on MO sensitivities at these experiments assuming that scalar NSI parameters are present in nature and is known from other non-LBL experiments. We observe that the presence of diagonal scalar NSI elements can significantly affect the $ν$-mass ordering sensitivities. We then also combine the data from DUNE with HK and HK+KNO to explore possible synergy among these experiments in a wider parameter space. We also observe a significant enhancement in the MO sensitivities for the combined analysis.

In this work, we consider the possible presence of a large population of millisecond pulsars in the Galactic Centre. Their direct detection would be challenging due to severe pulse broadening caused by scattering of radiation. We propose a new method to constrain their population with neutrino imaging of the Galactic Centre. Millisecond pulsars are proposed cosmic-ray accelerators. The high-energy protons they produce will collide with the baryonic matter in the central molecular zone to create charged and neutral pions that decay into neutrinos and $γ$-rays, respectively. The specific neutrino and $γ$-ray fluxes must be below their corresponding observed values, allowing us to put a conservative upper limit on the millisecond pulsar population of N_MSP < 10,000 within a galacto-centric radius of 20 pc. This upper limit is sensitive to the proton acceleration efficiency of the pulsars, but is less dependent on the particle injection spectral index and the choice of mass tracers. The population will be better constrained when high resolution neutrino observations of the Galactic Centre become available. The presence of these millisecond pulsars can account for the $γ$-ray excess in the Galactic Centre.

A sub-component of dark matter with a short collision length compared to a planetary size leads to efficient accumulation of dark matter in astrophysical bodies. We analyze possible neutrino signals from the annihilation of such dark matter and conclude that in the optically thick regime for dark matter capture, the Earth provides the largest neutrino flux. Using the results of the existing searches, we consider two scenarios for the neutrino flux, from stopped mesons and prompt higher-energy neutrinos. In both cases we exclude some previously unexplored parts of the parameter space (dark matter mass, its abundance, and the scattering cross section on nuclei) by recasting the existing neutrino searches.

We show that ATLAS, a collider detector, can measure the flux of high-energy supernova neutrinos, which can be produced from days to months after the explosion. Using Monte Carlo simulations for predicted fluxes, we find at most $\mathcal{O}(0.1-1)$ starting events and $\mathcal{O}(10-100)$ throughgoing events from a supernova 10 kpc away. Possible Galactic supernovae from Betelgeuse and Eta Carinae are further analyzed as demonstrative examples. We argue that even with limited statistics, ATLAS has the ability to discriminate among flavors and between neutrinos and antineutrinos, making it an unique neutrino observatory so far unmatched in this capability.

The origin of the observed diffuse neutrino flux is not yet known. Studies of the relative flavour content of the neutrino flux detected at Earth can give information on the production mechanisms at the sources and on flavour mixing, complementary to measurements of the spectral index and normalisation. Here we demonstrate the effects of neutrino fluxes with different spectral shapes and different initial flavour compositions dominating at different energies, and we study the sensitivity of future measurements with the IceCube Neutrino Observatory. Where one kind of flux gives way to another, this shows up as a non-trivial energy dependence in the flavour compositions. We explore this in the context of slow-jet supernovae and magnetar-driven supernovae -- two examples of astrophysical sources where charm production may be effective. Using current best-fit neutrino mixing parameters and their projected 2040 uncertainties, we use event ratios of different event morphologies at IceCube to illustrate the possibilities of distinguishing the energy dependence of neutrino flavour ratios.

The absence of a breakthrough in directly observing dark matter (DM) through prominent large-scale detectors motivates the development of novel tabletop experiments probing more exotic regions of the parameter space. If DM contains ultralight bosonic particles, they would behave as a classical wave and could manifest through an oscillating force on baryonic matter that is coherent over $\sim 10^6$ periods. Our Helium ultraLIght dark matter Optomechanical Sensor (HeLIOS) uses the high-$Q$ acoustic modes of superfluid helium-4 to resonantly amplify this signal. A superconducting re-entrant microwave cavity enables sensitive optomechanical readout ultimately limited by thermal motion at millikelvin temperatures. Pressurizing the helium allows for the unique possibility of tuning the mechanical frequency to effectively broaden the DM detection bandwidth. We demonstrate the working principle of our prototype HeLIOS detector and show that future generations of HeLIOS could explore unconstrained parameter space for both scalar and vector ultralight DM after just an hour of integration time.

A recently published method for solving the neutrino evolution equation with constant matter density is further refined and used to lay out an exact algorithm for computing oscillation probabilities, which is moderately faster than previous methods when looping through neutrinos of different energies. In particular, the three examples of $\overset{\scriptscriptstyle{(-)}}ν_e$ survival, $\overset{\scriptscriptstyle{(-)}}ν_μ$ survival and $\overset{\scriptscriptstyle{(-)}}ν_e$ appearance probabilities are written in terms of mixing angles, mass differences and matter electron density. A program based on this new method is found to be roughly twice as fast as, and in agreement with, the leading GLoBES package. Furthermore, the behaviour of all relevant effective parameters is sketched out in terms of a range of neutrino energies, or matter electron densities. For instance, the $\overset{\scriptscriptstyle{(-)}}ν_e$ survival probability in constant matter density is found to have no dependence on the mixing angle $θ_{23}$ or the CP-violating phase $δ_{13}$.

Long-baseline neutrino oscillation experiments offer a unique laboratory to test the fundamental Lorentz symmetry, which is heart of both the standard model of particle and general relativity theory. Deviations from the standard neutrino oscillation or the sidereal modulation in neutrino events will smoking-gun experimental signature of Lorentz and CPT violation. In this study, we investigate the impact of the sidereal effect on standard neutrino oscillation measurements within the context of the NOνA experiment. Additionally, we assess the sensitivity of the NOνA experiment to detect Lorentz-violating interactions, taking into account the sidereal effect. Furthermore, we highlight potential of the NOνA experiment to set the new constraints on anisotropic Lorentz-violating parameters.

We present an extra condition by which the size of the uncertainty associated with the diagonal elements in the quark mixing matrix can be further constrained when the matrix is parameterized by a combination of three mixing angles and a Dirac phase. Then we discuss how the correlations among the uncertainties of the diagonal emenets can be used when we address issues such as the tension in the first row and the column of the matrix and discuss its implications.

We predict that neutrino sources following the matter distribution of the universe result in an anisotropy in the neutrino sky imprinted by the local large-scale structure. We calculate the level of this anisotropy and explore how it depends on the cosmological evolution of neutrino sources. We show how the level of anisotropy can be amplified when a cutoff in the neutrino spectrum is considered, introducing an effective neutrino horizon. This effect might allow for future neutrino detectors to measure a neutrino anisotropy associated with the local large-scale structure. Measurement of the level of this anisotropy along with features of the neutrino spectrum will allow observers to constrain the cosmological evolution of neutrino sources, which at ultrahigh energies (UHEs) are also expected to be the sources of UHE cosmic rays.

Solar antineutrinos are absent in the standard solar model prediction. Consequently, solar antineutrino searches emerge as a powerful tool to probe new physics capable of converting neutrinos into antineutrinos. In this study, we highlight that neutrino self-interactions, recently gaining considerable attention due to their cosmological and astrophysical implications, can lead to significant solar antineutrino production. We systematically explore various types of four-fermion effective operators and light scalar mediators for neutrino self-interactions. By estimating the energy spectra and event rates of solar antineutrinos at prospective neutrino detectors such as JUNO, Hyper-Kamiokande, and THEIA, we reveal that solar antineutrino searches can impose stringent constraints on neutrino self-interactions and probe the parameter space favored by the Hubble tension.

We investigate the sensitivity of the FASER$ν$ detector, a novel experimental setup at the LHC, to probe and constrain generalized neutrino interactions (GNI). Employing a comprehensive theoretical framework, we model the effects of generalized neutrino interactions on neutrino-nucleon deep inelastic scattering processes within the FASER$ν$ detector. By considering all the neutrino channels produced at the LHC, we perform a statistical analysis to determine the sensitivity of FASER$ν$ to constrain these interactions. Our results demonstrate that FASER$ν$ can place stringent constraints on the GNI effective couplings. Additionally, we study the relation between GNI and a minimal Leptoquark model where the SM is augmented by a singlet Leptoquark with hypercharge $1/3$. We have found that the sensitivities for various combinations of the Leptoquark Yukawa couplings are approximately $\mathcal{O}(1)$, particularly when considering a Leptoquark mass in the TeV range.

The observation of an astrophysical neutrino flux in IceCube and its detection capability to separate between the different neutrino flavors has led IceCube to constraint the flavor content of this flux. IceCube-Gen2 is the planned extension of the current IceCube detector, which will be about 8 times larger than the current instrumented volume. In this work, we study the sensitivity of IceCube-Gen2 to the astrophysical neutrino flavor composition and investigate its tau neutrino identification capabilities. We apply the IceCube analysis on a simulated IceCube-Gen2 dataset that mimics the High Energy Starting Event (HESE) classification. Reconstructions are performed using sensors that have 3 times higher quantum efficiency and isotropic angular acceptance compared to the current IceCube optical modules. We present the projected sensitivity for 10 years of data on constraining the flavor ratio of the astrophysical neutrino flux at Earth by IceCube-Gen2.

The three kinds of parameter degeneracy in neutrino oscillation, the intrinsic, sign and octant degeneracy, form an eight-fold degeneracy. The nature of this eight-fold degeneracy can be visualized on the ($\sin^22θ_{13}$, $1/\sin^2θ_{23}$)-plane, through quadratic curves defined by $P(ν_μ\toν_e)=$ const. and $P(\barν_μ\to\barν_e)=$ const., along with a straight line $P(ν_μ\toν_μ)=$ const. After $θ_{13}$ was determined by reactor neutrino experiments, the intrinsic degeneracy in $θ_{13}$ transforms into an alternative octant degeneracy in $θ_{23}$, which can potentially be resolved by incorporating the value of $P(ν_μ\toν_μ)$. In this paper, we analytically discuss whether this octant parameter degeneracy is resolved or persists in the future long baseline accelerator neutrino experiments, such as T2HK, DUNE, T2HKK and ESS$ν$SB. It is found that the energy spectra near the first oscillation maximum are effective in resolving the octant degeneracy, whereas those near the second oscillation maximum are not.

The $S$ matrix rephasing invariance is one of the fundamental principles of quantum mechanics that originates in its probabilistic interpretation. For a given $S$ matrix which describes neutrino oscillation, one can define the two different rephased amplitudes $S_{αβ}^{ \text{Reph-1} } \equiv e^{ i (λ_{1} / 2E) x} S_{αβ}$ and $S_{αβ}^{ \text{Reph-2} } \equiv e^{ i (λ_{2} / 2E) x} S_{αβ}$, which are physically equivalent to each other, where $λ_{k} / 2E$ denotes the energy eigenvalue of the $k$-th mass eigenstate. We point out that the transformation of the reparametrization (Rep) symmetry obtained with ``Symmetry Finder'' maps $S_{αβ}^{ \text{Reph-1} }$ to $S_{αβ}^{ \text{Reph-2} }$, and vice versa, providing a local and manifest realization of the $S$ matrix rephasing invariance by the Rep symmetry of the 1-2 state exchange type. It is strongly indicative of quantum mechanical nature of the Rep symmetry. The rephasing and Rep symmetry relation, though its all-order treatment remains incomplete, is shown to imply absence of the pure 1-3 exchange symmetry in Denton~{\it et al.}~perturbation theory. It then triggers a study of convergence of perturbation series.

In this paper we have studied the phenomenon of non-standard interaction mediated by a scalar field (SNSI) in the context of P2SO experiment and compared its sensitivity with DUNE. In particular, we have studied the capability of these two experiments to put bounds on the diagonal SNSI parameters i.e., $η_{ee}$, $η_{μμ}$ and $η_{ττ}$ and studied the impact of these parameters on the determination of neutrino mass ordering, octant of $θ_{23}$ and CP violation (CPV). In our analysis we find that, the parameter $Δm^2_{31}$ has a non-trivial role if one wants estimate the bounds on $η_{μμ}$ and $η_{ττ}$ assuming SNSI does not exist in nature. Our results show that sensitivity of P2SO and DUNE to constraint $η_{μμ}$ and $η_{ττ}$ are similar whereas the sensitivity of DUNE is slightly better for $η_{ee}$. We find that the mass ordering and CPV sensitivities are mostly affected by $η_{ee}$ compared to $η_{μμ}$ and $η_{ττ}$ if one assumes SNSI exists in nature. On the other hand, octant sensitivity is mostly affected by $η_{μμ}$ and $η_{ττ}$. These sensitivities can be either higher or lower than the standard three flavour scenario depending on the relative sign of the SNSI parameters. Regarding the precision of atmospheric mixing parameters, we find that the precision of $θ_{23}$ deteriorates significantly in the presence of $η_{μμ}$ and $η_{ττ}$.

The neutrinoless double beta decay experimental effort continues to make tremendous progress with hopes of covering the inverted neutrino mass hierarchy in coming years and pushing from the quasi-degenerate hierarchy into the normal hierarchy. As neutrino oscillation data is starting to suggest that the mass ordering may be normal, we may well be faced with staring down the funnel of death: a region of parameter space in the normal ordering where -- for a particular cancellation among the absolute neutrino mass scale, the Majorana phases, and the oscillation parameters -- the neutrinoless double beta decay rate may be vanishingly small. To answer the question of whether this region of parameter space is theoretically preferred, we survey five broad categories of flavor model structures which make various different predictions for parameters relevant for neutrinoless double beta decay to determine how likely it is that the rate may be in this funnel region. We find that a non-negligible fraction of predictions surveyed are at least partially in the funnel region. Our results can guide model builders and experimentalists alike in focusing their efforts on theoretically motivated regions of parameter space.

Soon, a new generation of neutrino telescopes, presently under planning, will target the discovery of ultra-high-energy (UHE) neutrinos of cosmic origin, with energies higher than 100 PeV, that promise unique insight into astrophysics and particle physics. Yet, predictions of the UHE neutrino flux and interaction cross section -- whose measurement is co-dependent -- are laden with significant uncertainty that, if unaddressed, could misrepresent the capabilities to measure one or the other. To address this, we advocate for the joint measurement of the UHE neutrino spectrum and neutrino-nucleon cross section, including of their energy dependence, without assuming prior knowledge of either. We illustrate our methods by adopting empirical parametrizations of the neutrino spectrum, in forecasts geared to the planned radio array of the IceCube-Gen2 neutrino telescope. We warn against using simple parametrizations -- a simple power law or one augmented with an exponential cut-off -- that might fail to capture features of the spectrum that are commonplace in the predictions. We argue instead for the use of flexible parametrizations -- a piecewise power law or an interpolating polynomial -- that ensure accuracy. We report loose design targets for the detector energy and angular resolution that are compatible with those under present consideration.

Ultra-High Energy (UHE) neutrinos over $10^{16}$ eV have yet to be observed but the Askaryan Radio Array (ARA) is one in-ice neutrino observatory attempting to make this discovery. In anticipation of a thorough full-observatory and full-livetime neutrino search, we estimate how many neutrino events can be detected accounting for secondary interactions, which are typically ignored in UHE neutrino simulations. Using the NuLeptonSim and PyREx simulation frameworks, we calculate the abundance and usefulness of cascades viewed by multiple ARA stations and observations made of taus, muons, and neutrinos generated during and after initial neutrino cascades. Analyses that include these scenarios benefit from a considerable increase in effective area at key ARA neutrino energies, one example being a 30% increase in ARA's effective area when simulating taus and muons produced in $10^{19}$ eV neutrino interactions. These analysis techniques could be utilized by other in-ice radio neutrino observatories, as has been explored by NuRadioMC developers. Our contribution showcases full simulation results of neutrinos with energies $3\times10^{17}$ - $10^{21}$ eV and visualizations of interesting triggered event topologies.

We investigate the capture rate of the cosmic neutrino background on tritium within the Standard Model, extended to incorporate three right-handed singlet neutrinos with explicit lepton-number violation. We consider a scenario where the $6 \times 6$ neutrino mixing matrix factorizes into three independent $2 \times 2$ pairs and analyze the states produced from weak interactions just before neutrino decoupling. Taking into account the unrestricted Majorana mass scale associated with lepton number violation, spanning from the Grand Unification scale to Planck-suppressed values, we observe a gradual transition in the capture rate from a purely Majorana neutrino to a purely (pseudo) Dirac neutrino. We demonstrate that the capture rate is modified if the lightest active neutrino is relativistic, and this can be used to constrain the tiniest value of mass-squared difference $\sim 10^{-35}\,{\rm eV}^2$, between the active-sterile pair, probed so far. Consequently, the cosmic neutrino capture rate could become a promising probe for discerning the underlying mechanism responsible for generating neutrino masses.

The formation of the Earth remains an epoch with mysterious puzzles extending to our still incomplete understanding of the planet's potential origin and bulk composition. Direct confirmation of the Earth's internal heat engine was accomplished by the successful observation of geoneutrinos originating from uranium (U) and thorium (Th) progenies, manifestations of the planet's natural radioactivity dominated by potassium (40K) and the decay chains of uranium (238U) and thorium (232Th). This radiogenic energy output is critical to planetary dynamics and must be accurately measured for a complete understanding of the overall heat budget and thermal history of the Earth. Detecting geoneutrinos remains the only direct probe to do so and constitutes a challenging objective in modern neutrino physics. In particular, the intriguing potassium geoneutrinos have never been observed and thus far have been considered impractical to measure. We propose here a novel approach for potassium geoneutrino detection using the unique antimatter signature of antineutrinos to reduce the otherwise overwhelming backgrounds to observing this rarest signal. The proposed detection framework relies on the innovative LiquidO detection technique to enable positron (e+) identification and antineutrino interactions with ideal isotope targets identified here for the first time. We also provide the complete experimental methodology to yield the first potassium geoneutrino discovery.

Experimental bounds on the neutrino lifetime depend on the nature of the neutrinos and the details of the potentially new physics responsible for neutrino decay. In the case where the decays involve active neutrinos in the final state, the neutrino masses also qualitatively impact how these manifest themselves experimentally. In order to further understand the impact of nonzero neutrino masses, we explore how observations of solar neutrinos constrain a very simple toy model. We assume that neutrinos are Dirac fermions and there is a new massless scalar that couples to neutrinos such that a heavy neutrino - $ν_2$ with mass $m_2$ - can decay into a lighter neutrino - $ν_1$ with mass $m_1$ - and a massless scalar. We find that the constraints on the new physics coupling depend, sometimes significantly, on the ratio of the daughter-to-parent neutrino masses, and that, for large enough values of the new physics coupling, the "dark side" of the solar neutrino parameter space - $\sin^2θ_{12}\sim 0.7$ - provides a reasonable fit to solar neutrino data. Our results generalize to other neutrino-decay scenarios, including those that mediate $ν_2\toν_1\barν_3ν_3$ when the neutrino mass ordering is inverted mass and $m_2>m_1\gg m_3$, the mass of $ν_3$.

In this work, we investigate how multinucleon enhancement and RPA (Random Phase Approximation) suppression can affect the measurement of three unknown neutrino oscillation parameters - the CP-violating phase $δ_{CP}$, the octant of the atmospheric mixing angle $θ_{23}$, and the determination of the mass hierarchy, in the appearance channel of the NO$ν$A experiment. We include the presence of the detector effect as well in the analysis, which is crucial for capturing realistic experimental scenarios. We also conducted a comparison between the nuclear model Effective Spectral Function (calculated within the RFG model) with and without Transverse Enhancement in terms of sensitivity analysis. It is found that the analysis using our comprehensive model QE(+RPA)+2p2h along with Effective Spectral Function+Transverse Enhancement exhibits significantly enhanced sensitivity compared to the pure QE interaction process, in all the cases.Also, the higher octant of $θ_{23}$, the lower half plane of $δ_{CP}$, and the normal mass hierarchy (HO-LHP-NH) exhibit improved sensitivity, enabling a more precise determination of the corresponding parameters. Furthermore, it is also noted that improving the performance of the detector also improves the results. Thus, including multinucleon effects and improving detector efficiency have the potential to enhance the capabilities of the NO$ν$A (and other long baseline) experiment in conducting precise parameter studies.

We return to interpreting the historical SN~1987A neutrino data from a modern perspective. To this end, we construct a suite of spherically symmetric supernova models with the Prometheus-Vertex code, using four different equations of state and five choices of final baryonic neutron-star (NS) mass in the 1.36-1.93 M$_\odot$ range. Our models include muons and proto-neutron star (PNS) convection by a mixing-length approximation. The time-integrated signals of our 1.44 M$_\odot$ models agree reasonably well with the combined data of the four relevant experiments, IMB, Kam-II, BUST, and LSD, but the high-threshold IMB detector alone favors a NS mass of 1.7-1.8 M$_\odot$, whereas Kam-II alone prefers a mass around 1.4 M$_\odot$. The cumulative energy distributions in these two detectors are well matched by models for such NS masses, and the previous tension between predicted mean neutrino energies and the combined measurements is gone, with and without flavor swap. Generally, our predicted signals do not strongly depend on assumptions about flavor mixing, because the PNS flux spectra depend only weakly on antineutrino flavor. While our models show compatibility with the events detected during the first seconds, PNS convection and nucleon correlations in the neutrino opacities lead to short PNS cooling times of 5-9 s, in conflict with the late event bunches in Kam-II and BUST after 8-9 s, which are also difficult to explain by background. Speculative interpretations include the onset of fallback of transiently ejected material onto the NS, a late phase transition in the nuclear medium, e.g., from hadronic to quark matter, or other effects that add to the standard PNS cooling emission and either stretch the signal or provide a late source of energy. More research, including systematic 3D simulations, is needed to assess these open issues.

Ultralight bosons near rotating black holes can undergo significant growth through superradiant energy extraction, potentially reaching field values close to the Planck scale and transforming black holes into effective transducers for these fields. The interaction between boson fields and fermions may lead to parametric production or Schwinger pair production of fermions, with efficiencies significantly exceeding those of perturbative decay processes. Additionally, the spatial gradients of scalar clouds and the electric components of vector clouds can accelerate fermions, resulting in observable fluxes. This study considers both Standard Model neutrinos and dark sector fermions, which could contribute to boosted dark matter. Energy loss due to fermion emissions can potentially quench the exponential growth of the cloud, leading to a saturated state. This dynamic provides a framework for establishing limits on boson-neutrino interactions, previously constrained by neutrino self-interaction considerations. In the saturation phase, boson clouds have the capacity to accelerate fermions to TeV energies, producing fluxes that surpass those from atmospheric neutrinos near black holes. These fluxes open new avenues for observations through high-energy neutrino detectors like IceCube, as well as through dark matter direct detection efforts focused on targeted black holes.

In this note we describe how to complement the neutrino evolution matrix calculated at a given energy and trajectory with additional information which allows to reliably extrapolate it to nearby energies or trajectories without repeating the full computation. Our method works for arbitrary matter density profiles, can be applied to any propagation model described by an Hamiltonian, and exactly guarantees the unitarity of the evolution matrix. As a straightforward application, we show how to enhance the calculation of the theoretical predictions for experimentally measured quantities, so that they remain accurate even in the presence of fast neutrino oscillations. Furthermore, the ability to "move around" a given energy and trajectory opens the door to precise interpolation of the oscillation amplitudes within a grid of tabulated values, with potential benefits for the computation speed of Monte-Carlo codes. We also provide a set of examples to illustrate the most prominent features of our approach.

The IceCube South Pole Neutrino Observatory is a Cherenkov detector instrumented in a cubic kilometer of ice at the South Pole. IceCube's primary scientific goal is the detection of TeV neutrino emissions from astrophysical sources. At the lower center of the IceCube array, there is a subdetector called DeepCore, which has a denser configuration that makes it possible to lower the energy threshold of IceCube and observe GeV-scale neutrinos, opening the window to atmospheric neutrino oscillations studies. Advances in physics sensitivity have recently been achieved by employing Convolutional Neural Networks to reconstruct neutrino interactions in the DeepCore detector. In this contribution, the recent IceCube result from the atmospheric muon neutrino disappearance analysis using the CNN-reconstructed neutrino sample is presented and compared to the existing worldwide measurements.

Ultra-high energy cosmic rays (UHECRs) beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off provide us with a unique opportunity to understand the universe at extreme energies. Secondary GZK photons and GZK neutrinos associated with the same interaction are indeed interconnected and render access to multi-messenger analysis of UHECRs. The GZK photon flux is heavily attenuated due to the interaction with Cosmic Microwave Background (CMB) and the Extra-galactic Radio Background (ERB). The present estimate of the ERB comprising of several model uncertainties together with the ARCADE2 radio results in large propagation uncertainties in the GZK photon flux. On the other hand, the weakly interacting GZK neutrino flux is unaffected by these propagation effects. In this work, we make an updated estimate of the GZK photon and GZK neutrino fluxes considering a wide variation of both the production and propagation properties of the UHECR like, the spectral index, the cut-off energy of the primary spectrum, the distribution of sources and the uncertainties in the ERB estimation. We explore the detection prospects of the GZK fluxes with various present and upcoming UHECR and UHE neutrino detectors such as Auger, TA, GRAND, ANITA, ARA, IceCube and IceCube-Gen2. The predicted fluxes are found to be beyond the reach of the current detectors. In future, proposed IceCube-Gen2, Auger upgrade and GRAND experiments will have the sensitivity to the predicted GZK photon and GZK neutrino fluxes. Such detection can put constraints on the UHECR source properties and the propagation effects due to the ERB. We also propose an indirect limit on the GZK photon flux using the neutrino-photon connection for any future detection of GZK neutrinos by the IceCube-Gen2 detector. We find this limit to be consistent with our GZK flux predictions.

Neutrinos are perhaps the most elusive known particles in the universe. We know they have some nonzero mass, but unlike all other particles, the absolute scale remains unknown. In addition, their fundamental nature is uncertain; they can either be their own antiparticles or exist as distinct neutrinos and antineutrinos. The observation of the hypothetical process of neutrinoless double-beta ($0νββ$) decay would at once resolve both questions, while providing a strong lead in understanding the abundance of matter over antimatter in our universe. In the scenario of light-neutrino exchange, the decay rate is governed by, and thereby linked to the effective mass of the neutrino via, the theoretical nuclear matrix element (NME). In order to extract the neutrino mass, if a discovery is made, or to assess the discovery potential of next-generation searches, it is essential to obtain accurate NMEs for all isotopes of experimental interest. However, two of the most important cases, $^{130}$Te and $^{136}$Xe, lie in the heavy region and have only been accessible to phenomenological nuclear models. In this work we utilize powerful advances in ab initio nuclear theory to compute NMEs from the underlying nuclear and weak forces driving this decay, including the recently discovered short-range component. We find that ab initio NMEs are generally smaller than those from nuclear models, challenging the expected reach of future ton-scale searches as well as claims to probe the inverted hierarchy of neutrino masses. With this step, ab initio calculations with theoretical uncertainties are now feasible for all isotopes relevant for next-generation $0νββ$ decay experiments.

Neutrino-neutrino scattering could have a large secret component that would turn neutrinos within a supernova (SN) core into a self-coupled fluid. Neutrino transport within the SN core, emission from its surface, expansion into space, and the flux spectrum and time structure at Earth might all be affected. We examine these questions from first principles. First, diffusive transport differs only by a modified spectral average of the interaction rate. We next study the fluid energy transfer between a hot and a cold blackbody surface in plane-parallel and spherical geometry. The key element is the decoupling process within the radiating bodies, which themselves are taken to be isothermal. For a zero-temperature cold plate, mimicking radiation into free space by the hot plate, the energy flux is 3--4\% smaller than the usual Stefan-Boltzmann Law. The fluid energy density just outside the hot plate is numerically 0.70 of the standard case, the outflow velocity is the speed of sound $v_s=c/\sqrt{3}$, conspiring to a nearly unchanged energy flux. Our results provide the crucial boundary condition for the expansion of the self-interacting fluid into space, assuming an isothermal neutrino sphere. We also derive a dynamical solution, assuming the emission suddenly begins at some instant. A neutrino front expands in space with luminal speed, whereas the outflow velocity at the radiating surface asymptotically approaches $v_s$ from above. Asymptotically, one thus recovers the steady-state emission found in the two-plate model. A sudden end to neutrino emission leads to a fireball with constant thickness equal to the duration of neutrino emission.

When hypothetical neutrino secret interactions ($ν$SI) are large, they form a fluid in a supernova (SN) core, flow out with sonic speed, and stream away as a fireball. For the first time, we tackle the complete dynamical problem and solve all steps, systematically using relativistic hydrodynamics. The impact on SN physics and the neutrino signal is remarkably small. For complete thermalization within the fireball, the observable spectrum changes in a way that is independent of the coupling strength. One potentially large effect beyond our study is quick deleptonization if $ν$SI violate lepton number. By present evidence, however, SN physics leaves open a large region in parameter space, where laboratory searches and future high-energy neutrino telescopes will probe $ν$SI.

We report the first measurement of CNO solar neutrinos by Borexino that uses the Correlated Integrated Directionality (CID) method, exploiting the sub-dominant Cherenkov light in the liquid scintillator detector. The directional information of the solar origin of the neutrinos is preserved by the fast Cherenkov photons from the neutrino scattered electrons, and is used to discriminate between signal and background. The directional information is independent from the spectral information on which the previous CNO solar neutrino measurements by Borexino were based. While the CNO spectral analysis could only be applied on the Phase-III dataset, the directional analysis can use the complete Borexino data taking period from 2007 to 2021. The absence of CNO neutrinos has been rejected with >5σ credible level using the Bayesian statistics. The directional CNO measurement is obtained without an external constraint on the $^{210}$Bi contamination of the liquid scintillator, which was applied in the spectral analysis approach. The final and the most precise CNO measurement of Borexino is then obtained by combining the new CID-based CNO result with an improved spectral fit of the Phase-III dataset. Including the statistical and the systematic errors, the extracted CNO interaction rate is $R(\mathrm{CNO})=6.7^{+1.2}_{-0.8} \, \mathrm{cpd/100 \, tonnes}$. Taking into account the neutrino flavor conversion, the resulting CNO neutrino flux at Earth is $Φ_\mathrm{CNO}=6.7 ^{+1.2}_{-0.8} \times 10^8 \, \mathrm{cm^{-2} s^{-1}}$, in agreement with the high metallicity Standard Solar Models. The results described in this work reinforce the role of the event directional information in large-scale liquid scintillator detectors and open up new avenues for the next-generation liquid scintillator or hybrid neutrino experiments.

Kerr black holes radiate neutrinos in an asymmetric pattern, preferentially in the lower hemisphere relative to the black hole's rotation axis, while antineutrinos are predominantly produced in the upper hemisphere. Leveraging this asymmetric emission, we explore the potential of high-energy, $E_ν\gtrsim 1$ TeV, neutrino and antineutrino detection to reveal crucial characteristics of an evaporating primordial black hole at the time of its burst when observed near Earth. We improve upon previous calculations by carefully accounting for the non-isotropic particle emission, as Earth occupies a privileged angle relative to the black hole's rotation axis. Additionally, we investigate the angular dependence of primary and secondary photon spectra and assess the evaporating black hole's time evolution during the final explosive stages of its lifetime. Since photon events outnumber neutrinos by about three orders of magnitude, we find that a neutrino measurement can aid in identifying the initial angular momentum and the black hole hemisphere facing Earth only for evaporating black holes within our solar system, at distances $\lesssim 10^{-4}$ pc, and observed during the final 100 s of their lifetime.

The Migdal effect predicts that a nuclear recoil interaction can be accompanied by atomic ionization, allowing many dark matter direct detection experiments to gain sensitivity to sub-GeV masses. We report the first direct search for the Migdal effect for M- and L-shell electrons in liquid xenon using 7.0$\pm$1.6 keV nuclear recoils produced by tagged neutron scatters. Despite an observed background rate lower than that of expected signals in the region of interest, we do not observe a signal consistent with predictions. We discuss possible explanations, including inaccurate predictions for either the Migdal rate or the signal response in liquid xenon. We comment on the implications for direct dark-matter searches and future Migdal characterization efforts.

The search for coherent elastic neutrino nucleus scattering (CE$ν$NS) using reactor antineutrinos represents a formidable experimental challenge, recently boosted by the observation of such a process at the Dresden-II reactor site using a germanium detector. This observation relies on an unexpected enhancement at low energies of the measured quenching factor with respect to the theoretical Lindhard model prediction, which implies an extra observable ionization signal produced after the nuclear recoil. A possible explanation for this additional contribution could be provided by the so-called Migdal effect, which however has never been observed. Here, we study in detail the impact of the Migdal contribution to the standard CE$ν$NS signal calculated with the Lindhard quenching factor, finding that the former is completely negligible for observed energies below $\sim 0.3\,\mathrm{keV}$ where the signal is detectable, and thus unable to provide any contribution to CE$ν$NS searches in this energy regime. To this purpose, we compare different formalisms used to describe the Migdal effect that intriguingly show a perfect agreement, making our findings robust.

Results from experiments like LSND and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations. In particular, it can give rise to additional degeneracies due to additional sterile parameters. For an eV scale sterile neutrino, the cosmological constraints dictate that the sterile state is heavier than the three active states. However, for lower masses of sterile neutrinos, it can be lighter than one and/or more of the three states. In such cases, the mass ordering of the sterile neutrinos also becomes unknown along with the mass ordering of the active states. In this paper, we explore the mass ordering sensitivity in the presence of a sterile neutrino assuming the mass squared difference $|\Delta_{41}|$ to be in the range $10^{-4} - 1$ eV$^2$. We study (i) how the ordering of the active states, i.e. the determination of the sign of $\Delta_{31}$ gets affected by the presence of a sterile neutrino in the above mass range, (ii) the possible determination of the sign of $\Delta_{41}$ for $\Delta_{41}$ in the range $10^{-4} - 0.1$ eV$^2$. This analysis is done in the context of a liquid argon detector using both beam neutrinos traveling a distance of 1300 km and atmospheric neutrinos which propagates through a distance ranging from 10 - 10000 km allowing resonant matter effects. Apart from presenting separate results from these sources, we also do a combined study and probe the synergy between these two in giving an enhanced sensitivity.

We investigate the sensitivities of the liquid scintillator counter (LSC) at Yemilab and JUNO to solar neutrino oscillation parameters, focusing on $θ_{12}$ and $Δm^2_{21}$. We compare the potential of JUNO with LSC at Yemilab utilizing both reactor and solar data in determining those parameters. We find that the solar neutrino data of LSC at Yemilab is highly sensitive to $θ_{12}$ enabling its determination with exceptional precision. Our study also reveals that if $Δm^2_{21}$ is larger, with a value close to the best fit value of KamLAND, JUNO reactor data will have about two times better precision than the reactor LSC at Yemilab. On the other hand, if $Δm^2_{21}$ is smaller and closer to the best fit value of solar neutrino experiments, the precision of the reactor LSC at Yemilab will be better than JUNO.

Upcoming neutrino telescopes promise a new window onto the interactions of neutrinos with matter at ultrahigh energies ($E_\nu = 10^7$-$10^{10}$ GeV), and the possibility to detect deviations from the Standard Model predictions. In this paper, we update previous predictions for the enhancement of the neutrino-nucleon cross-section for motivated leptoquark models and show the latest neutrino physics bound, as well as analyse the latest LHC pair production and Drell-Yan data, and flavour constraints (some of which were previously missed). We find that, despite the next generation of neutrino experiments probing the highest energies, they will not be enough to be competitive with collider searches.

One long-standing tension in the determination of neutrino parameters is the mismatched value of the solar mass square difference, $\Delta m_{21}^2$, measured by different experiments: the reactor antineutrino experiment KamLAND finds a best fit larger than the one obtained with solar neutrino data. Even if the current tension is mild ($\sim 1.5\sigma$), it is timely to explore if independent measurements could help in either closing or reassessing this issue. In this regard, we explore how a future supernova burst in our galaxy could be used to determine $\Delta m_{21}^2$ at the future Hyper-Kamiokande detector, and how this could contribute to the current situation. We study Earth matter effects for different models of supernova neutrino spectra and supernova orientations. We find that, if supernova neutrino data prefers the KamLAND best fit for $\Delta m_{21}^2$, an uncertainty similar to the current KamLAND one could be achieved. On the contrary, if it prefers the solar neutrino data best fit, the current tension with KamLAND results could grow to a significance larger than $5\sigma$. Furthermore, supernova neutrinos could significantly contribute to reducing the uncertainty on $\sin^2\theta_{12}$.

We present in this paper a public data release of an unprecedentedly-large set of core-collapse supernova (CCSN) neutrino emission models, comprising one hundred detailed 2D-axisymmetric radiation-hydrodynamic simulations evolved out to as late as ~5 seconds post-bounce and spanning a extensive range of massive-star progenitors. The motivation for this paper is to provide a physically and numerically uniform benchmark dataset to the broader neutrino detection community to help it characterize and optimize subsurface facilities for what is likely to be a once-in-a-lifetime galactic supernova burst event. With this release we hope to 1) help the international experiment and modeling communities more efficiently optimize the retrieval of physical information about the next galactic core-collapse supernova, 2) facilitate the better understanding of core-collapse theory and modeling among interested experimentalists, and 3) help further integrate the broader supernova neutrino community.

We investigate the observed muon deficit in air shower simulations when compared to ultrahigh-energy cosmic ray (UHECR) data. Gleaned from the observed enhancement of strangeness production in ALICE data, the associated $\pi \leftrightarrow K$ swap is taken as a cornerstone to resolve the muon puzzle via its corresponding impact on the shower evolution. We develop a phenomenological model in terms of the $\pi \leftrightarrow K$ swapping probability $F_s$. We provide a parametrization of $F_s (E^{\rm (proj)}, \eta)$ that can accommodate the UHECR data, where $E^{\rm (proj)}$ is the projectile energy and $\eta$ the pseudorapidity. We also explore a future game plan for model improvement using the colossal amount of data to be collected by LHC neutrino detectors at the Forward Physics Facility (FPF). We calculate the corresponding sensitivity to $F_s$ and show that the FPF experiments will be able to probe the model phase space.

A dedicated high-statistics measurement of the $^{71}$Ge half-life is found to be in accurate agreement with an accepted value of 11.43$\pm$0.03 d, eliminating a recently proposed route to bypass the "gallium anomaly" affecting several neutrino experiments. Our data also severely constrain the possibility of $^{71}$Ge decay to low-energy excited levels of the $^{71}$Ga daughter nucleus as a solution to this puzzle. Additional unpublished measurements of this decay are discussed. Following the incorporation of this new information, the gallium anomaly survives with high statistical significance.

In the standard interaction scenario, a direct measurement of absolute neutrino masses via neutrino oscillations is not feasible, as the oscillations depend only on the mass-squared differences. However, the presence of scalar non-standard interactions can introduce sub-dominant terms in the oscillation Hamiltonian that can directly affect the neutrino mass matrix and thereby making scalar NSI a unique tool for neutrino mass measurements. In this work, for the first time, we constrain the absolute masses of neutrinos by probing scalar NSI. We show that a bound on the lightest neutrino mass can be induced in the presence of scalar NSI at DUNE. We find that the lightest neutrino mass can be best constrained with $\eta_{\tau\tau}$ and $\eta_{\mu\mu}$ at $2\sigma$ C.L. for normal and inverted hierarchy respectively. This study suggests that scalar NSI can serve as an interesting avenue to constrain the absolute neutrino masses in long-baseline neutrino experiments via neutrino oscillations.

The interaction of neutrinos with ultralight scalar and vector dark matter backgrounds induce a modification of the neutrino dispersion relation. The effects of this modification are reviewed in the framework of asymmetric emission of neutrinos from the supernova core, and, in turn, of pulsar kicks. We consider the neutrino oscillations, focusing in particular to active-sterile conversion. The ultralight dark matter induced neutrino dispersion relation contains a term of the form $\delta {\bf \Omega}\cdot \hat{{\bf{p}}}$, where $\delta {\bf \Omega}$ is related to the ultralight dark matter field and $\hat{{\bf p}}$ is the unit vector along the direction of neutrino momentum. The relative orientation of ${\bf p}$ with respect to $\delta {\bf \Omega}$ affects the mechanism for the generation of the observed pulsar velocities. We obtain the resonance condition for the active-sterile neutrino oscillation in ultralight dark matter background and calculate the star parameters in the resonance surface so that both ultralight scalar and vector dark matter backgrounds can explain the observed pulsar kicks. The asymmetric emission of neutrinos in presence of ultralight dark matter background results gravitational memory signal which can be probed from the gravitational wave detectors. We also establish a connection between the ultralight dark matter parameters and the standard model extension parameter.

When neutrinos are propagating in ordinary matter, their coherent forward scattering off background particles results in the so-called Mikheyev-Smirnov-Wolfenstein (MSW) matter potential, which plays an important role in neutrino flavor conversions. In this paper, we present a complete one-loop calculation of the MSW matter potential in the Standard Model (SM). First, we carry out the one-loop renormalization of the SM in the on-shell scheme, where the electromagnetic fine-structure constant $α$, the weak gauge-boson masses $m^{}_W$ and $m^{}_Z$, the Higgs-boson mass $m^{}_h$ and the fermion masses $m^{}_f$ are chosen as input parameters. Then, the finite corrections to the scattering amplitudes of neutrinos with the electrons and quarks are calculated, and the one-loop MSW matter potentials are derived. Adopting the latest values of all physical parameters, we find that the relative size of one-loop correction to the charged-current matter potential of electron-type neutrinos or antineutrinos turns out to be $6\%$, whereas that to the neutral-current matter potential of all-flavor neutrinos or antineutrinos can be as large as $8\%$. The calculations are also performed in the $\overline{\rm MS}$ scheme and compared with previous results in the literature.

The Cosmic Neutrino Background (CNB) encodes a wealth of information, but has not yet been observed directly. To determine the prospects of detection and to study its information content, we reconstruct the phase-space distribution of local relic neutrinos from the three-dimensional distribution of matter within 200 Mpc/h of the Milky Way. Our analysis relies on constrained realization simulations and forward modelling of the 2M++ galaxy catalogue. We find that the angular distribution of neutrinos is anti-correlated with the projected matter density, due to the capture and deflection of neutrinos by massive structures along the line of sight. Of relevance to tritium capture experiments, we find that the gravitational clustering effect of the large-scale structure on the local number density of neutrinos is more important than that of the Milky Way for neutrino masses less than 0.1 eV. Nevertheless, we predict that the density of relic neutrinos is close to the cosmic average, with a suppression or enhancement over the mean of (-0.3%, +7%, +27%) for masses of (0.01, 0.05, 0.1) eV. This implies no more than a marginal increase in the event rate for tritium capture experiments like PTOLEMY. We also predict that the CNB and CMB rest frames coincide for 0.01 eV neutrinos, but that neutrino velocities are significantly perturbed for masses larger than 0.05 eV. Regardless of mass, we find that the angle between the neutrino dipole and the ecliptic plane is small, implying a near-maximal annual modulation in the bulk velocity. Along with this paper, we publicly release our simulation data, comprising more than 100 simulations for six different neutrino masses.

The active galaxy NGC 1068 was recently identified by the IceCube neutrino observatory as the first known steady-state, extragalactic neutrino point source, associated with about 79 events over ten years. We use the IceCube data to place limits on possible neutrino self-interactions mediated by scalar particles with mass between 1 - 10 MeV. We find that constraints on flavor-specific $ν_τ$ self-interactions with low mediator masses are comparable to constraints derived from the diffuse high-energy neutrino flux at low energies, while constraints on flavor-universal self-interactions are less restrictive than current bounds.

We develop a first-principles formalism to compute the distortion to the relic neutrino density field caused by the peculiar motions of large-scale structures. This distortion slows halos down due to dynamical friction, causes a local anisotropy in the neutrino-CDM cross-correlation, and reduces the global cross-correlation between neutrinos and CDM. The local anisotropy in the neutrino-CDM cross-spectrum is imprinted in the three point cross-correlations of matter and galaxies, or the bispectrum in Fourier space, producing a signal peaking at squeezed triangle configurations. This bispectrum signature of neutrino masses is not limited by cosmic variance or potential inaccuracies in the modeling of complicated nonlinear and galaxy formation physics, and it is not degenerate with the optical depth to reionization. We show that future surveys have the potential to detect the distortion bispectrum.

The IceCube Neutrino Observatory has recently reported strong evidence for neutrino emission from the Galactic plane. The signal is consistent with model predictions of diffuse emission from cosmic ray propagation in the interstellar medium. However, due to IceCube's limited potential of identifying individual neutrino sources, it is also feasible that unresolved Galactic sources could contribute to the observation. We investigate the contribution of this quasi-diffuse emission and show that the observed Galactic diffuse flux at 100~TeV could be dominated by hard emission of unresolved sources. Particularly interesting candidate sources are young massive stellar clusters that have been considered as cosmic-ray PeVatrons. We examine whether this hypothesis can be tested by the upcoming KM3NeT detector or the planned future facility IceCube-Gen2 with about five times the sensitivity of IceCube.

The Galactic diffuse emission (GDE) is formed when cosmic rays leave the sources where they were accelerated, diffusively propagate in the Galactic magnetic field, and interact with the interstellar medium and interstellar radiation field. GDE in $\gamma$-ray (GDE-$\gamma$) has been observed up to sub-PeV energies, though its origin may be explained by either cosmic-ray nuclei or electrons. We show that the $\gamma$-rays accompanying the high-energy neutrinos recently observed by the IceCube Observatory from the Galactic plane have a flux that is consistent with the GDE-$\gamma$ observed by the Fermi-LAT and Tibet AS$\gamma$ experiments around 1 TeV and 0.5 PeV, respectively. The consistency suggests that the diffuse $\gamma$-ray emission above $\sim$1 TeV could be dominated by hadronuclear interactions, though partial leptonic contribution cannot be excluded. Moreover, by comparing the fluxes of the Galactic and extragalactic diffuse emission backgrounds, we find that the neutrino luminosity of the Milky Way is one to two orders of magnitude lower than the average of distant galaxies. This implies that our Galaxy has not hosted the type of neutrino emitters that dominates the isotropic neutrino background in the past few million years.

The probabilities of $ν^{}_μ \to ν^{}_{e}$ and $\overlineν^{}_μ \to \overlineν^{}_{e}$ oscillations in vacuum are determined by the CP-conserving flavor mixing factors ${\cal R}^{}_{ij} \equiv {\rm Re} (U^{}_{μi} U^{}_{e j} U^{*}_{μj} U^{*}_{e i})$ and the universal Jarlskog invariant of CP violation ${\cal J}^{}_ν \equiv (-1)^{i+j} \; {\rm Im} (U^{}_{μi} U^{}_{e j} U^{*}_{μj} U^{*}_{e i})$ (for $i, j = 1, 2, 3$ and $i < j$), where $U$ is the $3\times 3$ Pontecorvo-Maki-Nakagawa-Sakata neutrino mixing matrix. We show that ${\cal J}^{2}_ν = {\cal R}^{}_{12} {\cal R}^{}_{13} + {\cal R}^{}_{12} {\cal R}^{}_{23} + {\cal R}^{}_{13} {\cal R}^{}_{23}$ holds as a natural consequence of the unitarity of $U$. This Pythagoras-like relation may provide a novel cross-check of the result of ${\cal J}^{}_ν$ that will be directly measured in the next-generation long-baseline neutrino oscillation experiments. Indirect non-unitarity effects and terrestrial matter effects on ${\cal J}^{}_ν$ and ${\cal R}^{}_{ij}$ are also discussed.

We derive constraints on the couplings of light vector particles to all first-generation Standard Model fermions using leptonic decays of the charged pion, $π^+\to e^+ ν_e X_μ$. In models where the net charge to which $X_μ$ couples is not conserved, no lepton helicity flip is required for the decay to happen, enhancing the decay rate by factors of ${O}(m_π^4/m_e^2m_X^2)$. A past search at the SINDRUM-I spectrometer severely constrains this possibility. In the context of the hypothesized $17$ MeV particle proposed to explain anomalous $^8$Be, $^4$He, and $^{12}$C nuclear transitions claimed by the ATOMKI experiment, this limit rules out vector-boson explanations and poses strong limits on axial-vector ones.

We consider quantum-decoherence effects in neutrino oscillation data. Working in the open quantum system framework we adopt a phenomenological approach that allows to parameterize the energy dependence of the decoherence effects. We consider several phenomenological models. We analyze data from the reactor experiments RENO, Daya Bay and KamLAND and from the accelerator experiments NOvA, MINOS/MINOS+ and T2K. We obtain updated constraints on the decoherence parameters quantifying the strength of damping effects, which can be as low as $Γ_{ij} \lesssim 8 \times 10^{-27}$ GeV at 90% confidence level in some cases. We also present sensitivities for the future facilities DUNE and JUNO.

New probes of neutrino mixing are needed to advance precision studies. One promising direction is via the detection of low-energy atmospheric neutrinos (below a few hundred MeV), to which a variety of near-term experiments will have much-improved sensitivity. Here we focus on probing these neutrinos through distinctive nuclear signatures of exclusive neutrino-carbon interactions -- those that lead to detectable nuclear-decay signals with low backgrounds -- in both neutral-current and charged-current channels. The neutral-current signature is a line at 15.11 MeV and the charged-current signatures are two- or three-fold coincidences with delayed decays. We calculate the prospects for identifying such events in the Jiangmen Underground Neutrino Observatory (JUNO), a large-scale liquid-scintillator detector. A five-year exposure would yield about 16 neutral-current events (all flavors) and about 16 charged-current events (mostly from $ν_e + \barν_e$, with some from $ν_μ+ \barν_μ$), and thus roughly 25\% uncertainties on each of their rates. Our results show the potential of JUNO to make the first identified measurement of sub-100 MeV atmospheric neutrinos. They also are a step towards multi-detector studies of low-energy atmospheric neutrinos, with the goal of identifying additional distinctive nuclear signatures for carbon and other targets.

The general anomaly-free $U(1)'$ models allow non-universal lepton charges. We explore the sensitivities of FASER/FASER2, COHERENT and DUNE/T2HK precision experiments to the new gauge boson $Z'$ and the new CP-even scalar $φ$. With non-universal lepton charges, distinctive reaches at FASER/FASER2 emerge in the regime of low $m_{Z'}$ and small gauge coupling $g_{BL}$ for different $U(1)'$ charge setups. The COHERENT experiment and the future long-baseline experiments DUNE/T2HK also provide complementary probes to the available parameter space. For $m_φ< 2m_{Z'}$, the search for the scalar $φ$ at FASER/FASER2 is sensitive to the mixing angle between the scalar singlet and the SM Higgs. In the case of $m_φ> 2m_{Z'}$, the kinematically allowed decay $φ\to Z' Z'$ changes the lifetime and decay rates of the scalar $φ$. The sensitivity reach highly depends on the $Z'$ mass and the gauge coupling $g_{BL}$.

Gallium radioactive source experiments have reported a neutrino-induced event rate about 20\% lower than expected with a high statistical significance. We present an explanation of this observation assuming quantum decoherence of the neutrinos in the gallium detectors at a scale of 2~m. This explanation is consistent with global data on neutrino oscillations, including solar neutrinos, if decoherence effects decrease quickly with energy, for instance with a power law $E_\nu^{-r}$ with $r\simeq 12$. Our proposal does not require the presence of sterile neutrinos but implies a modification of the standard quantum mechanical evolution equations for active neutrinos.

The next Milky Way supernova will be an epochal event in multi-messenger astronomy, critical to tests of supernovae, neutrinos, and new physics. Realizing this potential depends on having realistic simulations of core collapse. We investigate the neutrino predictions of nearly all modern models (1-, 2-, and 3-d) over the first $\simeq$1 s, making the first detailed comparisons of these models to each other and to the SN 1987A neutrino data. Even with different methods and inputs, the models generally agree with each other. However, even considering the low neutrino counts, the models generally disagree with data. What can cause this? We show that neither neutrino oscillations nor different progenitor masses appear to be a sufficient solution. We outline urgently needed work.

Determination of neutrino mass ordering and precision measurement of neutrino oscillation parameters are the foremost goals of the JUNO experiment. Here, we explore the capability of JUNO experiment to constrain the scalar non-standard interactions (sNSI). sNSI appears as a correction to the neutrino mass term in the Hamiltonian. Our results show that JUNO can put very stringent constraints on sNSI, particularly for the case of inverted mass ordering. We also check JUNO's capability to determine mass ordering in the presence of sNSI and conclude that the possibility to confuse normal (inverted) mass ordering in the standard scenario (when there is no sNSI) with inverted (normal) ordering in the presence of sNSI exists only at the $3\sigma$ confidence level and above. Finally, we also comment on the precision measurements of $\sin^2\theta_{12}$, $\Delta m^2_{21}$ and $\Delta m^2_{31}$ in the presence of sNSI. We find that the $1\sigma$-allowed uncertainty in each of these oscillation parameters depends on the choice of mass ordering, sNSI parameters, and lightest neutrino mass $\rm m_{lightest}$, wherein a deterioration from a few percent in the case of standard interactions to $\sim13\%$ in the case of sNSI is possible.

After being produced as electron neutrinos ($\nu_e$), solar neutrinos partially change their flavor to $\nu_{\mu}$ and $\nu_{\tau}$ en route to Earth. Although the flavor ratio of the $\nu_e$ flux to the total flux has been well measured, the $\nu_{\mu}:\nu_{\tau}$ composition has not yet been experimentally probed. In this work we show that the $\nu_{\mu}:\nu_{\tau}$ flavor ratio could be measured by utilizing flavor-dependent radiative corrections in the cross sections for $\nu_{\mu}$ and $\nu_{\tau}$ scattering. Moreover, since the transition probabilities of $\nu_e$ to $\nu_\mu$ and $\nu_\tau$ depend on the leptonic CP phase, we also demonstrate that the method proposed in this work will allow next-generation neutrino experiments to probe leptonic CP violation through the observation of solar neutrinos.

With the help of a block parametrization of the canonical seesaw flavor textures in terms of the Euler-like rotation angles and CP-violaing phases, we derive a general and explicit expression for the Jarlskog invariant of CP violation in neutrino oscillations and compare it with the CP-violating asymmetries of heavy Majorana neutrino decays within the minimal seesaw framework which contains two right-handed neutrino fields. Two simplified scenarios are discussed to illustrate how direct or indirect the correlation between these two types of CP violation can be.

We present an updated and improved global fit analysis of current flavor and electroweak precision observables to derive bounds on unitarity deviations of the leptonic mixing matrix and on the mixing of heavy neutrinos with the active flavours. This new analysis is motivated by new and updated experimental results on key observables such as $V_{ud}$, the invisible decay width of the $Z$ boson and the $W$ boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistic, which may present significant deviations from a $\chi^2$ distribution. The results are provided for three different Type-I seesaw scenarios: the minimal scenario with only two additional right-handed neutrinos, the next to minimal one with three extra neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrize via a generic deviation from a unitary leptonic mixing matrix. Additionally, we also analyze the case of generic deviations from unitarity of the leptonic mixing matrix, not necessarily induced by the presence of additional neutrinos. This last case relaxes some correlations among the parameters and is able to provide a better fit to the data. Nevertheless, inducing only leptonic unitarity deviations avoiding both the correlations implied by the right-handed neutrino extension as well as more strongly constrained operators is challenging and would imply significantly more complex UV completions.

We examine solar neutrinos in dark matter detectors including the effects of flavor-dependent radiative corrections to the CE$\nu$NS cross section. Working within a full three-flavor framework, and including matter effects within the Sun and Earth, detectors with thresholds $\lesssim 1$ keV and exposures of $\sim 100$ ton-year could identify contributions to the cross section beyond tree level. The differences between the cross sections for the flavors, combined with the difference in fluxes, would provide a new and unique method to study the muon and tau components of the solar neutrino flux. Flavor-dependent corrections induce a small day-night asymmetry of $< |3 \times10^{-4}|$ in the event rate, which if ultimately accessible would provide a novel probe of flavor oscillations.

Very recently, HAWC observatory discovered the high-energy gamma ray emission from the solar disk during the quiescent stage of the sun, extending the Fermi-LAT detection of intense, hard emission between 0.1 - 200 GeV to TeV energies. The flux of these observed gamma-rays is significantly higher than that theoretically expected from hadronic interactions of galactic cosmic rays with the solar atmosphere. More importantly, spectral slope of Fermi and HAWC observed gamma ray energy spectra differ significantly from that of galactic cosmic rays casting doubt on the prevailing galactic cosmic ray ancestry model of solar disk gamma rays. In this letter, we argue that the quiet sun can accelerate cosmic rays to TeV energies with an appropriate flux level in the solar chromosphere, as the solar chromosphere in its quiet state probably possesses the required characteristics to accelerate cosmic rays to TeV energies. Consequently, the mystery of the origin of observed gamma rays from the solar disc can be resolved consistently through the hadronic interaction of these cosmic rays with solar matter above the photosphere in a quiet state. The upcoming IceCube-Gen2 detector should be able to validate the proposed model in future through observation of TeV muon neutrino flux from the solar disk. The proposed idea should have major implications on the origin of galactic cosmic rays.

Some properties of a neutrino may differ significantly depending on whether it is Dirac or Majorana type. The type is determined by the relative size of Dirac and Majorana masses, which may vary if they arise from an oscillating scalar dark matter. We show that the change can be significant enough to convert the neutrino type between Dirac and Majorana periodically while satisfying constraints on the dark matter. This neutrino type oscillation predicts periodic modulations in the event rates in various neutrino phenomena including the neutrinoless double beta decay. As the energy density and, thus, the oscillation amplitude of the dark matter evolves in the cosmic time scale, the neutrino masses change accordingly, which provides an interesting link between the present-time neutrino physics to the early universe cosmology including the leptogenesis.

An important goal of current and future long baseline neutrino oscillation experiments pertains to determination of the Dirac-type leptonic $CP$ phase, $\delta_{13}$. We consider the new physics scenario of an eV scale sterile neutrino along with three active neutrinos and demonstrate the impact on the $CP$ and $T$ violation measurements in neutrino oscillations. We address the question of disentangling the intrinsic effects from extrinsic effects in the standard three neutrino paradigm as well as the scenario with added light sterile neutrino. We define a metric to isolate the two kinds of effects and our approach is general in the sense that it is independent of the choice of $\delta_{13}$. We study the role of different appearance and disappearance channels which can contribute to CP and T violation measurements. We perform the analysis for different long baseline experiments which have different detection capabilities such as Water Cherenkov (WC) and Liquid Argon Time Projection Chamber (LArTPC).

Future long-baseline experiments will play an important role in exploring physics beyond the standard model. One such new physics concept is the large extra dimension (LED), which provides an elegant solution to the hierarchy problem. This model also explains the small neutrino mass in a natural way. The presence of LED modifies the standard neutrino oscillation probabilities. Hence, the long-baseline experiments are sensitive to the LED parameters. We explore the potential of the three future long-baseline neutrino experiments, namely T2HK, ESSnuSB, and DUNE, to probe the LED parameter space. We also compare the capability of the charged and neutral current measurements at DUNE to constrain the LED model. We find that T2HK will provide more stringent bounds on the largest compactification radius ($R_{\rm{ED}}$) compared to the DUNE and ESSnuSB experiments. At $90\%$ C.L., T2HK can exclude $R_{\rm{ED}}\sim 0.45~(0.425)$ $\mu$m for the normal (inverted) mass hierarchy scenario.

Neutrino-electron scattering experiments play a crucial role in investigating the non-standard interactions of neutrinos. In certain models, these interactions can include interference terms that may affect measurements. Next-generation direct detection experiments, designed primarily for dark-matter searches, are also getting sensitive to probe the neutrino properties. We utilise the data from XENONnT, a direct detection experiment, and Borexino, a low-energy solar neutrino experiment, to investigate the impact of interference on non-standard interactions. Our study considers models with an additional $U(1)$, including $U(1)_{B-L}$, $U(1)_{L_e-L_\mu}$, and $U(1)_{L_e-L_\tau}$, to investigate the impact of interference on non-standard neutrino interactions. We demonstrate that this interference can lead to a transition between the considered non-standard interaction models in the energy range relevant to both the XENONnT and Borexino experiments. This transition can be used to distinguish among the considered models if any signals are observed at direct detection or neutrino experiments. Our findings underscore the importance of accounting for the interference and incorporating both direct detection and solar neutrino experiments to gain a better understanding of neutrino interactions and properties.

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and non-standard interactions can violate this symmetry. In this work we report the measurements of $\sin^{2} \theta_{23}$ and $\Delta m_{32}^2$ independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of 1.97$\times$10$^{21}$ and 1.63$\times$10$^{21}$ protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross-section models, new near detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.

Our study aims to investigate the viability of neutrino mass models that arise from discrete non-Abelian modular symmetry groups, i.e., $\Gamma_N$ with ($N=1,2,3,\dots$) in the future neutrino experiments T2HK, DUNE, and JUNO. Modular symmetry reduces the usage of flavon fields compared to the conventional discrete flavor symmetry models. Theories based on modular symmetries predict the values of leptonic mixing parameters, and therefore, these models can be tested in future neutrino experiments. In this study, we consider three models based on the $A_4$ modular symmetry, i.e., Model-A, B, and C such a way that they predict different values of the oscillation parameters but still allowed with respect to the current data. In the future, it is expected that T2HK, DUNE, and JUNO will measure the neutrino oscillation parameters very precisely, and therefore, some of these models can be excluded in the future by these experiments. We have estimated the prediction of these models numerically and then used them as input to scrutinize these models in the neutrino experiments. Assuming the future best-fit values of $\theta_{23}$ and $\delta_{\rm CP}$ remain the same as the current one, our results show that at $5 \sigma$ C.L, Model-A can be excluded by T2HK whereas Model-B can be excluded by both T2HK and DUNE. Model-C cannot be excluded by T2HK and DUNE at $5 \sigma$ C.L. Further; our results show that JUNO alone can exclude Model-B at an extremely high confidence level if the future best-fit of $\theta_{12}$ remains at the current-one. We have also identified the region in the $\theta_{23}$ - $\delta_{\rm CP}$ parameter space, for which Model-A cannot be separated from Model-B in T2HK and DUNE.

We present a scalar-driven sterile neutrino production model where the interaction with the ultralight scalar field modifies the oscillation production of sterile neutrinos in the early universe. The model effectively suppresses the production of sterile neutrinos at low temperatures due to the heavy scalar mass, resulting in a colder matter power spectrum that avoids constraints from small-scale structure observations. In this model, the dominant dark matter relic is from sterile neutrinos, with only a small fraction originating from the ultralight scalar. Furthermore, the model predicts a detectable X/Gamma-ray flux proportional to the cubic density of local sterile neutrinos for a light scalar mass due to the light scalar coupling tosterile neutrinos. This distinguishes our model from normal decaying dark matter, which has a linear dependence on the density. In addition, the model predicts a potential low-energy monochromatic neutrino signal that can be detectable by future neutrino telescopes.

We derive new constraints on effective four-fermion neutrino non-standard interactions with both quarks and electrons. This is done through the global analysis of neutrino oscillation data and measurements of coherent elastic neutrino-nucleus scattering (CEvNS) obtained with different nuclei. In doing so, we include not only the effects of new physics on neutrino propagation but also on the detection cross section in neutrino experiments which are sensitive to the new physics. We consider both vector and axial-vector neutral-current neutrino interactions and, for each case, we include simultaneously all allowed effective operators in flavour space. To this end, we use the most general parametrization for their Wilson coefficients under the assumption that their neutrino flavour structure is independent of the charged fermion participating in the interaction. The status of the LMA-D solution is assessed for the first time in the case of new interactions taking place simultaneously with up quarks, down quarks, and electrons. One of the main results of our work are the presently allowed regions for the effective combinations of non-standard neutrino couplings, relevant for long-baseline and atmospheric neutrino oscillation experiments.

Identifying the Milky Way's very high energy hadronic cosmic-ray accelerators -- the PeVatrons -- is a critical problem. While gamma-ray observations reveal promising candidate sources, neutrino detection is needed for certainty, and this has not yet been successful. Why not? There are several possibilities, as we delineated in a recent paper [T. Sudoh and J. F. Beacom, Phys. Rev. D 107, 043002 (2023)]. Here we further explore the possibility that the challenges arise because PeVatrons have a large angular extent, either due to cosmic-ray propagation effects or due to clusters of sources. We show that while extended neutrino sources could be missed in the commonly used muon-track channel, they could be discovered in the all-flavor shower channel, which has a lower atmospheric-neutrino background flux per solid angle. Intrinsically, showers are quite directional and would appear so in water-based detectors like the future KM3NeT, even though they are presently badly smeared by light scattering in ice-based detectors like IceCube. Our results motivate new shower-based searches as part of the comprehensive approach to identifying the Milky Way's hadronic PeVatrons.

Dark matter particles can form halos gravitationally bound to massive astrophysical objects. The Earth could have such a halo where depending on the particle mass, the halo either extends beyond the surface or is confined to the Earth's interior. We consider the possibility that if dark matter particles are coupled to neutrinos, then neutrino oscillations can be used to probe the Earth's dark matter halo. In particular, atmospheric neutrinos traversing the Earth can be sensitive to a small size, interior halo, inaccessible by other means. Depending on the halo mass and neutrino energy, constraints on the dark matter-neutrino couplings are obtained from the halo corrections to the neutrino oscillations.

In this paper we place new bounds on CPT violation in the solar neutrino sector analyzing the results from solar experiments and KamLAND. We also discuss the sensitivity of the next-generation experiments DUNE and Hyper-Kamiokande, which will provide accurate measurements of the solar neutrino oscillation parameters. The joint analysis of both experiments will further improve the precision due to cancellations in the systematic uncertainties regarding the solar neutrino flux. In combination with the next-generation reactor experiment JUNO, the bound on CPT violation in the solar sector could be improved by one order of magnitude in comparison with current constraints. The distinguishability among CPT-violating neutrino oscillations and neutrino non-standard interactions in the solar sector is also addressed.

Discovering new neutrino interactions would represent evidence of physics beyond the Standard Model. We focus on new flavor-dependent long-range neutrino interactions mediated by ultra-light mediators, with masses below $10^{-10}$ eV, introduced by new lepton-number gauge symmetries $L_e-L_\mu$, $L_e-L_\tau$, and $L_\mu-L_\tau$. Because the interaction range is ultra-long, nearby and distant matter - primarily electrons and neutrons - in the Earth, Moon, Sun, Milky Way, and the local Universe, may source a large matter potential that modifies neutrino oscillation probabilities. The upcoming Deep Underground Neutrino Experiment (DUNE) and the Tokai-to-Hyper-Kamiokande (T2HK) long-baseline neutrino experiments will provide an opportunity to search for these interactions, thanks to their high event rates and well-characterized neutrino beams. We forecast their probing power. Our results reveal novel perspectives. Alone, DUNE and T2HK may strongly constrain long-range interactions, setting new limits on their coupling strength for mediators lighter than $10^{-18}$ eV. However, if the new interactions are subdominant, then both DUNE and T2HK, together, will be needed to discover them, since their combination lifts parameter degeneracies that weaken their individual sensitivity. DUNE and T2HK, especially when combined, provide a valuable opportunity to explore physics beyond the Standard Model.

The elastic scattering between dark matter (DM) and radiation can potentially explain small-scale observations that the cold dark matter faces as a challenge, as damping density fluctuations via dark acoustic oscillations in the early universe erases small-scale structure. We study a semi-analytical subhalo model for interacting dark matter with radiation, based on the extended Press-Schechter formalism and subhalos' tidal evolution prescription. We also test the elastic scattering between DM and neutrinos using observations of Milky-Way satellites from the Dark Energy Survey and PanSTARRS1. We conservatively impose strong constraints on the DM-neutrino scattering cross section of $\sigma_{{\rm DM}\text{-}\nu,n}\propto E_\nu^n$ $(n=0,2,4)$ at $95\%$ confidence level (CL), $\sigma_{{\rm DM}\text{-}\nu,0}< 10^{-32}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})$, $\sigma_{{\rm DM}\text{-}\nu,2}< 10^{-43}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})(E_\nu/E_{\nu}^0)^2$ and $\sigma_{{\rm DM}\text{-}\nu,4}< 10^{-54}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})(E_\nu/E_{\nu}^0)^4$, where $E_\nu^0$ is the average momentum of relic cosmic neutrinos today, $E_\nu^0 \simeq 3.15 T_\nu^0 \simeq 6.1\ {\rm K}$. By imposing a satellite forming condition, we obtain the strongest upper bounds on the DM-neutrino cross section at $95\%$ CL, $\sigma_{{\rm DM}\text{-}\nu,0}< 4\times 10^{-34}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})$, $\sigma_{{\rm DM}\text{-}\nu,2}< 10^{-46}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})(E_\nu/E_{\nu}^0)^2$ and $\sigma_{{\rm DM}\text{-}\nu,4}< 7\times 10^{-59}\ {\rm cm^2}\ (m_{\rm DM}/{\rm GeV})(E_\nu/E_{\nu}^0)^4$.

The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos prior to recombination. The CMB is a particularly powerful probe of new eV-scale bosons interacting with neutrinos, as these particles can thermalize with neutrinos via the inverse decay process, $\nu\bar{\nu} \rightarrow X$, and suppress neutrino free streaming near recombination -- even for couplings as small as $\lambda_\nu \sim \mathcal{O}(10^{-13})$. Here, we revisit CMB constraints on such bosons, improving upon a number of approximations previously adopted in the literature and generalizing the constraints to a broader class of models. This includes scenarios in which the boson is either spin-$0$ or spin-$1$, the number of interacting neutrinos is either $N_{\rm int} = 1,2 $ or $3$, and the case in which a primordial abundance of the species is present. We apply these bounds to well-motivated models, such as the singlet majoron model or a light $U(1)_{L_\mu-L_\tau}$ gauge boson, and find that they represent the leading constraints for masses $m_X\sim 1\, {\rm eV}$. Finally, we revisit the extent to which neutrino-philic bosons can ameliorate the Hubble tension, and find that recent improvements in the understanding of how such bosons damp neutrino free streaming reduces the previously found success of this proposal.

We explore an extension of the standard $\Lambda$CDM model by including an interaction between neutrinos and dark matter, and making use of the ground based telescope data of the Cosmic Microwave Background (CMB) from the Atacama Cosmology Telescope (ACT). An indication for a non-zero coupling between dark matter and neutrinos (both assuming a temperature independent and $T^2$ dependent cross-section) is obtained at the 1$\sigma$ level coming from the ACT CMB data alone and when combined with the Planck CMB and Baryon Acoustic Oscillations (BAO) measurements. This result is confirmed by both fixing the effective number of relativistic degrees of freedom in the early Universe to the Standard Model value of $N_{\rm eff}=3.044$, and allowing $N_{\rm eff}$ to be a free cosmological parameter. Furthermore, when performing a Bayesian model comparison, the interacting $\nu$DM (+$N_{\rm eff}$) scenario is mostly preferred over a baseline $\Lambda$CDM (+$N_{\rm eff}$) cosmology. The preferred value is then used as a benchmark and the potential implications of dark matter's interaction with a sterile neutrino are discussed.

We describe a new data sample of IceCube DeepCore and report on the latest measurement of atmospheric neutrino oscillations obtained with data recorded between 2011-2019. The sample includes significant improvements in data calibration, detector simulation, and data processing, and the analysis benefits from a detailed treatment of systematic uncertainties, with significantly higher level of detail since our last study. By measuring the relative fluxes of neutrino flavors as a function of their reconstructed energies and arrival directions we constrain the atmospheric neutrino mixing parameters to be $\sin^2θ_{23} = 0.51\pm 0.05$ and $Δm^2_{32} = 2.41\pm0.07\times 10^{-3}\mathrm{eV}^2$, assuming a normal mass ordering. The resulting 40\% reduction in the error of both parameters with respect to our previous result makes this the most precise measurement of oscillation parameters using atmospheric neutrinos. Our results are also compatible and complementary to those obtained using neutrino beams from accelerators, which are obtained at lower neutrino energies and are subject to different sources of uncertainties.

Recent data from the ATOMKI group continues to confirm their claim of the existence of a new $\sim17$ MeV particle. We review and numerically analyze the data and then put into context constraints from other experiments, notably neutrino scattering experiments such as the latest reactor anti-neutrino coherent elastic neutrino nucleus scattering data and unitarity constraints from solar neutrino observations. We show that minimal scenarios are disfavored and discuss the model requirements to evade these constraints.

Recently, the IceCube collaboration observed a neutrino excess in the direction of NGC 1068 with high statistical significance. This constitutes the second detection of an astrophysical neutrino point source after the discovery of a variable emission originating from the blazar TXS~0506+056. Neutrinos emitted by these sources traverse huge, well-determined distances on their way to Earth. This makes them a promising tool to test new physics in the neutrino sector. We consider secret interactions with the cosmic neutrino background and discuss their impact on the flux of neutrino point sources. The observation of emission from NGC 1068 and TXS 0506+056 can then be used to put limits on the strength of the interaction. We find that our ignorance of the absolute neutrino masses has a strong impact and, therefore, we present limits in two benchmark scenarios with the sum of the neutrino masses around their lower and upper limits.

The precise determination of the leptonic CP phase is one of the major goals for future generation Long Baseline experiments. On the other hand, if new physics beyond the Standard Model exists, a robust determination of such a CP phase may be a challenge. Moreover, it has been pointed out that, in this scenario, an apparent discrepancy in the CP phase measurement at different experiments may arise. In this work, we investigate the robustness of the determination of the Dirac CP-phase at several long-baseline configurations: ESSnuSB, T2HKK, and a DUNE-like experiment. We use the non-standard neutrino interactions (NSI) formalism as a framework. We found that complementary between ESSnuSB and a DUNE-like experiment enhances the robustness in the determination of the CP-phase, even in the presence of matter NSI. Moreover, the T2HKK proposal can help to constrain the matter NSI parameters.

It remains a possibility that neutrinos are pseudo-Dirac states, such that a generation is composed of two maximally mixed Majorana neutrinos separated by a very small mass difference. We explore the physics potential of the JUNO experiment in constraining this possibility using the measurement of solar neutrinos. In particular, we investigate cases where one or three sterile states are present in addition to the active states. We consider two scenarios: one where JUNO's energy threshold allows for the measurement of $pp$ solar neutrinos, and the case where JUNO can only measure $^7$Be neutrinos and above. We find that JUNO will be able to constrain pseudo-Dirac mass splittings of $\delta m^2 \gtrsim 2.9\times 10^{-13}~{\rm eV^2}$ for the scenario including $pp$ solar neutrinos, and $\delta m^2 \gtrsim 1.9\times 10^{-12}~{\rm eV^2}$ when the measurement only considers $^7$Be monochromatic neutrinos, at the $3\sigma$ C.L. Thus, including $pp$ neutrinos will be crucial for JUNO to improve current constraints on the pseudo-Dirac scenario from solar neutrinos.

The seesaw mechanism with three right-handed neutrinos has one as a well-motivated dark matter candidate if stable and the other two can explain baryon asymmetry via the thermal leptogenesis scenario. We explore the possibility of introducing additional particles to make the right-handed neutrino dark matter in thermal equilibrium and freeze out through a forbidden annihilation channel. Nowadays in the Universe, this forbidden channel can be reactivated by a strong gravitational potential such as the supermassive black hole in our galaxy center. The Fermi-LAT gamma ray data and dark matter relic density require this right-handed neutrino dark matter to have mass below $100\,$GeV and the existence of an additional boson $\phi$ that can be tested at future lepton colliders.

There are several unanswered questions regarding neutrinos which pave the way for physics beyond the standard model (SM) of particle physics. Generalized interactions of neutrinos provide a way to characterize these effects in a manner which is even more general than the oft-studied non-standard neutrino interactions. These interactions are described by higher dimensional operators maintaining the SM gauge symmetries. On the other hand cosmic neutrino background, although yet to be detected directly, is a robust prediction of the SM and the standard cosmology. We perform a global analysis of the relevant generalized neutrino interactions which are expressly relevant for the proposed cosmic neutrino detector PTOLEMY. The electron spectrum due to the capture of cosmic neutrinos on radioactive tritium gets modified due to the presence of these generalized interactions. We also show how the differential electron spectrum is sensitive to the finite experimental resolution, mass of the lightest neutrino eigenstate, the strength of these interactions and the ordering of neutrino mass.

We point out a new mechanism giving rise to anomalous tau neutrino appearance at the near detectors of beam-focused neutrino experiments, without extending the neutrino sector. The charged mesons ($\pi^\pm, K^\pm$) produced and focused in the target-horn system can decay to a (neutrino-philic) light mediator via the helicity-unsuppressed three-body decays. If such a mediator carries non-vanishing hadronic couplings, it can also be produced via the bremsstrahlung of the incident proton beam. The subsequent decay of the mediator to a tau neutrino pair results in tau neutrino detection at the near detectors, which is unexpected under the standard three-flavor neutrino oscillation paradigm. We argue that the signal flux from the charged meson decays can be significant enough to discover the light mediator signal at the on-axis liquid-argon near detector of the DUNE experiment, due to the focusing of charged mesons. In addition, we show that ICARUS-NuMI, an off-axis near detector of the NuMI beam, as well as DUNE, can observe a handful of tau neutrino events induced by beam-proton bremsstrahlung.

Recently the neutrino experiments ANTARES and IceCube have released new constraints to the non-standard neutrino interaction (NSI) parameter $\epsilon^d_{\mu\tau}$ (flavor off-diagonal). These new constraints are stronger than those obtained from a combination of COHERENT and neutrino oscillation data. In the light of the recent constraints from ANTARES and IceCube data on the NSI parameter $\epsilon^d_{\mu\tau}$, in this work, we study the new physics implications on the parameter space of a simplified $Z^\prime$ model with lepton flavor violating ($\mu\tau$) couplings. For a $Z^\prime$ boson with a mass heavier than the $\tau$ lepton, our results show that ANTARES and IceCube put strong constraints to such a new physics scenario with $\mu\tau$ couplings. In addition, these neutrino experiments can exclude a similar region than ATLAS experiment, showing the potential to provide complementary information to the one obtained from direct searches at the Large Hadron Collider. The impact of the expected sensitivity reach on $\epsilon^d_{\mu\tau}$ at DUNE experiment is also studied.

We present a catalog of likely astrophysical neutrino track-like events from the IceCube Neutrino Observatory. IceCube began reporting likely astrophysical neutrinos in 2016 and this system was updated in 2019. The catalog presented here includes events that were reported in real-time since 2019, as well as events identified in archival data samples starting from 2011. We report 275 neutrino events from two selection channels as the first entries in the catalog, the IceCube Event Catalog of Alert Tracks, which will see ongoing extensions with additional alerts. The gold and bronze alert channels respectively provide neutrino candidates with 50\% and 30\% probability of being astrophysical, on average assuming an astrophysical neutrino power law energy spectral index of 2.19. For each neutrino alert, we provide the reconstructed energy, direction, false alarm rate, probability of being astrophysical in origin, and likelihood contours describing the spatial uncertainty in the alert's reconstructed location. We also investigate a directional correlation of these neutrino events with gamma-ray and X-ray catalogs including 4FGL, 3HWC, TeVCat and Swift-BAT.

A hermitian matrix can be parametrized by a set consisting of its determinant and the eigenvalues of its submatrices. We established a group of equations which connect these variables with the mixing parameters of diagonalization. These equations are simple in structure and manifestly invariant in form under the symmetry operations of dilatation, translation, rephasing and permutation. When applied to the problem of neutrino oscillation in matter they produced two new ``matter invariants" which are confirmed by available data.

Antineutrinos from nuclear reactors can be used for monitoring in the mid- to far-field as part of a non-proliferation toolkit. Antineutrinos are an unshieldable signal and carry information about the reactor core and the distance they travel. Using gadolinium-doped water Cherenkov detectors for this purpose has been previously proposed alongside rate-only analyses. As antineutrinos carry information about their distance of travel in their energy spectrum, the analyses can be extended to a spectral analysis to gain more knowledge about the detected core. Two complementary analyses are used to evaluate the distance between a proposed gadolinium-doped water-based liquid scintillator detector and a detected nuclear reactor. Example cases are shown for a detector in Boulby Mine, near the Boulby Underground Laboratory in the UK, and six reactor sites in the UK and France. The analyses both show strong potential to range reactors, but are limited by the detector design.

We test for an anisotropy in the mass of arriving cosmic-ray primaries associated with the galactic plane. The sensitivity to primary mass is obtained through the depth of shower maximum, $X_{\rm max}$, extracted from hybrid events measured over a 14-year period at the Pierre Auger Observatory. The sky is split into distinct on- and off-plane regions using the galactic latitude of each arriving cosmic ray to form two distributions of $X_{\rm max}$, which are compared using an Anderson-Darling 2-samples test. A scan over roughly half of the data is used to select a lower threshold energy of $10^{18.7}\,$eV and a galactic latitude splitting at $|b| = 30^\circ$, which are set as a prescription for the remaining data. With these thresholds, the distribution of $X_{\rm max}$ from the on-plane region is found to have a $9.1 \pm 1.6^{+2.1}_{-2.2}\,$g$\,$cm$^-2$ shallower mean and a $5.9\pm2.1^{+3.5}_{-2.5}\,$g$\,$cm$^-2$ narrower width than that of the off-plane region and is observed in all telescope sites independently. These differences indicate that the mean mass of primary particles arriving from the on-plane region is greater than that of those from the off-plane region. Monte Carlo studies yield a $5.9\times10^{-6}$ random chance probability for the result in the independent data, lowering to a $6.0\times10^{-7}$ post-penalization random chance probability when the scanned data is included. Accounting for systematic uncertainties leads to an indication for anisotropy in mass composition above $10^{18.7}\,$eV with a $3.3\,\sigma$ significance. Furthermore, the result has been newly tested using additional FD data recovered from the selection process. This test independently disfavors the on- and off-plane regions being uniform in composition at the $2.2\,\sigma$ level, which is in good agreement with the expected sensitivity of the dataset used for this test.

We simulate the evolution of the helicity of relic neutrinos as they propagate to Earth through a realistic model of the Galactic magnetic field, improving upon the rough estimates in the pioneering work of Baym and Peng. We find that with magnetic moments consistent with experimental bounds and even several orders of magnitude smaller, the helicity of relic neutrinos rotates with a substantial directional anisotropy. Averaged over directions this would simply reduce the apparent flux; if the direction of the incident neutrino could be measured, the directional anisotropy in the interaction probability could become a powerful diagnostic. We study the effects of $\nu$ spin rotation on C$\nu$B detection through the inverse tritium decay process.

We present PEANUTS (Propagation and Evolution of Active NeUTrinoS), an open-source Python package for the automatic computation of solar neutrino spectra and active neutrino propagation through Earth. PEANUTS is designed to be fast, by employing analytic formulae for the neutrino propagation through varying matter density, and flexible, by allowing the user to input arbitrary solar models, custom Earth density profiles and general detector locations. It provides functionalities for a fully automated simulation of solar neutrino fluxes at a detector, as well as access to individual routines to perform more specialised computations. The software has been extensively tested against the results of the SNO experiment, providing excellent agreement with their results. In addition, the present text contains a pedagogical derivation of the relations needed to compute the oscillated solar neutrino spectra, neutrino propagation through Earth and nadir exposure of an experiment.

We adopt the quantum field theoretical method to calculate the amplitude and event rate for a neutrino oscillation experiment, considering neutrino production, propagation and detection as a single process. This method allows to take into account decoherence effects in the transition amplitude induced by the quantum mechanical uncertainties of all particles involved in the process. We extend the method to include coherence loss due to interactions with the environment, similar to collisional line broadening. In addition to generic decoherence induced at the amplitude level, the formalism allows to include, in a straightforward way, additional damping effects related to phase-space integrals over momenta of unobserved particles as well as other classical averaging effects. We apply this method to neutrino oscillation searches at reactor and Gallium experiments and confirm that quantum decoherence is many orders of magnitudes smaller than classical averaging effects and therefore unobservable. The method used here can be applied with minimal modifications also to other types of oscillation experiments, e.g., accelerator based beam experiments.

We report the first direct observation of neutrino interactions at a particle collider experiment. Neutrino candidate events are identified in a 13.6 TeV center-of-mass energy $pp$ collision data set of 35.4 fb${}^{-1}$ using the active electronic components of the FASER detector at the Large Hadron Collider. The candidates are required to have a track propagating through the entire length of the FASER detector and be consistent with a muon neutrino charged-current interaction. We infer $153^{+12}_{-13}$ neutrino interactions with a significance of 16 standard deviations above the background-only hypothesis. These events are consistent with the characteristics expected from neutrino interactions in terms of secondary particle production and spatial distribution, and they imply the observation of both neutrinos and anti-neutrinos with an incident neutrino energy of significantly above 200 GeV.

We infer the ultrahigh energy neutrino source by using the Glashow resonance candidate event recently identified by the IceCube Observatory. For the calculation of the cross section for the Glashow resonance, we incorporate both the atomic Doppler broadening effect and initial state radiation $\overline{\nu}^{}_{e} e^- \to W^- \gamma$, which correct the original cross section considerably. Using available experimental information, we have set a generic constraint on the $\overline{\nu}^{}_{e}$ fraction of astrophysical neutrinos, which excludes the $\mu$-damped ${\rm p}\gamma$ source around $2\sigma$ confidence level. While a weak preference has been found for the pp source, next-generation measurements will be able to distinguish between ideal pp and p$\gamma$ sources with a high significance assuming an optimistic single power-law neutrino spectrum.

In the recent Baksan Experiment on Sterile Transitions (BEST), a suppressed rate of neutrino absorption on a gallium target was observed, consistent with earlier results from neutrino source calibrations of the SAGE and GALLEX/GNO solar neutrino experiments. The BEST collaboration, utilizing a 3.4 MCi 51Cr neutrino source, found observed-to-expected counting rates at two very short baselines of R=0.791 plus/minus 0.05 and 0.766 plus/minus 0.05, respectively. Among recent neutrino experiments, BEST is notable for the simplicity of both its neutrino spectrum, line neutrinos from an electron-capture source whose intensity can be measured to a estimated precision of 0.23%, and its absorption cross section, where the precisely known rate of electron capture to the gallium ground state, 71Ge(e,nue)71Ga(g.s.), establishes a minimum value. However, the absorption cross section uncertainty is a common systematic in the BEST, SAGE, and GALLEX/GNO neutrino source experiments. Here we update that cross section, considering a variety of electroweak corrections and the role of transitions to excited states, to establish both a central value and reasonable uncertainty, thereby enabling a more accurate assessment of the statistical significance of the gallium anomalies. Results are given for 51Cr and 37Ar sources. The revised neutrino capture rates are used in a re-evaluation of the BEST and gallium anomalies.

We present a state-of-the-art prediction for cross sections of neutrino deeply inelastic scattering (DIS) from nucleon at high neutrino energies, $E_\nu$, from 100 GeV to 1000 EeV ($10^{12}$ GeV). Our calculations are based on the latest CT18 NNLO parton distribution functions (PDFs) and their associated uncertainties. In order to make predictions for the highest energies, we extrapolate the PDFs to small $x$ according to several procedures and assumptions, thus affecting the uncertainties at ultra-high $E_\nu$; we quantify the uncertainties corresponding to these choices. Similarly, we quantify the uncertainties introduced by the nuclear corrections which are required to evaluate neutrino-nuclear cross sections for neutrino telescopes. These results can be applied to currently-running astrophysical neutrino observatories, such as IceCube, as well as various future experiments which have been proposed.

Next-generation large-volume detectors, such as GRAND, POEMMA, Trinity, TAROGE-M, TAMBO, or PUEO, have been designed to search for ultra-high-energy cosmic rays (UHECRs) with unprecedented sensitivity. We propose to use these detectors to search for new physics beyond the Standard Model (BSM). By considering the simple case of a right-handed neutrino that mixes exclusively with the active $\tau$ neutrino, we demonstrate that the existence of new physics can increase the probability for UHECRs to propagate through the Earth and produce extensive air showers that will be measurable soon. We compare the fluxes of such showers that would arise from various diffuse and transient sources of high-energy neutrinos, both in the Standard Model and in the presence of a right-handed neutrino. We show that detecting events with emergence angles $\gtrsim 10$ deg is promising to probe the existence of BSM physics, and we study the sensitivity of GRAND and POEMMA to do so. In particular, we show that the hypothesis of a right-handed neutrino with a mass of $\mathcal O(1-16)$ GeV may be probed in the future for mixing angles as small as $|U_{\tau N}|^2 \gtrsim 10^{-7}$, thus competing with existing and projected experimental limits.

In various high-energy physics contexts, such as neutrino-oscillation experiments, several assumptions underlying the typical asymptotic confidence interval construction are violated, such that one has to resort to computationally expensive methods like the Feldman-Cousins method for obtaining confidence intervals with proper statistical coverage. By construction, the computation of intervals at high confidence levels requires fitting millions or billions of pseudo-experiments, while wasting most of the computational cost on overly precise intervals at low confidence levels. In this work, a simple importance sampling method is introduced which reuses pseudo-experiments produced for all tested parameter values in a single mixture distribution. This results in a significant error reduction on the estimated critical values, especially at high confidence levels, and simultaneously yields a correct interpolation of these critical values between the parameter values at which the pseudo-experiments were produced. The theoretically calculated performance is demonstrated numerically using a simple example from the analysis of neutrino oscillations. The relationship to similar techniques applied in statistical mechanics and $p$-value computations is discussed.

Nuclear matrix elements (NME) are a crucial input for the interpretation of neutrinoless double beta decay data. We consider a representative set of recent NME calculations from different methods and investigate the impact on the present bound on the effective Majorana mass $m_{\beta\beta}$ by performing a combined analysis of the available data as well as on the sensitivity reach of future projects. A crucial role is played by the recently discovered short-range contribution to the NME, induced by light Majorana neutrino masses. Depending on the NME model and the relative sign of the long- and short-range contributions, the current $3\sigma$ bound can change between $m_{\beta\beta} < 40$ meV and 600 meV. The sign-uncertainty may either boost the sensitivity of next-generation experiments beyond the region for $m_{\beta\beta}$ predicted for inverted mass ordering or prevent even advanced setups to reach this region. Furthermore, we study the possibility to distinguish between different NME calculations by assuming a positive signal and by combining measurements from different isotopes. Such a discrimination will be impossible if the relative sign of the long- and short-range contribution remains unknown, but can become feasible if $m_{\beta\beta} \gtrsim 40$ meV and if the relative sign is known to be positive. Sensitivities will be dominated by the advanced $^{76}$Ge and $^{136}$Xe setups assumed here, but NME model-discrimination improves if data from a third isotope is added, e.g., from $^{130}$Te or $^{100}$Mo.

(abridged) Ultra-high energy cosmic rays (UHECRs) are highly energetic charged particles with energies exceeding $10^{18}$ eV. Identifying their sources and production mechanism can provide insight into many open questions in astrophysics and high energy physics. However, the Galactic magnetic field (GMF) deflects UHECRs, and the high uncertainties in our current understanding of the $3$-dimensional structure of the GMF does not permit us to accurately determine their true arrival direction on the plane of the sky (PoS). This difficulty arises from the fact that currently all GMF observations are integrated along the line-of-sight (LoS). Upcoming stellar optopolarimetric surveys as well as Gaia data on stellar parallaxes, are expected to provide local measurements of the GMF in the near future. In this paper, we evaluate the reconstruction of the GMF in a limited region of the Galaxy given sparse and local GMF measurements within that region, through Bayesian inference using principles of Information Field Theory. We backtrack UHECRs through GMF configurations drawn from the posterior to improve our knowledge of their true arrival directions. We show that, for a weakly turbulent GMF, it is possible to correct for its effect on the observed arrival direction of UHECRs to within $\sim 3^\circ$. For completely turbulent fields, we show that our procedure can still be used to significantly improve our knowledge on the true arrival direction of UHECRs.

Earth neutrino tomography is a realistic possibility with current and future neutrino detectors, complementary to geophysics methods. The two main approaches are based on either partial absorption of the neutrino flux as it propagates through the Earth (at energies about a few TeV) or on coherent Earth matter effects affecting the neutrino oscillations pattern (at energies below a few tens of GeV). In this work, we consider the latter approach focusing on supernova neutrinos with tens of MeV. Whereas at GeV energies, Earth matter effects are driven by the atmospheric mass-squared difference, at energies below $\sim 100$~MeV, it is the solar mass-squared difference what controls them. Unlike solar neutrinos, which suffer from significant weakening of the contribution to the oscillatory effect from remote structures due to the neutrino energy reconstruction capabilities of detectors, supernova neutrinos can have higher energies and thus, can better probe the Earth's interior. We shall revisit this possibility, using the most recent neutrino oscillation parameters and up-to-date supernova neutrino spectra. The capabilities of future neutrino detectors, such as DUNE, Hyper-Kamiokande and JUNO are presented, including the impact of the energy resolution and other factors. Assuming a supernova burst at 10~kpc, we show that the average Earth's core density could be determined within $\lesssim 10\%$ at $1\sigma$ confidence level, being Hyper-Kamiokande, with its largest mass, the most promising detector to achieve this goal.

The COHERENT collaboration observed coherent elastic neutrino nucleus scattering using a 14.6 kg cesium-iodide (CsI) detector in 2017 and recently published the updated results before decommissioning the detector. Here, we present the legacy determination of the weak mixing angle and of the average neutron rms radius of $^{133}\mathrm{Cs}$ and $^{127}\mathrm{I}$ obtained with the full CsI dataset, also exploiting the combination with the atomic parity violation (APV) experimental result, that allows us to achieve a precision as low as $\sim$4.5% and to disentangle the contributions of the $^{133}\mathrm{Cs}$ and $^{127}\mathrm{I}$ nuclei. Interestingly, we show that the COHERENT CsI data show a 6$σ$ evidence of the nuclear structure suppression of the full coherence. Moreover, we derive a data-driven APV+COHERENT measurement of the low-energy weak mixing angle with a percent uncertainty, independent of the value of the average neutron rms radius of $^{133}\mathrm{Cs}$ and $^{127}\mathrm{I}$, that is allowed to vary freely in the fit. Additionally, we extensively discuss the impact of using two different determinations of the theoretical parity non-conserving amplitude in the APV fit. Our findings show that the particular choice can make a significant difference, up to 6.5% on $R_n$(Cs) and 11% on the weak mixing angle. Finally, in light of the recent announcement of a future deployment of a 10 kg and a $\sim$700 kg cryogenic CsI detectors, we provide future prospects for these measurements, comparing them with other competitive experiments that are foreseen in the near future.

The direction and magnitude of the dipole anisotropy of ultra-high-energy cosmic rays with energies above 8 EeV observed by the Pierre Auger Observatory indicate their extragalactic origin. The observed dipole on Earth does not necessarily need to correspond to the anisotropy of the extragalactic cosmic-ray flux due to the effects of propagation in the Galactic magnetic field. We estimate the size of these effects via numerical simulations using the CRPropa 3 package. The Jansson-Farrar and Terral-Ferri\`ere models of the Galactic magnetic field are used to propagate particles from the edge of the Galaxy to an observer on Earth. We identify allowed directions and amplitudes of the dipole outside the Galaxy that are compatible with the measured features of the dipole on Earth for various mass composition scenarios at the 68% and 95% confidence level.

We present the first fully differential predictions for tau neutrino scattering in the energy region relevant to the DUNE experiment, including all spin correlations and all tau lepton decay channels. The calculation is performed using a generic interface between the neutrino event generator Achilles and the publicly available, general-purpose collider event simulation framework Sherpa.

A series of experiments studying neutrinos from intense radioactive sources have reported a deficit in the measured event rate which, in combination, has reached a statistical significance of $\sim 5\sigma$. In this paper, we explore avenues for explaining this anomaly, both within the Standard Model and beyond. First, we discuss possible biases in the predicted cross section for the detection reaction $\nu_e + ^{71}\text{Ga} \to e^- + ^{71}\text{Ge}$, which could arise from mismeasurement of the inverse process, $^{71}\text{Ge}$ decay, or from the presence of as yet unknown low-lying excited states of $^{71}\text{Ga}$. The latter would imply that not all $^{71}\text{Ge}$ decays go to the ground state of $^{71}\text{Ga}$, so the extraction of the ground state-to-ground state matrix element relevant for neutrino capture on gallium would be incorrect. Second, we scrutinize the measurement of the source intensity in gallium experiments, and we point out that a $\sim 2\%$ error in the branching ratios for $^{51}\text{Cr}$ decay would be enough to explain the anomaly. Third, we investigate the calibration of the radiochemical germanium extraction efficiency as a possible origin of anomaly. Finally, we outline several new explanations beyond the Standard Model, including scenarios with sterile neutrinos coupled to fuzzy dark matter or to dark energy, as well as a model with decaying sterile neutrinos. We critically assess the viability of these scenarios, and others that have been proposed, in a summary table.

Atmospheric muon neutrinos are produced by meson decays in cosmic-ray-induced air showers. The flux depends on meteorological quantities such as the air temperature, which affects the density of air. Competition between decay and re-interaction of those mesons in the first particle production generations gives rise to a higher neutrino flux when the air density in the stratosphere is lower, corresponding to a higher temperature. A measurement of a temperature dependence of the atmospheric $\nu_{\mu}$ flux provides a novel method for constraining hadro\-nic interaction models of air showers. It is particularly sensitive to the production of kaons. Studying this temperature dependence for the first time requires a large sample of high-energy neutrinos as well as a detailed understanding of atmospheric properties. We report the significant ($> 10 \sigma$) observation of a correlation between the rate of more than 260,000 neutrinos, detected by IceCube between 2012 and 2018, and atmospheric temperatures of the stratosphere, measured by the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's AQUA satellite. For the observed 10$\%$ seasonal change of effective atmospheric temperature we measure a 3.5(3)$\%$ change in the muon neutrino flux. This observed correlation deviates by about 2-3 standard deviations from the expected correlation of 4.3$\%$ as obtained from theoretical predictions under the assumption of various hadronic interaction models

The T2K experiment presents new measurements of neutrino oscillation parameters using $19.7(16.3)\times10^{20}$ protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional $4.7\times10^{20}$ POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on $\sin^2θ_{13}$ and the impact of priors on the $δ_\mathrm{CP}$ measurement. Both analyses prefer the normal mass ordering and upper octant of $\sin^2θ_{23}$ with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on $\sin^2θ_{13}$ from reactors, $\sin^2θ_{23}=0.561^{+0.021}_{-0.032}$ using Feldman--Cousins corrected intervals, and $Δm^2_{32}=2.494_{-0.058}^{+0.041}\times10^{-3}~\mathrm{eV^2}$ using constant $Δχ^{2}$ intervals. The CP-violating phase is constrained to $δ_\mathrm{CP}=-1.97_{-0.70}^{+0.97}$ using Feldman--Cousins corrected intervals, and $δ_\mathrm{CP}=0,π$ is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than $2σ$ credible level using a flat prior in $δ_\mathrm{CP}$, and just below $2σ$ using a flat prior in $\sinδ_\mathrm{CP}$. When the external constraint on $\sin^2θ_{13}$ is removed, $\sin^2θ_{13}=28.0^{+2.8}_{-6.5}\times10^{-3}$, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

The sensitivity of cosmology to the total neutrino mass scale $\Sigma m_\nu$ is approaching the minimal values required by oscillation data. We study quantitatively possible tensions between current and forecasted cosmological and terrestrial neutrino mass limits by applying suitable statistical tests such as Bayesian suspiciousness, parameter goodness-of-fit tests, or a parameter difference test. In particular, the tension will depend on whether the normal or the inverted neutrino mass ordering is assumed. We argue, that it makes sense to reject inverted ordering from the cosmology/oscillation comparison only if data are consistent with normal ordering. Our results indicate that, in order to reject inverted ordering with this argument, an accuracy on the sum of neutrino masses $\sigma ({m_\nu})$ of better than 0.02~eV would be required from future cosmological observations.

In this article, we study the potential of direct detection experiments to explore the parameter space of general non-standard neutrino interactions (NSI) via solar neutrino scattering. Due to their sensitivity to neutrino-electron and neutrino-nucleus scattering, direct detection provides a complementary view of the NSI landscape to that of spallation sources and neutrino oscillation experiments. In particular, the large admixture of tau neutrinos in the solar flux makes direct detection experiments well-suited to probe the full flavour space of NSI. To study this, we develop a re-parametrisation of the NSI framework that explicitly includes a variable electron contribution and allows for a clear visualisation of the complementarity of the different experimental sources. Using this new parametrisation, we explore how previous bounds from spallation source and neutrino oscillation experiments are impacted. For the first time, we compute limits on NSI from the first results of the XENONnT and LUX-ZEPLIN experiments, and we obtain projections for future xenon-based experiments. These computations have been performed with our newly developed software package, SNuDD. Our results demonstrate the importance of using a more general NSI parametrisation and indicate that next generation direct detection experiments will become powerful probes of neutrino NSI.

There is growing interest in viable quantum theories with PT-symmetric non-Hermitian Hamiltonians, but a formulation of transition matrix elements consistent with positivity and perturbative unitarity has so far proved elusive. This Letter provides such a formulation, which relies crucially on the ability to span the state space in such a way that the interaction and energy eigenstates are orthonormal with respect to the same positive-definite inner product. We mention possible applications to the oscillations of mesons and neutrinos.

We scrutinize the hypothesis that gauge singlet fermions -- sterile neutrinos -- interact with Standard Model particles through the transition magnetic moment portal. These interactions lead to the production of sterile neutrinos in supernovae followed by their decay into photons and active neutrinos which can be detected at $\gamma$-ray telescopes and neutrino detectors, respectively. We find that the non-observation of active neutrinos and photons from sterile-neutrino decay associated to SN1987A yields the strongest constraints to date on magnetic-moment-coupled sterile neutrinos if their masses are inside a $0.1-100$ MeV window. Assuming a near-future galactic supernova explosion, we estimate the sensitivity of several present and near-future experiments, including Fermi-LAT, e-ASTROGAM, DUNE, and Hyper-Kamiokande, to magnetic-moment-coupled sterile neutrinos. We also study the diffuse photon and neutrino fluxes produced in the decay of magnetic-moment coupled sterile neutrinos produced in all past supernova explosions and find that the absence of these decay daughters yields the strongest constraints to date for sterile neutrino masses inside a $1-100$ keV window.

Most antineutrinos produced in a nuclear reactor have energies below the inverse beta decay threshold, and have not yet been detected. We show that a coherent elastic neutrino-nucleus scattering experiment with an ultra-low energy threshold like NUCLEUS can measure the flux of reactor neutrinos below 1.8 MeV. Using a regularized unfolding procedure, we find that a meaningful upper bound can be placed on the low energy flux, but the existence of the neutron capture component cannot be established.

The neutrino oscillations offer great potential for probing new physics effects beyond the Standard Model. Any additional effect on neutrino oscillations can help understand the nature of these non-standard effects. The violation of fundamental symmetries may appear as new physics effects in various neutrino experiments. Lorentz symmetry is one such fundamental symmetry in nature, the violation of which implies a breakdown of space-time symmetry. The Lorentz Invariance Violation (LIV) is intrinsic in nature and its effects exist even in a vacuum. Neutrinos can be an intriguing probe for exploring such violations of Lorentz symmetry. The effect of violation of Lorentz Invariance can be explored through the impact on the neutrino oscillation probabilities. The effect of LIV is treated as a perturbation to the standard neutrino Hamiltonian considering the Standard Model Extension (SME) framework. In this work, we have probed the effect of LIV on the neutrino oscillation measurements considering the Deep Underground Neutrino Experiment (DUNE) as a case study. The inclusion of LIV affects various neutrino oscillation parameters as it modifies the standard neutrino oscillation probabilities. We looked into the capability of DUNE in constraining the LIV parameters and then explored the impact of CPT-violating LIV terms on the mass-induced neutrino oscillation probabilities. We have also probed the influence of LIV parameters on the CP-measurement sensitivity at DUNE.

General classical arguments on the time evolution of the phase-space density can be used to derive constraints on the mass of particle candidates for the cosmological dark matter (DM). The resulting Tremaine-Gunn limit is extremely useful in constraining particle DM models. In certain models, however, the DM particle mass varies appreciably over time. In this work, we generalize the phase-space limits on possible DM particle masses to these scenarios. We then examine the ensuing cosmological implications on the effective DM equation of state and indirect DM detection.

Neutrino oscillation in the matter could get affected by the sub-dominant, yet unknown, non-standard interactions. The upcoming long-baseline (LBL) neutrino experiments will be sensitive to these effects and can provide information on the unknown oscillation parameter values. In this article, we study the parameter degeneracies that can occur in DUNE, T2HK experiments, and a combination of both due to nonstandard interactions (NSI), arising simultaneously, from two different off-diagonal sectors, i.e., $e-\mu$ and $e-\tau$. We derive constraints on both the NSI sectors using the combined datasets of NO$\nu$A and T2K. Our analysis reveals a significant impact that dual NSIs may have on the sensitivity of atmospheric mixing angle $\theta_{23}$ in the normal ordering (NO) case. Furthermore, when non-standard interaction from the $e-\mu$ and $e-\tau$ sectors are included, we see significant changes in the probabilities for DUNE, T2HK, and as well as a combined analysis involving both. Moreover, the CP sensitivity gets affected significantly due to the presence of dual NSIs, and, in addition, the CP asymmetry also exhibits an appreciable difference.

Long-baseline (LBL) accelerator neutrino oscillation experiments, such as NOvA and T2K in the current generation, and DUNE-LBL and HK-LBL in the coming years, will measure the remaining unknown oscillation parameters with excellent precision. These analyses assume external input on the so-called ``solar parameters,'' $\theta_{12}$ and $\Delta m^2_{21}$, from solar experiments such as SNO, SK, and Borexino, as well as reactor experiments like KamLAND. Here we investigate their role in long-baseline experiments. We show that, without external input on $\Delta m^2_{21}$ and $\theta_{12}$, the sensitivity to detecting and quantifying CP violation is significantly, but not entirely, reduced. Thus long-baseline accelerator experiments can actually determine $\Delta m^2_{21}$ and $\theta_{12}$, and thus all six oscillation parameters, without input from \emph{any} other oscillation experiment. In particular, $\Delta m^2_{21}$ can be determined; thus DUNE-LBL and HK-LBL can measure both the solar and atmospheric mass splittings in their long-baseline analyses alone. While their sensitivities are not competitive with existing constraints, they are very orthogonal probes of solar parameters and provide a key consistency check of a less probed sector of the three-flavor oscillation picture. Furthermore, we also show that the true values of $\Delta m^2_{21}$ and $\theta_{12}$ play an important role in the sensitivity of other oscillation parameters such as the CP violating phase $\delta$.

If neutrinos carry non-zero electric charge, they would interact directly with photons. This would induce a phase shift along the photon path in the optical experiment. We propose a novel idea to detect this phase shift induced by cosmic neutrino background (CNB) and the photon interaction using laser interferometry experiment. We show that our setup can probe the CNB neutrino charge in the order of $10^{-18} \,e- 10^{-17}\, e$. This is quite competitive with the existing upper bound on neutrino charge from both laboratory experiments and astrophysical observations.

We discuss the improvement of the sensitivity of ESS$\nu$SB to the discovery of CP violation and to new neutrino physics which can be obtained with a two-detector fit of the data of the near and far detectors. In particular, we consider neutrino non-standard interactions generated by very heavy vector mediators, nonunitary neutrino mixing, and neutrino oscillations due to the mixing of the ordinary active neutrinos with a light sterile neutrino.

A $Z'$ boson associated with a broken $U(1)_{L_{\mu} - L_{\tau}}$ gauge symmetry offers an economical solution to the long-standing $g_\mu-2$ anomaly, confirmed and strengthened by recent measurements at Fermilab. Here, we revisit the impact of such a $Z'$ on the spectrum of high-energy astrophysical neutrinos, as measured by the IceCube experiment. This spectrum has been observed to exhibit a dip-like feature at $E_{\nu} \sim 0.2-1 \, {\rm PeV}$, which could plausibly arise from the physics of the sources themselves, but could also be the consequence of high-energy neutrinos resonantly scattering with the cosmic neutrino background, mediated by a $Z'$ with a mass on the order of $m_{Z'} \sim 10 \, {\rm MeV}$. In this study, we calculate the impact of such a $Z'$ on the high-energy neutrino spectrum for a variety of model parameters and source distributions. For couplings that can resolve the $g_{\mu}-2$ anomaly, we find that this model could self-consistently produce a spectral feature that is consistent with IceCube's measurement, in particular if the neutrinos observed by IceCube predominantly originate from high-redshift sources.

In the era of precision measurements of the neutrino oscillation parameters, upcoming neutrino experiments will also be sensitive to physics beyond the Standard Model. KM3NeT/ORCA is a neutrino detector optimised for measuring atmospheric neutrinos from a few GeV to around 100 GeV. In this paper, the sensitivity of the KM3NeT/ORCA detector to neutrino decay has been explored. A three-flavour neutrino oscillation scenario, where the third neutrino mass state $\nu_3$ decays into an invisible state, e.g. a sterile neutrino, is considered. We find that KM3NeT/ORCA would be sensitive to invisible neutrino decays with $1/\alpha_3=\tau_3/m_3 < 180$~$\mathrm{ps/eV}$ at $90\%$ confidence level, assuming true normal ordering. Finally, the impact of neutrino decay on the precision of KM3NeT/ORCA measurements for $\theta_{23}$, $\Delta m^2_{31}$ and mass ordering have been studied. No significant effect of neutrino decay on the sensitivity to these measurements has been found.

In-ice radio detectors are a promising tool for the discovery of EeV neutrinos. For astrophysics, the implications of such a discovery will rely on the reconstruction of the neutrino arrival direction. This paper describes a first complete neutrino arrival direction reconstruction for detectors employing deep antennas such as RNO-G or planning to employ them like IceCube-Gen2. We will didactically introduce the challenges of neutrino direction reconstruction using radio emission in ice, elaborate on the detail of the algorithm used, and describe the obtainable performance based on a simulation study and discuss its implication for astrophysics.

Scalar ultra-light dark matter (ULDM) interacting with neutrinos can induce, under certain conditions, time-dependent modifications to neutrino oscillation probabilities. The limit in which the ULDM perturbation can be treated as constant throughout the neutrino propagation time has been addressed by several previous works. We complement these by systematically analyzing the opposite limit -- accounting for the temporal-variations of the ULDM potential by solving time-dependent Schr\"odinger equations. In particular, we study a novel two-generations-like CP violating (CPV) signature unique to rapidly oscillating ULDM. We derive the leading order, time-dependent, corrections to the oscillation probabilities, both for CP conserving (CPC) and CPV couplings, and explain how they can be measured in current and future experiments.

Forthcoming fixed-target coherent elastic neutrino-nucleus scattering experiments aim at measurements with $\cal{O}(\text{tonne})$-scale detectors and substantially reduced systematic and statistical uncertainties. With such high quality data, the extraction of point-neutron distributions mean-square radii requires a better understanding of possible theoretical uncertainties. We quantify the impact of single-nucleon electromagnetic mean-square radii on the weak-charge form factor and compare results from weak-charge form factor parametrizations and weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors, including nucleon form factors $Q$-dependent terms up to order $Q^2$. We assess as well the differences arising from results derived using weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors and a model-independent approach based solely on the assumption of spherically symmetric nuclear ground state. We demonstrate the impact of the main effects by assuming pseudo-data from a one-tonne LAr detector and find that, among the effects and under the assumptions considered in this paper, weak-charge form factor parametrizations and weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors enable the extraction of the $^{40}\text{Ar}$ point-neutron distribution mean-square radius with a $\sim 15\%$ accuracy. With a substantial reduction of the beam-related neutron and steady-state backgrounds a $\sim 1\%$ precision extraction seems feasible, using either of the two approaches.

Nonunitarity can arise in neutrino oscillation when the matrix with elements $\mathbf{U}_{\alpha i}$ which relate the neutrino flavor $\alpha$ and mass $i$ eigenstates is not unitary when sum over the kinematically accessible mass eigenstates or over the three Standard Model flavors. We review how high scale nonunitarity arises after integrating out new physics which is not accessible in neutrino oscillation experiments. In particular, we stress that high scale unitarity violation is only apparent and what happens is that the neutrino flavor states become nonorthogonal due to new physics. Since the flavor space is complete, unitarity has to be preserved in time evolution and that the probabilities of a flavor state oscillates to all possible flavor states always sum up to unity. We highlight the need to modify the expression of probability to preserve unitarity when the flavor states are nonorthogonal. We will continue to call this high scale unitarity violation in reference to a nonunitary $\mathbf{U}$. We contrast this to the low scale nonunitarity scenario in which there are new states accessible in neutrino oscillation experiments but the oscillations involving these states are fast enough such that they are averaged out. We further derive analytical formula for the neutrino oscillation amplitude involving $N$ neutrino flavors without assuming a unitarity $\mathbf{U}$ which allows us to prove a theorem that if $\left(\mathbf{U}\mathbf{U}^{\dagger}\right)_{\alpha\beta}=0$ for all $\alpha\neq\beta$, then the neutrino oscillation probability in an arbitrary matter potential is indistinguishable from the unitarity scenario. Independently of matter potential, while nonunitarity effects for high scale nonunitarity scenario disappear as $\left(\mathbf{U}\mathbf{U}^{\dagger}\right)_{\alpha\beta}\to 0$ for all $\alpha\neq\beta$, low scale nonunitarity effects can remain.

The Klein-Gordon equation for a scalar field sourced by a spherically symmetric background is an interesting second-order differential equation with applications in particle physics, astrophysics, and elsewhere. Here we present solutions for generic source density profiles in the case where the scalar field has no interactions or a mass term. For a $\lambda\phi^4$ self-interaction term, we provide the necessary expressions for a numerical computation, an algorithm to numerically match the initial conditions from infinity to the origin, and an accurate guess of that initial condition. We also provide code to perform the numerical calculations that can be adapted for arbitrary density profiles.

The LHC produces an intense beam of highly energetic neutrinos of all three flavors in the forward direction, and the Forward Physics Facility (FPF) has been proposed to house a suite of experiments taking advantage of this opportunity. In this study, we investigate the FPF's potential to probe the neutrino electromagnetic properties, including neutrino millicharge, magnetic moment, and charge radius. We find that, due to the large flux of tau neutrinos at the LHC, the FPF detectors will be able to provide the strongest laboratory-based sensitivity to the tau neutrino magnetic moment and millicharge by searching for excess in low recoil energy electron scattering events. We also find that, by precisely measuring the rate of neutral current deep inelastic scattering events, the FPF detectors have the potential to obtain the strongest experimental bounds on the neutrino charge radius for the electron neutrino, and one of the leading bounds for the muon neutrino flavor. The same signature could also be used to measure the weak mixing angle, and we estimate that $\sin^2 \theta_W$ could be measured to about $3\%$ precision at a scale $Q \sim 10$ GeV, shedding new light on the long-standing NuTeV anomaly.

Light sterile neutrinos with a mass of $\sim 1$ eV continue to be interesting due to multiple hints from terrestrial experiments. This simple hypothesis suffers from strong astrophysical constraints, in particular from the early universe as well as solar neutrinos. We develop a cosmologically viable proposal consistent with the terrestrial hints, as well as solar constraints, by sourcing the sterile neutrino's mass from ordinary matter via an ultralight scalar $φ$ which can also be the dark matter. In this scenario, the experimentally implied $\sim 1$ eV sterile neutrino mass is a local value and changes throughout spacetime.

The discrepancy between the value of Hubble constant measured by CMB observations and local low-redshift based observations has proposed many solutions which require the existence of Physics beyond Standard Model (SM). One of the interesting solutions is based on considering the strong self-interaction between Standard Model (SM) neutrinos through an additional scalar/vector mediator. Interestingly, the strong self-interaction between SM neutrinos also play an important role in obtaining KeV-sterile neutrino as a viable Dark Matter (DM) candidate through the famous Dodelson-Widrow mechanism. In this work, we have tried to find the synergy between the parameter space of active-sterile neutrino mixing vs mass of sterile neutrino allowed by Hubble tension solution and the requirement of getting KeV-sterile neutrino as DM candidate. Interestingly, we get a large amount of parameter space that is consistent with both the requirements and also free from X-Ray constraints. Finally, we have embedded this scenario in a consistent supersymmetric model of particle physics. In this framework, we have shown that the value of sterile neutrino mass, SM neutrino mass and the required mixing angle can be naturally obtained by considering the supersymmetry breaking scale to be around O(10) TeV. Thus, it would give an interesting testing ground for supersymmetry as well as signatures of Warm Dark Matter (WDM).

The IceCube collaboration has observed the first steady-state point source of high-energy neutrinos, coming from the active galaxy NGC 1068. If neutrinos interacted strongly enough with dark matter, the emitted neutrinos would have been impeded by the dense spike of dark matter surrounding the supermassive black hole at the galactic center, which powers the emission. We derive a stringent upper limit on the scattering cross section between neutrinos and dark matter based on the observed events and theoretical models of the dark matter spike. The bound can be stronger than that obtained by the single IceCube neutrino event from the blazar TXS 0506+056 for some spike models.

Sterile neutrinos only interact with the Standard Model through the neutrino sector, and thus represent a simple dark matter (DM) candidate with many potential astrophysical and cosmological signatures. Recently, sterile neutrinos produced through self-interactions of active neutrinos have received attention as a particle candidate that can yield the entire observed DM relic abundance without violating the most stringent constraints from X-ray observations. We examine consistency of this production mechanism with the abundance of small-scale structure in the universe, as captured by the population of ultra-faint dwarf galaxies orbiting the Milky Way, and derive a lower bound on the sterile-neutrino particle mass of $37.2$ keV. Combining these results with previous limits from particle physics and astrophysics excludes $100\%$ sterile neutrino DM produced by strong neutrino self-coupling, mediated by a heavy ($\gtrsim 1~\mathrm{GeV}$) scalar particle; however, data permits sterile-neutrino DM production via a light mediator.

Minerals are solid state nuclear track detectors - nuclear recoils in a mineral leave latent damage to the crystal structure. Depending on the mineral and its temperature, the damage features are retained in the material from minutes (in low-melting point materials such as salts at a few hundred degrees C) to timescales much larger than the 4.5 Gyr-age of the Solar System (in refractory materials at room temperature). The damage features from the $O(50)$ MeV fission fragments left by spontaneous fission of $^{238}$U and other heavy unstable isotopes have long been used for fission track dating of geological samples. Laboratory studies have demonstrated the readout of defects caused by nuclear recoils with energies as small as $O(1)$ keV. This whitepaper discusses a wide range of possible applications of minerals as detectors for $E_R \gtrsim O(1)$ keV nuclear recoils: Using natural minerals, one could use the damage features accumulated over $O(10)$ Myr$-O(1)$ Gyr to measure astrophysical neutrino fluxes (from the Sun, supernovae, or cosmic rays interacting with the atmosphere) as well as search for Dark Matter. Using signals accumulated over months to few-years timescales in laboratory-manufactured minerals, one could measure reactor neutrinos or use them as Dark Matter detectors, potentially with directional sensitivity. Research groups in Europe, Asia, and America have started developing microscopy techniques to read out the $O(1) - O(100)$ nm damage features in crystals left by $O(0.1) - O(100)$ keV nuclear recoils. We report on the status and plans of these programs. The research program towards the realization of such detectors is highly interdisciplinary, combining geoscience, material science, applied and fundamental physics with techniques from quantum information and Artificial Intelligence.

Ultralight dark matter (ULDM) is usually taken to be a single scalar field. Here we explore the possibility that ULDM consists of $N$ light scalar fields with only gravitational interactions. This configuration is more consistent with the underlying particle physics motivations for these scenarios than a single ultralight field. ULDM halos have a characteristic granular structure that increases stellar velocity dispersion and can be used as observational constraints on ULDM models. In multifield simulations, we find that inside a halo the amplitude of the total density fluctuations decreases as $1/\sqrt{N}$ and that the fields do not become significantly correlated over cosmological timescales. Smoother halos heat stellar orbits less efficiently, reducing the velocity dispersion relative to the single field case and thus weakening the observational constraints on the field mass. Analytically, we show that for $N$ equal-mass fields with mass $m$ the ULDM contribution to the stellar velocity dispersion scales as $1/(N m^3)$. Lighter fields heat the most efficiently and if the smallest mass $m_L$ is significantly below the other field masses the dispersion scales as $1/(N^2 m_L^3)$.

Using an effective field theory approach, we study coherent neutrino scattering on nuclei, in the setup pertinent to the COHERENT experiment. We include non-standard effects both in neutrino production and detection, with an arbitrary flavor structure, with all leading Wilson coefficients simultaneously present, and without assuming factorization in flux times cross section. A concise description of the COHERENT event rate is obtained by introducing three generalized weak charges, which can be associated (in a certain sense) to the production and scattering of $\nu_e$, $\nu_\mu$ and $\bar{\nu}_\mu$ on the nuclear target. Our results are presented in a convenient form that can be trivially applied to specific New Physics scenarios. In particular, we find that existing COHERENT measurements provide percent level constraints on two combinations of Wilson coefficients. These constraints have a visible impact on the global SMEFT fit, even in the constrained flavor-blind setup. The improvement, which affects certain 4-fermion LLQQ operators, is significantly more important in a flavor-general SMEFT. Our work shows that COHERENT data should be included in electroweak precision studies from now on.

The 2021-22 High-Energy Physics Community Planning Exercise (a.k.a. ``Snowmass 2021'') was organized by the Division of Particles and Fields of the American Physical Society. Snowmass 2021 was a scientific study that provided an opportunity for the entire U.S. particle physics community, along with its international partners, to identify the most important scientific questions in High Energy Physics for the following decade, with an eye to the decade after that, and the experiments, facilities, infrastructure, and R&D needed to pursue them. This Snowmass summary report synthesizes the lessons learned and the main conclusions of the Community Planning Exercise as a whole and presents a community-informed synopsis of U.S. particle physics at the beginning of 2023. This document, along with the Snowmass reports from the various subfields, will provide input to the 2023 Particle Physics Project Prioritization Panel (P5) subpanel of the U.S. High-Energy Physics Advisory Panel (HEPAP), and will help to guide and inform the activity of the U.S. particle physics community during the next decade and beyond.

A weakly coupled and light dark photon coupling to lepton charges $L_\mu-L_\tau$ is an intriguing dark matter candidate whose coherent oscillations alter the dispersion relations of leptons. We study how this effect modifies the dynamics of neutrino flavor conversions, focusing on long baseline and solar oscillations. We analyze data from the T2K, SNO, and Super-Kamiokande experiments in order to obtain world-leading limits on the dark photon gauge coupling for masses below $\sim 10^{-11}\,\mathrm{eV}$. Degeneracies between shifts in the neutrino mass-squared differences and mixing angles and the new physics effect significantly relax the current constrains on the neutrino vacuum oscillation parameters.

This book chapter presents an overview of the historical experimental and theoretical developments in neutrino physics and astrophysics and also the physical properties of neutrinos, as well as the physical processes involving neutrinos. It also discusses the role of neutrinos in astrophysics and cosmology. Correction to tex file made.

In this article, we study the on-shell production of low-mass vector mediators from neutrino-antineutrino coalescence in the core of proto-neutron stars. Taking into account the radial dependence of the density, energy, and temperature inside the proto-neutron star, we compute the neutrino-antineutrino interaction rate in the star interior in the well-motivated $U(1)_{L_{\mu}-L_{\tau}}$ model. First, we determine the values of the coupling above which neutrino-antineutrino interactions dominate over the Standard Model neutrino-nucleon scattering. We argue that, although in this regime a redistribution of the neutrino energies might take place, making low-energy neutrinos more trapped, this only affects a small part of the neutrino population and it cannot be constrained with the SN 1987A data. Thus, contrary to previous claims, the region of the parameter space where the $U(1)_{L_{\mu}-L_{\tau}}$ model explains the discrepancy in the muon anomalous magnetic moment is not ruled out. We then focus on small gauge couplings, where the decay length of the new gauge boson is larger than the neutrino-nucleon mean free path, but still smaller than the size of proto-neutron star. We show that in this regime, the on-shell production of a long-lived $Z'$ and its subsequent decay into neutrinos can significantly reduce the duration of the neutrino burst, probing values of the coupling below ${\cal O}(10^{-7})$ for mediator masses between 10 and 100 MeV. This disfavours new areas of the parameter space of the $U(1)_{L_{\mu}-L_{\tau}}$ model.

We examine the scope of the MOMENT experiment in the context of CP violation searches with the presence of extra eV scale sterile neutrino. MOMENT is a proposed short baseline neutrino oscillation experiment using muon beams for neutrinos production, making it advantageous over $\pi_0$ background and other technical difficulties. We work over the first oscillation maxima which matches the peak value of flux with a run time of 5 years for both neutrino and anti-neutrino modes. We perform the bi-probability studies for both 3 and 3+1 flavor mixing schemes. The CP violation sensitivities arising from the fundamental CP phase $\delta_{13}$ and unknown CP phase $\delta_{14}$ are explored at the firm footing. The slight deteriorates are observed in CP violations induced by $\delta_{13}$ as the presence of sterile neutrino is considered. We also look at the reconstruction of CP violations phases $\delta_{13}$ and $\delta_{14}$ and the MOMENT experiment shows significant capabilities in the precise measurement of $\delta_{13}$ phase.

The origin of the bulk of the high-energy astrophysical neutrinos seen by IceCube, with TeV--PeV energies, is unknown. If they are made in photohadronic, i.e., proton-photon, interactions in astrophysical sources, this may manifest as a bump-like feature in their diffuse flux, centered around a characteristic energy. We search for evidence of this feature, allowing for variety in its shape and size, in 7.5 years of High-Energy Starting Events (HESE) collected by the IceCube neutrino telescope, and make forecasts using larger data samples from upcoming neutrino telescopes. Present-day data reveals no evidence of bump-like features, which allows us to constrain candidate populations of photohadronic neutrino sources. Near-future forecasts show promising potential for stringent constraints or decisive discovery of bump-like features. Our results provide new insight into the origins of high-energy astrophysical neutrinos, complementing those from point-source searches.

Nuclear reactors represent a promising neutrino source for CE$\nu$NS (coherent-elastic neutrino-nucleus scattering) searches. However, reactor sites also come with high ambient neutron flux. Neutron capture-induced nuclear recoils can create a spectrum that strongly overlaps the CE$\nu$NS signal for recoils $\lesssim$\,100\,eV for nuclear reactor measurements in silicon or germanium detectors. This background can be particularly critical for low-power research reactors providing a moderate neutrino flux. In this work we quantify the impact of this background and show that, for a measurement 10\,m from a 1\,MW reactor, the effective thermal neutron flux should be kept below $\sim$~7$\times$~10$^{-4}$\,n/cm$^2$s so that the CE$\nu$NS events can be measured at least at a 5$\sigma$ level with germanium detectors in 100~kg\,yr exposure time. This flux corresponds to 60\% of the sea-level flux but needs to be achieved in a nominally high-flux (reactor) environment. Improved detector resolution can help the measurements, but the thermal flux is the key parameter for the sensitivity of the experiment. For silicon detectors, the constraint is even stronger and thermal neutron fluxes must be near an order of magnitude lower. This constraint highlights the need of an effective thermal neutron mitigation strategy for future low threshold CE$\nu$NS searches. In particular, the neutron capture-induced background can be efficiently reduced by active veto systems tagging the deexcitation gamma following the capture.

We revisit neutrino oscillations in constant matter density for a number of different scenarios: three flavors with the standard Wolfenstein matter potential, four flavors with standard matter potential and three flavors with non-standard matter potentials. To calculate the oscillation probabilities for these scenarios one must determine the eigenvalues and eigenvectors of the Hamiltonians. We use a method for calculating the eigenvalues that is well known, determination of the zeros of determinant of matrix $(\lambda I -H)$, where H is the Hamiltonian, I the identity matrix and $\lambda$ is a scalar. To calculate the associated eigenvectors we use a method that is little known in the particle physics community, the calculation of the adjugate (transpose of the cofactor matrix) of the same matrix, $(\lambda I -H)$. This method can be applied to any Hamiltonian, but provides a very simple way to determine the eigenvectors for neutrino oscillation in matter, independent of the complexity of the matter potential. This method can be trivially automated using the Faddeev-LeVerrier algorithm for numerical calculations. For the above scenarios we derive a number of quantities that are invariant of the matter potential, many are new such as the generalization of the Naumov-Harrison-Scott identity for four or more flavors of neutrinos. We also show how these matter potential independent quantities become matter potential dependent when off-diagonal non-standard matter effects are included.

Motivated by flavour symmetry models, we construct theories based on a low-energy limit featuring lepton flavour triality that have the flavour-violating decays $\tau^\pm \to \mu^\pm \mu^\pm e^\mp$ and $\tau^\pm \to e^\pm e^\pm \mu^\mp$ as the main phenomenological signatures of physics beyond the standard model. These decay modes are expected to be probed in the near future with increased sensitivity by the Belle II experiment at the SuperKEKB collider. The simple standard model extensions featured have doubly-charged scalars as the mediators of the above decay processes. The phenomenology of these extensions is studied here in detail.

We discuss in detail the dependence of the Gallium Anomaly on the detection cross section. We provide updated values of the size of the Gallium Anomaly and find that its significance is larger than about $5\sigma$ for all the detection cross section models. We discuss the dependence of the Gallium Anomaly on the assumed value of the half life of ${}^{71}\text{Ge}$, which determines the cross sections of the transitions from the ground state of ${}^{71}\text{Ga}$ to the ground state of ${}^{71}\text{Ge}$. We show that a value of the ${}^{71}\text{Ge}$ half life which is larger than the standard one can reduce or even solve the Gallium Anomaly. Considering the short-baseline neutrino oscillation interpretation of the Gallium Anomaly, we show that a value of the ${}^{71}\text{Ge}$ half life which is larger than the standard one can reduce the tension with the results of other experiments. Since the standard value of the ${}^{71}\text{Ge}$ half life was measured in 1985, we advocate the importance of new measurements with modern technique and apparatus for a better assessment of the Gallium Anomaly.

Muons have a similar latency/energy correlation from pion decay as do the neutrinos, and hence in each time-slice in a stroboscopic analysis measurements of their momentum spectra can reduce systematic uncertainties due to flux. There are, however, unique issues for muons: 1) during standard neutrino data-taking muon measurements in the forward direction must be in formidable high-flux high-radiation environments; 2) because of the very high incident hadron flux in the Absorber Hall, muons must be detected after a thick absorber, imposing a range cutoff at a momentum much above the minimum neutrino momentum of interest; 3) the muon velocity, unlike that of neutrinos, differs from $c$, and so the muon detected time will require correction for the muon flight path, requiring measurement of the muon momentum; 4) multiple scattering is significant for low-momentum muons, and so a `good geometry' is essential for precision muon flux measurements; and 5) developments in psec timing allow muon momenta in the momentum region of interest to be measured precisely by time-of-flight over short distances with photodetectors of a few-psec resolution. Here we advocate that a program of extensive precise low-intensity muon momentum spectrum measurements be carried out early in the LBNF program before the Absorber Hall becomes too hot. The low-momentum muon spectra taken in this experiment would be cross-normalized to the high-intensity neutrino data through the currently planned muon monitors which can operate in both the low and high intensity geometries. While beyond the scope of uniquely muon-related issues, the note includes a proposal for an long-base-line oscillation analysis strategy that exploits stroboscopic information for both neutrinos and muons to reduce systematic uncertainties on the neutrino fluxes and event selection in Far and Near detectors.

We consider the effects of strong gravitational lensing by galaxy-scale deflectors on the observations of high-energy (E$\gg$GeV) neutrinos (HEN). For HEN at cosmological distances, the optical depth for multiple imaging is $\sim 10^{-3}$, implying that while we do not expect any multiply imaged HEN with present samples, next-generation experiments should be able to detect the first such event. We then present the distribution of expected time delays to aid in the identification of such events, in combination with directional and energy information. In order to assist in the evaluation of HEN production mechanisms, we illustrate how lensing affects the observed number counts for a variety of intrinsic luminosity functions of the source population. Finally, we see that the lensing effects on the cosmic neutrino background flux calculation would be negligible by taking kpc-scale jets as an example.

Analytic results are presented for the probability of detecting an electron neutrino after passage through a resonant oscillation region. If the electron neutrino is produced far above the resonance density, this probability is simply given by $\langle \,P_{\nu_e} \, \rangle \approx \sin^2 \theta_0+ P_\text{x} \cos 2 \theta_0$, where $\theta_0$ is the vacuum mixing angle. The probability is averaged over the production as well as the detection positions of the neutrino and $P_\text{x} $ is the Landau-Zener transition probability between adiabatic states. Finally, this result is applied to resonance oscillations within the solar interior.

Recently, the LHAASO collaboration has observed the gamma rays of energies up to ten TeV from the gamma-ray burst GRB221009A, which has stimulated the community of astronomy, particle physics and astrophysics to propose various possible interpretations. In this paper, we put forward a viable scenario that neutrinos are produced together with TeV photons in the gamma-ray burst and gradually decay into the axion-like particles, which are then converted into gamma rays in the galactic magnetic fields. In such a scenario, the tension between previous axion-like particle interpretations and the existing observational constraints on the relevant coupling constant and mass can be relaxed.

Results from the experiments like LSND, and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations; in particular, it can give rise to additional degeneracies due to new sterile parameters. In our work, we investigate how the sensitivity to determine the octant of the neutrino mixing angle $\theta_{23}$ is affected by introducing a sterile neutrino to the standard neutrino oscillation framework. We compute the oscillation probabilities in presence of a sterile neutrino, analytically, using the approximation that $\Delta_{21}$, the smallest mass squared difference, is zero. We use these probabilities to understand the degeneracies analytically at different baselines. We present our results of the sensitivity to octant of $\theta_{23}$ for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector without any charge identification capability. In addition, we include the charge tagging capability of muon capture in argon which allows one to differentiate between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in a similar experimental setup is also delineated. We observe that by combining simulated data from the beam and atmospheric neutrinos (including charge-id for muons), the sensitivity to the octant of $\theta_{23}$ for true values of $\theta_{23}=41^\circ(49^\circ)$ exceeds $4\sigma(3\sigma)$ for more than $50\%$ values of true $\delta_{13}$.

This is the report from the Snowmass NF01 topical group and colleagues on the current status and expected future progress to understand the three-flavor neutrino oscillation picture.

The recent observation of NGC 1068 by the IceCube Neutrino Observatory has opened a new window to neutrino physics with astrophysical baselines. In this Letter, we propose a new method to probe the nature of neutrino masses using these observations. In particular, our method enables searching for signatures of pseudo-Dirac neutrinos with mass-squared differences that reach down to $\delta m^2 \gtrsim 10^{-21}~\text{eV}^2$, improving the reach of terrestrial experiments by more than a billion. Finally, we discuss how the discovery of a constellation of neutrino sources can further increase the sensitivity and cover a wider range of $\delta m^2$ values.

We argue that the reflection of relic neutrinos from the surface of the Earth results in a significant local $\nu-\bar{\nu}$ asymmetry, far exceeding the expected primordial lepton asymmetry. The net fractional electron neutrino number $\frac{n_{\nu_e}-n_{\bar{\nu}_e}}{n_{\nu_e}}$ is up to $\mathcal{O}(10^5) \sqrt{\frac{m_\nu}{0.1~\text{eV}}}$ larger than that implied by the baryon asymmetry. This enhancement is due to the weak 4-Fermi repulsion of the $\nu_e$ from ordinary matter which slows down the $\nu_e$ near the Earth's surface, and to the resulting evanescent neutrino wave that penetrates below the surface. This repulsion thus creates a net $\nu_e$ overdensity in a shell $\sim 7~\text{meters} \sqrt{\frac{0.1~\text{eV}}{m_\nu}}$ thick around the Earth's surface. Similarly the repulsion between $\bar{\nu}_\mu$ or $\bar{\nu}_\tau$ and ordinary matter creates an overdensity of $\bar{\nu}_{\mu, \tau}$ of similar size. These local enhancements increase the size of $\mathcal{O}(G_F)$ torques of the $C\nu B$ on spin-polarized matter by a factor of order $10^5$. In addition, they create a gradient of the net neutrino density which naturally provides a way out of the forty-year-old ``no-go'' theorems on the vanishing of $\mathcal{O}(G_F)$ forces. The torque resulting from such a gradient force can be $10^8$ times larger than that of earlier proposals. Although the size of these effects is still far from current reach, they may point to new directions for $C\nu B$ detection.

The IceCube Neutrino Observatory at the South Pole can provide unique tests of muon production models in extensive air showers by measuring both the low-energy (GeV) and high-energy (TeV) muon components. We present here a measurement of the TeV muon content in near-vertical air showers detected with IceTop in coincidence with IceCube. The primary cosmic-ray energy is estimated from the dominant electromagnetic component of the air shower observed at the surface. The high-energy muon content of the shower is studied based on the energy losses measured in the deep detector. Using a neural network, the primary energy and the multiplicity of TeV muons are estimated on an event-by-event basis. The baseline analysis determines the average multiplicity as a function of the primary energy between 2.5 PeV and 250 PeV using the hadronic interaction model Sibyll 2.1. Results obtained using simulations based on the post-LHC models QGSJet-II.04 and EPOS-LHC are presented for primary energies up to 100 PeV. For all three hadronic interaction models, the measurements of the TeV muon content are consistent with the predictions assuming recent composition models. Comparing the results to measurements of GeV muons in air showers reveals a tension in the obtained composition interpretation based on the post-LHC models.

We introduce a model for Non-Standard neutral current Interaction (NSI) between neutrinos and the matter fields, with an arbitrary coupling to the up and down quarks. The model is based on a new $U(1)$ gauge symmetry with a light gauge boson that mixes with the photon. We show that the couplings to the $u$ and $d$ quarks can have a ratio such that the contribution from NSI to the Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) amplitude vanishes, relaxing the bound on the NSI from the CE$\nu$NS experiments. Additionally, the deviation of the measured value of the anomalous magnetic dipole moment of the muon from the standard-model prediction can be fitted. The most limiting constraints on our model come from the search for the decay of the new gauge boson to $e^-e^+$ and invisible particles, carried out by NA48/2 and NA64, respectively. We show that these bounds can be relaxed by opening up the decay of the new gauge boson to new light scalars that eventually decay into the $e^- e^+$ pairs. We show that there are ranges that can lead to both a solution to the $(g - 2)_\mu$ anomaly and values of $\epsilon_{\mu \mu} = \epsilon_{\tau \tau}$ large enough to be probed by future solar neutrino experiments.

In the standard picture of galactic cosmic rays, a diffuse flux of high-energy gamma-rays and neutrinos is produced from inelastic collisions of cosmic ray nuclei with the interstellar gas. The neutrino flux is a guaranteed signal for high-energy neutrino observatories such as IceCube, but has not been found yet. Experimental searches for this flux constitute an important test of the standard picture of galactic cosmic rays. Both the observation and non-observation would allow important implications for the physics of cosmic ray acceleration and transport. We present CRINGE, a new model of galactic diffuse high-energy gamma-rays and neutrinos, fitted to recent cosmic ray data from AMS-02, DAMPE, IceTop as well as KASCADE. We quantify the uncertainties for the predicted emission from the cosmic ray model, but also from the choice of source distribution, gas maps and cross-sections. We consider the possibility of a contribution from unresolved sources. Our model predictions exhibit significant deviations from older models. Our fiducial model is available at https://doi.org/10.5281/zenodo.7373010 .

The observation of coherent elastic neutrino nucleus scattering has opened the window to many physics opportunities. This process has been measured by the COHERENT Collaboration using two different targets, first CsI and then argon. Recently, the COHERENT Collaboration has updated the CsI data analysis with a higher statistics and an improved understanding of systematics. Here we perform a detailed statistical analysis of the full CsI data and combine it with the previous argon result. We discuss a vast array of implications, from tests of the Standard Model to new physics probes. In our analyses we take into account experimental uncertainties associated to the efficiency as well as the timing distribution of neutrino fluxes, making our results rather robust. In particular, we update previous measurements of the weak mixing angle and the neutron root mean square charge radius for CsI and argon. We also update the constraints on new physics scenarios including neutrino nonstandard interactions and the most general case of neutrino generalized interactions, as well as the possibility of light mediators. Finally, constraints on neutrino electromagnetic properties are also examined, including the conversion to sterile neutrino states. In many cases, the inclusion of the recent CsI data leads to a dramatic improvement of bounds.

After the landmark discovery of non-zero $θ_{13}$ by the modern reactor experiments, unprecedented precision on neutrino mass-mixing parameters has been achieved over the past decade. This has set the stage for the discovery of leptonic CP violation (LCPV) at high confidence level in the next-generation long-baseline neutrino oscillation experiments. In this work, we explore in detail the possible complementarity among the on-axis DUNE and off-axis T2HK experiments to enhance the sensitivity to LCPV suppressing the $θ_{23}-δ_{\mathrm{CP}}$ degeneracy. We find that none of these experiments individually can achieve the milestone of 3$σ$ LCPV for at least 75% choices of $δ_{\mathrm{CP}}$ in its entire range of $[-180^{\circ} , 180^{\circ}]$, with their nominal exposures and systematic uncertainties. However, their combination can attain the same for all values of $θ_{23}$ with only half of their nominal exposures. We observe that the proposed T2HKK setup in combination with DUNE can further increase the CP coverage to more than 80% with only half of their nominal exposures. We study in detail how the coverage in $δ_{\mathrm{CP}}$ for $\ge$ 3$σ$ LCPV depends on the choice of $θ_{23}$, exposure, optimal runtime in neutrino and antineutrino modes, and systematic uncertainties in these experiments in isolation and combination. We find that with an improved systematic uncertainty of 2.7% in appearance mode, the standalone T2HK setup can provide a CP coverage of around 75% for all values of $θ_{23}$. We also discuss the pivotal role of intrinsic, extrinsic, and total CP asymmetries in the appearance channel and extrinsic CP asymmetries in the disappearance channel while analyzing our results.

Deviations from unitarity in the three-neutrino mixing canonical picture are expected in many physics scenarios beyond the Standard Model. The mixing of new heavy neutral leptons with the three light neutrinos would in principle modify the strength and flavour structure of charged-current and neutral-current interactions with matter. Non-unitarity effects would therefore have an impact on the neutrino decoupling processes in the early Universe and on the value of the effective number of neutrinos, $N_{\rm eff}$. We calculate the cosmological energy density in the form of radiation with a non-unitary neutrino mixing matrix, addressing the possible interplay between parameters. Highly accurate measurements of $N_{\rm eff}$ from forthcoming cosmological observations can provide independent and complementary limits on the departures from unitarity. For completeness, we relate the scenario of small deviations from unitarity to non-standard neutrino interactions and compare the forecasted constraints to other existing limits in the literature.

A sizable magnetic moment for neutrinos would be evidence of exotic physics. In the early Universe, left-handed neutrinos with a magnetic moment would interact with electromagnetic fields in the primordial plasma, flipping their helicity and producing a population of right-handed (RH) neutrinos. In this work, we present a new calculation of the production rate of RH neutrinos in a multi-component primordial plasma and quantify their contribution to the total energy density of relativistic species at early times, stressing the implications of the dependence on the initial time for production. Our results improve the previous cosmological limits by almost two orders of magnitudes. Prospects for upcoming cosmological experiments are also discussed.

We report three searches for high energy neutrino emission from astrophysical objects using data recorded with IceCube between 2011 and 2020. Improvements over previous work include new neutrino reconstruction and data calibration methods. In one search, the positions of 110 a priori selected gamma-ray sources were analyzed individually for a possible surplus of neutrinos over atmospheric and cosmic background expectations. We found an excess of $79_{-20}^{+22}$ neutrinos associated with the nearby active galaxy NGC 1068 at a significance of 4.2$\,\sigma$. The excess, which is spatially consistent with the direction of the strongest clustering of neutrinos in the Northern Sky, is interpreted as direct evidence of TeV neutrino emission from a nearby active galaxy. The inferred flux exceeds the potential TeV gamma-ray flux by at least one order of magnitude.

In the presence of extra neutrino states at high scales, the low-energy effective $3\times 3$ leptonic mixing matrix (LMM) is in general non-unitary. We revisit the question of what is our current knowledge of individual LMM matrix elements without assuming unitarity. We define two minimal sets of experimental constraints -- direct $+$ inherent bounds and indirect bounds, and analyze the implications of each set on leptonic non-unitarity. In addition, we clarify the treatment of flux and cross-section predictions, taking into account NP contamination in hadronic inputs. We use the currently running FASER$\nu$ experiment as a case study in order to demonstrate the sensitivity of collider neutrino experiments to leptonic non-unitarity. We find that indirect bounds constrain LMM non-unitarity to below the $10^{-3}$ level, stronger than current CKM non-unitarity constraints. Conversely, considering only direct and inherent bounds we find that ${\cal O}(1)$ unitarity violation is viable at $2\sigma$, and will be probed by the FASER$\nu$ experiment in the current run of the LHC.

We report on the first observation of the diffuse cosmic neutrino flux with the Baikal-GVD neutrino telescope. Using cascade-like events collected by Baikal-GVD in 2018--2021, a significant excess of events over the expected atmospheric background is observed. This excess is consistent with the high-energy diffuse cosmic neutrino flux observed by IceCube. The null cosmic flux assumption is rejected with a significance of 3.05$\sigma$. Assuming a single power law model of the astrophysical neutrino flux with identical contribution from each neutrino flavor, the following best-fit parameter values are found: the spectral index $\gamma_{astro}$ = $2.58^{+0.27}_{-0.33}$ and the flux normalization $\phi_{astro}$ = 3.04$^{+1.52}_{-1.21}$ per one flavor at 100 TeV.

It is still unknown whether the mass terms for neutrinos are of Majorana type or of Dirac type. An interesting possibility, known as pseudo-Dirac scheme combines these two with a dominant Dirac mass term and a subdominant Majorana one. As a result, the mass eigenstates come in pairs with a maximal mixing and a small splitting determined by the Majorana mass. This will affect the neutrino oscillation pattern for long baselines. We revisit this scenario employing recent solar neutrino data, including the seasonal variation of the $^7$Be flux recently reported by BOREXINO. We constrain the splitting using these data and find that both the time integrated solar neutrino data and the seasonal variation independently point towards a new pseudo-Dirac solution with nonzero splitting for $\nu_2$ of $\Delta m_2^2\simeq 1.5\times 10^{-11}$ eV$^2$. We propose alternative methods to test this new solution. In particular, we point out the importance of measuring the solar neutrino flux at the intermediate energies $1.5~{\rm MeV}

Extreme conditions present in the interiors of the core-collapse supernovae make neutrino-neutrino interactions not only feasible but dominant in specific regions, leading to the non-linear evolution of the neutrino flavor. Results obtained when such collective neutrino oscillations are treated in the mean-field approximation deviate from the results using the many-body picture because of the ignored quantum correlations. We present the first three flavor many-body calculations of the collective neutrino oscillations. The entanglement is quantified in terms of the entanglement entropy and the components of the polarization vector. We propose a qualitative measure of entanglement in terms of flavor-lepton number conserved quantities. We find that in the cases considered in the present work, the entanglement can be underestimated in two flavor approximation. The dependence of the entanglement on mass ordering is also investigated. We also explore the mixing of mass eigenstates in different mass orderings.

Ultralight axion-like particles $m_a \sim 10^{-22}$ eV, or Fuzzy Dark Matter (FDM), behave comparably to cold dark matter (CDM) on cosmological scales and exhibit a kpc-size de Broglie wavelength capable of alleviating established (sub-)galactic-scale problems of CDM. Substructures inside an FDM halo incur gravitational potential perturbations, resulting in stellar heating sufficient to account for the Galactic disc thickening over a Hubble time, as first demonstrated by Church et al. We present a more sophisticated treatment that incorporates the full baryon and dark matter distributions of the Milky Way and adopts stellar disc kinematics inferred from recent Gaia, APOGEE, and LAMOST surveys. Ubiquitous density granulation and subhalo passages respectively drive inner disc thickening and flaring of the outer disc, resulting in an observationally consistent `U-shaped' disc vertical velocity dispersion profile with the global minimum located near the solar radius. The observed age-velocity dispersion relation in the solar vicinity can be explained by the FDM-substructure-induced heating and places an exclusion bound $m_a \gtrsim 0.4\times10^{-22}$ eV. We assess non-trivial uncertainties in the empirical core-halo relation, FDM subhalo mass function and tidal stripping, and stellar heating estimate. The mass range $m_a\simeq 0.5-0.7\times10^{-22}$ eV favoured by the observed thick disc kinematics is in tension with several exclusion bounds inferred from dwarf density profiles, stellar streams, and Milky Way satellite populations, which could be significantly relaxed due to the aforesaid uncertainties. Additionally, strongly anisotropic heating could help explain the formation of ultra-thin disc galaxies.

Tests of models for new physics appearing in neutrino experiments often involve global fits to a quantum mechanical effect called neutrino oscillations. This paper introduces students to methods commonly used in these global fits starting from an understanding of more conventional fitting methods using log-likelihood and $\chi^2$ minimization. Specifically, we discuss how the $\Delta\chi^2$, which compares the $\chi^2$ of the fit with the new physics to the $\chi^2$ of the Standard Model prediction, is often interpreted using Wilks's theorem. This paper uses toy models to explore the properties of $\Delta\chi^2$ as a test statistic for oscillating functions. The statistics of such models are shown to deviate from Wilks's theorem. Tests for new physics also often examine data subsets for ``tension'' called the ``parameter goodness of fit''. In this paper, we explain this approach and use toy models to examine the validity of the probabilities from this test also. Although we have chosen a specific scenario -- neutrino oscillations -- to illustrate important points, students should keep in mind that these points are widely applicable when fitting multiple data sets to complex functions.

We study the impact of the dynamical Lorentz symmetry breaking induced by the auxiliary gauge fields of neutrino on the oscillations probability at DUNE. The DLSB introduces an alternative energy-momentum relation of the neutrinos and thus results in a new oscillation probability. We extend the previously proposed four-Majorana fermion model that gives rise to DLSB after the type II seesaw mechanism by considering the electron neutrino forward scattering when passing through a medium. Moreover, we incorporate the three-flavor neutrino states, which introduce the CP-violation term inside the oscillation probability. The impact of DLSB parameters around the order of $10^{-2}-10^{-3}$, which are at a strong coupling regime, on the oscillation probability is found to be measurable at DUNE within the 20 years through $\nu_e$ and $\overline{\nu}_e$ disappearance signals. We also compare the predicted spectra of the DLSB oscillations and the oscillation with the CP-violating term equal to $\pi/2$ to conclude that the presence of DLSB would increase the systematic uncertainty for the measurement of CP-violation at DUNE.

This paper describes a new $\nu_e$ identification method specifically designed to improve the low-energy ($< 30\,\mathrm{GeV}$) $\nu_e$ identification efficiency attained by enlarging the emulsion film scanning volume with the next generation emulsion readout system. A relative increase of 25-70% in the $\nu_e$ low-energy region is expected, leading to improvements in the OPERA sensitivity to neutrino oscillations in the framework of the 3 + 1 model. The method is applied to a subset of data where the detection efficiency increase is expected to be more relevant, and one additional $\nu_e$ candidate is found. The analysis combined with the $\nu_\tau$ appearance results improves the upper limit on $\sin^2 2\theta_{\mu e}$ to 0.016 at 90% C.L. in the MiniBooNE allowed region $\Delta m^2_{41} \sim 0.3\,\mathrm{eV}^2$.

While supermassive black hole masses have been cataloged across cosmic time, only a few dozen of them have robust spin measurements. By extending and improving the existing Event Horizon Telescope (EHT) array, the next-generation Event Horizon Telescope (ngEHT) will enable multifrequency, polarimetric movies on event horizon scales, which will place new constraints on the space-time and accretion flow. By combining this information, it is anticipated that the ngEHT may be able to measure tens of supermassive black hole masses and spins. In this white paper, we discuss existing spin measurements and many proposed techniques with which the ngEHT could potentially measure spins of target supermassive black holes. Spins measured by the ngEHT would represent a completely new sample of sources that, unlike pre-existing samples, would not be biased towards objects with high accretion rates. Such a sample would provide new insights into the accretion, feedback, and cosmic assembly of supermassive black holes.

The Sun emits copious amounts of photons and neutrinos in an approximately spatially isotropic distribution. Diffuse $γ$-rays and ultra-high energy (UHE) neutrinos from extragalactic sources may subsequently interact and annihilate with the emitted solar photons and neutrinos respectively. This will in turn induce an anisotropy in the cosmic ray (CR) background due to attenuation of the $γ$-ray and UHE neutrino flux by the solar radiation. Measuring this reduction, therefore, presents a simple and powerful astrophysical probe of electroweak interactions. In this letter we compute such anisotropies for TeV $γ$-rays, which at the Earth (Sun) can be at least $\simeq 10^{-4},(10^{-2})$. The optical depth at Earth for elongation angles more focused around the Sun ($\lesssim 10^\circ$), can be around $10^{-3}$ and larger. Neutrino attenuation is extremely tiny for for PeV scale UHE neutrinos. We briefly discuss observational prospects for experiments such as the Fermi Gamma-Ray Space Telescope Large Area Telescope (Fermi LAT), High-Altitude Water Cherenkov (HAWC) detector, The Large High Altitude Air Shower Observatory (LHAASO), Cherenkov Telescope Array (CTA) and IceCube. The potential for measuring $γ$-ray attenuation at orbital locations of other active satellites such as the Parker Solar Probe and James Webb Space Telescope (JWST) is also explored.

We analytically calculate the neutrino conversion probability $P_{\mu e}$ in the presence of sterile neutrinos, with exact dependence on $\Delta m^2_{41}$ and with matter effects explicitly included. Using perturbative expansion in small parameters, the terms involving the small mixing angles $\theta_{24}$ and $\theta_{34}$ can be separated out, with $\theta_{34}$ dependence only arising due to matter effects. We express $P_{\mu e}$ in terms of the quantities of the form $\sin(x)/x$, which helps in elucidating its dependence on matter effects and a wide range of $\Delta m^2_{41}$ values. Our analytic expressions allow us to predict the effects of the sign of $\Delta m^2_{41}$ at a long baseline experiment like DUNE. We numerically calculate the sensitivity of DUNE to the sterile mass ordering and find that this sensitivity can be significant in the range $|\Delta m^2_{41}| \sim (10^{-4} - 10^{-2})$ eV$^2$, for either mass ordering of active neutrinos. The dependence of this sensitivity on the value of $\Delta m^2_{41}$ for all mass ordering combinations can be explained by investigating the resonance-like terms appearing due to the interplay between the sterile sector and matter effects.

We analyze the expected sensitivity of current and near-future water(ice)-Cherenkov atmospheric neutrino experiments in the context of standard three-flavor neutrinos oscillations. In this first in-depth combined atmospheric neutrino analysis, we analyze the current shared systematic uncertainties arising from the shared flux and neutrino-water interactions. We then implement the systematic uncertainties of each experiment in detail and develop the atmospheric neutrino simulations for Super-Kamiokande (SK), with and without neutron-tagging capabilities (including SuperK-Gd), IceCube-Upgrade, and ORCA detectors. We carefully review the synergies and features of these experiments to examine the potential of a joint analysis of these atmospheric neutrino data in resolving the $\theta_{23}$ octant at 99\% C.L. and determining the neutrino mass ordering above 5$\sigma$ by 2030. Additionally, we assess the capability to constraint $\theta_{13}$ and the CP-violating phase ($\delta_{CP}$) in the leptonic sector independently from reactor and accelerator neutrino data, providing vital information for next-generation neutrino oscillation experiments such as DUNE and Hyper-Kamiokande.

This article reports global fits of short-baseline neutrino data to oscillation models involving light sterile neutrinos. In the commonly-used 3+1 plane wave model, there is a well-known 4.9$σ$ tension between data sets sensitive to appearance versus disappearance of neutrinos. We find that models that damp the oscillation prediction for the reactor data sets, especially at low energy, substantially improve the fits and reduce the tension. We consider two such scenarios. The first scenario introduces the quantum mechanical wavepacket effect that accounts for the source size in reactor experiments into the 3+1 model. We find that inclusion of the wavepacket effect greatly improves the overall fit compared to a 3$ν$ model by $Δχ^2/$DOF$=61.1/4$ ($7.1σ$ improvement) with best-fit $Δm^2=1.4$ eV$^2$ and wavepacket length of 67fm. The internal tension is reduced to 3.4$σ$. If reactor-data only is fit, then the wavepacket preferred length is 91 fm ($>20$ fm at 99\% CL). The second model introduces oscillations involving sterile flavor and allows the decay of the heaviest, mostly sterile mass state, $ν_4$. This model introduces a damping term similar to the wavepacket effect, but across all experiments. Compared to a three-neutrino fit, this has a $Δχ^2/$DOF$=60.6/4$ ($7σ$ improvement) with preferred $Δm^2=1.4$ eV$^2$ and decay $Γ= 0.35$ eV$^2$. The internal tension is reduced to 3.7$σ$. For many years, the reactor event rates have been observed to have structure that deviates from prediction. Community discussion has focused on an excess compared to prediction observed at 5 MeV; however, other deviations are apparent. This structure has $L$ dependence that is well-fit by the damped models. Before assuming this points to new physics, we urge closer examination of systematic effects that could lead to this $L$ dependence.

LHAASO collaboration detected photons with energy above 10 TeV from the most recent gamma-ray burst (GRB), GRB221009A. Given the redshift of this event, $z\sim 0.15$, photons of such energy are expected to interact with the diffuse extragalactic background light (EBL) well before reaching Earth. In this paper we provide a novel neutrino-related explanation of the most energetic 18 TeV event reported by LHAASO. We find that the minimal viable scenario involves both mixing and transition magnetic moment portal between light and sterile neutrinos. The production of sterile neutrinos occurs efficiently via mixing while the transition magnetic moment portal governs the decay rate in the parameter space where tree-level decays via mixing to non-photon final states are suppressed. Our explanation of this event, while being consistent with the terrestrial constraints, points to the non-standard cosmology.

The extraordinarily bright gamma-ray burst GRB 221009A was observed by a large number of observatories, from radio frequencies to gamma-rays. Of particular interest are the reported observations of photon-like air showers of very high energy: an 18 TeV event in LHAASO and a 251 TeV event at Carpet-2. Gamma rays at these energies are expected to be absorbed by pair-production events on background photons when travelling intergalactic distances. Several works have sought to explain the observations of these events, assuming they originate from GRB 221009A, by invoking axion-like particles (ALPs). We reconsider this scenario and account for astrophysical uncertainties due to poorly known magnetic fields and background photon densities. We find that, robustly, the ALP scenario cannot simultaneously account for an 18 TeV and a 251 TeV photon from GRB 221009A.

In this paper, we study the capability of different long-baseline experiment options at the KM3NeT facility i.e., P2O, Upgraded P2O and P2SO to probe the light sterile neutrino and compare their sensitivities with DUNE. The P2O option will have neutrinos from a 90 KW beam at Protvino to be detected at the ORCA detector, the Upgraded P2O will have neutrinos from the upgraded 450 KW beam to be detected at the ORCA detector and the option P2SO will have neutrinos from a 450 KW beam to be detected at the upgraded Super-ORCA detector. All these options will have a baseline around 2595 km. Our results show that the experiments at the KM3NeT (DUNE) would be more sensitive if the value of $\Delta m^2_{41}$ is around 10 (1) eV$^2$. Our results also show that the role of near detector is very important for the study of sterile neutrinos and addition of near detector improves the sensitivity as compared to only far detector for 3+1 scenario. Among the three options at KM3NeT, the sensitivity of P2O and upgraded P2O is limited and sensitivity of P2SO is either comparable or better than DUNE.

Cosmological constraints on the sum of the neutrino masses can be relaxed if the number density of active neutrinos is reduced compared to the standard scenario, while at the same time keeping the effective number of neutrino species $N_{\rm eff}\approx 3$ by introducing a new component of dark radiation. We discuss a UV complete model to realise this idea, which simultaneously provides neutrino masses via the seesaw mechanism. It is based on a $U(1)$ symmetry in the dark sector, which can be either gauged or global. In addition to heavy seesaw neutrinos, we need to introduce $\mathcal{O}(10)$ generations of massless sterile neutrinos providing the dark radiation. Then we can accommodate active neutrino masses with $\sum m_\nu \sim 1$ eV, in the sensitivity range of the KATRIN experiment. We discuss the phenomenology of the model and identify the allowed parameter space. We argue that the gauged version of the model is preferred, and in this case the typical energy scale of the model is in the 10 MeV to few GeV range.

We consider a mechanism which allows to decrease attenuation of high energy gamma ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy $m_N\sim0.1\,\mathrm{MeV}$ mostly sterile neutrino $N$ which mixes with active neutrinos. $N$'s are produced in GRB in $\pi$ and $K$ decays via mixing with $\nu_\mu$. They undergo the radiative decay $N\rightarrow \nu \gamma$ on the way to the Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy $\gamma$ events at $18\,\mathrm{TeV}$ and potentially $251\,\mathrm{TeV}$ can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of $N\rightarrow \nu \gamma$ is at least of the order 10%.

Because of the difficulty in detecting final state taus, the mixing parameter $|V_{\tau N}|^2$ for heavy neutrino $N$ is not well studied at current experiments, compared with other mixing parameters $|V_{e N}|^2$ and $|V_{\mu N}|^2$. In this paper, we focus on a challenging scenario where $N$ mixes with active neutrino of tau flavour only, i.e. $ |V_{\tau N}|^2 \neq 0 $ and $|V_{e N}|^2 = |V_{\mu N}|^2 = 0$. We derive current constraints on $|V_{\tau N}|^2$ from the rare $Z$-boson decay and electroweak precision data (EWPD). To forecast the future limits, we also investigate the signal $p p \to \tau^{\pm} \tau^{\pm} j j $ via a Majorana heavy neutrino at future proton-proton colliders. To suppress the background, both taus are required to decay leptonically into muons, leading to the final state containing two same sign muons, at least two jets plus moderate missing energy. The signal and relevant background processes are simulated at the HL-LHC and SppC/FCC-hh with center-of-mass energy of 14 TeV and 100 TeV. The preselection and multivariate analyses based on machine-learning are performed to reduce background. Limits on $|V_{\tau N}|^2$ are shown for heavy neutrino mass in the range 10-1000 GeV based on measurements from the rare $Z$-boson decay and EWPD, and searches at the HL-LHC and SppC/FCC-hh with integrated luminosities of 3 and 20 ab$^{-1}$.

We discuss implications that can be obtained by searches for neutrinos from the brightest gamma-ray burst, GRB 221009A. We derive constraints on GRB model parameters such as the cosmic-ray loading factor and dissipation radius, taking into account both neutrino spectra and effective areas. The results are strong enough to constrain proton acceleration near the photosphere, and we find that the single burst limits are comparable to those from stacking analysis. Quasithermal neutrinos from subphotospheres and ultrahigh-energy neutrinos from external shocks are not yet constrained. We show that GeV-TeV neutrinos originating from neutron collisions are detectable, and urge dedicated analysis on these neutrinos with DeepCore and IceCube as well as ORCA and KM3NeT.

Several experiments have been proposed in the recent years to study the nature of tau neutrinos, in particular aiming for a first observation of tau anti-neutrinos, more stringent upper limit on its anomalous magnetic moment as well as new constrains on the strange-quark content of the nucleon. We propose here a new low-cost neutrino experiment at the CERN North area, named NaNu (North Area NeUtrino), compatible with the realization of the future SHADOWS and HIKE experiments at the same experimental area.

We report the detection of a significant ionospheric disturbance in the D-region of Earth's ionosphere which was associated with the massive gamma-ray burst GRB 221009A that occurred on October 9 2022. We identified the disturbance over northern Europe - a result of the increased ionisation by X- and gamma-ray emission from the GRB - using very low frequency (VLF) radio waves as a probe of the D-region. These observations demonstrate that an extra-galactic GRB can have a significant impact on the terrestrial ionosphere and illustrates that the Earth's ionosphere can be used as a giant X- and gamma-ray detector. Indeed, these observations may provide insights into the impacts of GRBs on the ionospheres of planets in our solar system and beyond.

In view of the great interest in liquid argon neutrino detectors, the $^{40}$Ar($\gamma,\gamma'$)$^{40}$Ar$^{*}$ reaction was revisited to guide a calculation of the neutral current neutrino cross section at supernova energies. Using the nuclear resonance fluorescence technique with a monoenergetic, 99% linearly polarized photon beam, we report a three-fold increase in magnetic dipole strength at around 10 MeV in $^{40}$Ar. Based on shell-model calculations, and using the experimentally identified transitions, the neutral current neutrino cross sections for low-energy reactions on $^{40}$Ar are calculated.

Recently, several telescopes, including Swift-BAT, GBM, and LHAASO, have observed the ever highest-energy and long-duration gamma-rays from a gamma-ray burst named as GRB221009A (located at a red-shift of $z=0.151$) on October 9, 2022. Conventional understanding tells us that very high-energy photons produced at such a far distance suffer severe attenuation before reaching the Earth. We propose the existence of a sub-MeV to $O(10)$ MeV heavy neutrino with a transitional magnetic dipole moment, via which the heavy neutrino is produced at the GRB. It then travels a long distance to our galaxy and decays into a neutrino and a photon, which is observed. In such a way, the original high-energy photon produced at the GRB can survive long-distance attenuation.

Neutrino oscillation experiments have measured precisely the mass-squared differences of three neutrino mass eigenstates, and three leptonic mixing angles by utilizing both neutrino and anti-neutrino oscillations. The possible CPT violation may manifest itself in the difference of neutrino and anti-neutrino oscillation parameters, making these experiments promising tools for testing CPT invariance. We investigate empirically the sensitivity of the CPT test via the difference in mass-squared splittings ($\Delta m^2_{31} - \Delta \overline{m}^2_{31}$) and in leptonic mixing angles ($\sin^2\theta_{23} - \sin^2\overline{\theta}_{23}$) with the synergy of T2K-II, NO$\nu$A extension, and JUNO experiments. If the CPT symmetry is found to be conserved, the joint analysis of the three experiments will be able to establish limits of $|\Delta m^2_{31} - \Delta \overline{m}^2_{31}|$ < $5.3\times 10^{-3} \text{eV}^2$ and $|\sin^2\theta_{23} - \sin^2\overline{\theta}_{23}|$ < $0.10$ at 3$\sigma$ C. L. on the possible CPT violation. We find that with ($\Delta m^2_{31} - \Delta \overline{m}^2_{31}$), the dependence of the statistical significance on the relevant parameters to exclude the CPT conservation is marginal, and that, if the difference in the best-fit values of $\Delta m^2_{31}$ and $\Delta \overline{m}^2_{31}$ measured by MINOS(+) and NO$\nu$A persists as the true, the combined analysis will rule out the CPT conservation at 4$\sigma$ C. L.. With the ($\sin^2\theta_{23} - \sin^2\overline{\theta}_{23}$), the statistical significance to exclude CPT invariance depends strongly on the true value of $\theta_{23}(\overline{\theta}_{23})$. In case of maximal mixing of $\theta_{23}$, the CPT conservation will be excluded at 3$\sigma$ C. L. or more if the difference in the best-fit values of $\theta_{23}$ and $\overline{\theta}_{23}$ remains as the true.

Neutrinos associated with solar flares (solar-flare neutrinos) provide information on particle acceleration mechanisms during the impulsive phase of solar flares. We searched using the Super-Kamiokande detector for neutrinos from solar flares that occurred during solar cycles $23$ and $24$, including the largest solar flare (X28.0) on November 4th, 2003. In order to minimize the background rate we searched for neutrino interactions within narrow time windows coincident with $\gamma$-rays and soft X-rays recorded by satellites. In addition, we performed the first attempt to search for solar-flare neutrinos from solar flares on the invisible side of the Sun by using the emission time of coronal mass ejections (CMEs). By selecting twenty powerful solar flares above X5.0 on the visible side and eight CMEs whose emission speed exceeds $2000$ $\mathrm{km \, s^{-1}}$ on the invisible side from 1996 to 2018, we found two (six) neutrino events coincident with solar flares occurring on the visible (invisible) side of the Sun, with a typical background rate of $0.10$ ($0.62$) events per flare in the MeV-GeV energy range. No significant solar-flare neutrino signal above the estimated background rate was observed. As a result we set the following upper limit on neutrino fluence at the Earth $\mathit{\Phi}<1.1\times10^{6}$ $\mathrm{cm^{-2}}$ at the $90\%$ confidence level for the largest solar flare. The resulting fluence limits allow us to constrain some of the theoretical models for solar-flare neutrino emission.

A major challenge of particle physics is determining the neutrino mass ordering (MO). Due to matter effects, the flavor content of the neutrino flux from a Core-Collapse Supernova (CCSN) depends on the true neutrino MO resulting in markedly different energy and angle distributions for the measured lepton in water Cherenkov neutrino detectors. In this article, those distributions are compared for eight different CCSN models and used to study how their differences affect the determination of the neutrino mass ordering. In all cases, the inferred neutrino mass ordering is found to be either correct or inconclusive, with no significant false positives. However, the substantial variation observed among model predictions emphasizes the criticality of ongoing research in CCSN modeling.

We developed a simple small-scale experiment to measure the beta decay spectrum of $^{3}$H. The aim of this research is to investigate the presence of sterile neutrinos in the keV region. Tritium nuclei were embedded in a 1$\times$1$\times$1 cm$^3$ LiF crystal from the $^6$Li(n,$\alpha$)$^3$H reaction. The energy of the beta electrons absorbed in the LiF crystal was measured with a magnetic microcalorimeter at 40 mK. We report a new method of sample preparation, experiments, and analysis of $^3$H beta measurements. The spectrum of a 10-hour measurement agrees well with the expected spectrum of $^3$H beta decay. The analysis results indicate that this method can be used to search for keV-scale sterile neutrinos.

We present a search for eV-scale sterile neutrino oscillations in the MicroBooNE liquid argon detector, simultaneously considering all possible appearance and disappearance effects within the $3+1$ active-to-sterile neutrino oscillation framework. We analyze the neutrino candidate events for the recent measurements of charged-current $\nu_e$ and $\nu_{\mu}$ interactions in the MicroBooNE detector, using data corresponding to an exposure of 6.37$\times$10$^{20}$ protons on target from the Fermilab booster neutrino beam. We observe no evidence of light sterile neutrino oscillations and derive exclusion contours at the $95\%$ confidence level in the plane of the mass-squared splitting $\Delta m^2_{41}$ and the sterile neutrino mixing angles $\theta_{\mu e}$ and $\theta_{ee}$, excluding part of the parameter space allowed by experimental anomalies. Cancellation of $\nu_e$ appearance and $\nu_e$ disappearance effects due to the full $3+1$ treatment of the analysis leads to a degeneracy when determining the oscillation parameters, which is discussed in this paper and will be addressed by future analyses.

We update and summarize the present status of our understanding of the reparametrization symmetry with $i \leftrightarrow j$ state exchange in neutrino oscillation in matter. We introduce a systematic method called ``Symmetry Finder'' (SF) to uncover such symmetries, demonstrate its efficient hunting capability, and examine their characteristic features. Apparently they have a local nature: The 1-2 and 1-3 state exchange symmetries exist at around the solar- and atmospheric-resonances, respectively, with the level-crossing states exchanged. However, this view is not supported, to date, in the globally valid Denton et al. (DMP) perturbation theory, which possesses the 1-2 exchange symmetry but not the 1-3. It is probably due to lack of our understanding, and we find a clue for a larger symmetry structure than that we know. In the latter part of this article, we introduce non-unitarity, or unitarity violation (UV), into the $\nu$SM neutrino paradigm, a low-energy description of beyond $\nu$SM new physics at high (or low) scale. Based on the analyses of UV extended versions of the atmospheric-resonance and the DMP perturbation theories, we argue that the reparametrization symmetry has a diagnostics capability for the theory with the $\nu$SM and UV sectors. A speculation is given on the topological nature of the identity which determines the transformation property of the UV $\alpha$ parameters.

Geoneutrinos are a unique tool that brings to the surface information about our planet, in particular, its radiogenic power, insights formation and chemical composition. To date, only the KamLAND and Borexino experiments observed geoneutrino, with the former characterized by low concentration of heat-producing elements in the Earth in contrast to the latter that sets tight upper limits on the power of a georeactor hypothesized. With respect to the results yielded therefrom, a small discrepancy has been identified. On this account, next generation experiments like JUNO are needed if it is to provide definitive results with respect to the Earth's radiogenic power, and to fully exploit geoneutrinos to better understand deep Earth. An accurate a priori prediction of the crustal contribution plays an important role in enabling the translation of a particle physics measurement into geo-scientific questions. The existing GIGJ model of JUNO only focused on constructing a geophysical model of the local crust, without local geochemical data. Another existing JULOC includes both data, but only able to be achieved for the top layer of the upper crust, not in deep vertical. This paper reports on the development of JUNO's first 3-D integrated model, JULOC-I, which combines seismic, gravity, rock sample and thermal flow data with new building method, solved the problem in vertical depth. JULOC-I results show higher than expected geoneutrino signals are mainly attributable to higher U and Th in southern China than that found elsewhere on Earth. Moreover, the high level of accuracy of the JULOC-I model, complemented by 10 years of experimental data, indicates that JUNO has an opportunity to test different mantle models. Predictions by JULOC-I can be tested after JUNO goes online and higher accuracy local crustal model continue to play an important role to improve mantle measurements precision.

CP phase determination for the near future long baseline experiments, T2HK and DUNE, will require precise measurements of the oscillation probabilities. However, the uncertainty in the Earth's density must be considered in determining these oscillation probabilities. Therefore, in this study, we update the individual sensitivities of these experiments for determining the current unknowns in the standard three flavor scenario considering the latest configuration and also the complementarity between them while considering the uncertainty in the density. Our study showed that this uncertainty has a non-negligible impact on the precision of the CP phase determination particularly for DUNE.

The physics potential of detecting $^8$B solar neutrinos is exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of $^{13}$C nuclei in the liquid-scintillator detectors and the potential low background level, $^8$B solar neutrinos would be observable in the CC and NC interactions on $^{13}$C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the $^8$B solar neutrino observation. From the sensitivity studies performed in this work, we show that one can reach the precision levels of 5%, 8% and 20% for the $^8$B neutrino flux, $\sin^2\theta_{12}$, and $\Delta m^2_{21}$, respectively, using ten years of JUNO data. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the $^8$B neutrino flux measurement.

Anomalies in past neutrino measurements have led to the discovery that these particles have non-zero mass and oscillate between their three flavors when they propagate. In the 2010's, similar anomalies observed in the antineutrino spectra emitted by nuclear reactors have triggered the hypothesis of the existence of a supplementary neutrino state that would be sterile i.e. not interacting via the weak interaction. The STEREO experiment was designed to study this scientific case that would potentially extend the Standard Model of Particle Physics. Here we present a complete study based on our full set of data with significantly improved sensitivity. Installed at the ILL (Institut Laue Langevin) research reactor, STEREO has accurately measured the antineutrino energy spectrum associated to the fission of 235U. This measurement confirms the anomalies whereas, thanks to the segmentation of the STEREO detector and its very short mean distance to the core (10~m), the same data reject the hypothesis of a light sterile neutrino. Such a direct measurement of the antineutrino energy spectrum suggests instead that biases in the nuclear experimental data used for the predictions are at the origin of the anomalies. Our result supports the neutrino content of the Standard Model and establishes a new reference for the 235U antineutrino energy spectrum. We anticipate that this result will allow to progress towards finer tests of the fundamental properties of neutrinos but also to benchmark models and nuclear data of interest for reactor physics and for observations of astrophysical or geo-neutrinos.

The observational data on ultrahigh energy cosmic rays (UHECR), in particular their mass composition, show strong indications for extremely hard spectra of individual mass groups of CR nuclei at Earth. In this work, we show that such hard spectra can be the result of the finite life-time of UHECR sources, if a few individual sources dominate the UHECR flux at the highest energies. In this case, time delays induced by deflections in the turbulent extragalactic magnetic field as well as from the diffusive or advective escape from the source environment can suppress low-energy CRs, leading to a steepening of the observed spectrum. Considering radio galaxies as the main source of UHECRs, we discuss the necessary conditions that few individual sources dominate over the total contribution from the bulk of sources that have been active in the past. We provide two proof-of-principle scenarios showing that for a turbulent extragalactic magnetic field with a strength $B$ and a coherence length $l_{\rm coh}$, the life-time of a source at a distance $d_{\rm src}$ should satisfy ${t_{\rm act} \sim \left( B/1\,\text{nG} \right)^2\,\left( d_{\rm src}/10\,\text{Mpc} \right)^2\,\left( l_{\rm coh}/1\,\text{Mpc} \right)\,\text{Myr}}$ to obtain the necessary hardening of the CR spectrum at Earth.

Solar evolutionary models are thus far unable to reproduce spectroscopic, helioseismic, and neutrino constraints consistently, resulting in the so-called solar modeling problem. In parallel, planet formation models predict that the evolving composition of the protosolar disk and, thus, of the gas accreted by the proto-Sun must have been variable. We show that solar evolutionary models that include a realistic planet formation scenario lead to an increased core metallicity of up to 5%, implying that accurate neutrino flux measurements are sensitive to the initial stages of the formation of the Solar System. Models with homogeneous accretion match neutrino constraints to no better than 2.7$\sigma$. In contrast, accretion with a variable composition due to planet formation processes, leading to metal-poor accretion of the last $\sim$4% of the young Sun's total mass, yields solar models within 1.3$\sigma$ of all neutrino constraints. We thus demonstrate that in addition to increased opacities at the base of the convective envelope, the formation history of the Solar System constitutes a key element in resolving the current crisis of solar models.

The Standard Model of particle physics is a $SU(3)_c\times SU(2)_L\times U(1)_Y$ gauge theory that can explain the strong, weak, and electromagnetic interactions between the particles. The gravitational interaction is described by Einstein's General Relativity theory which is a classical theory of gravity. These theories can explain all the four fundamental forces of nature with great level of accuracy. However, there are several theoretical and experimental motivations of studying physics beyond the Standard Model of particle physics and Einstein's General Relativity theory. Probing these new physics scenarios with ultralight particles has its own importance as they can be a promising candidates for dark matter that can evade the constraints from dark matter direct detection experiments and solve the small scale structure problems of the universe. In this paper, we have considered axions and gauge bosons as light particles and their possible searches through astrophysical observations. In particular, we obtain constraints on ultralight axions from orbital period loss of compact binary systems, gravitational light bending, and Shapiro time delay. We also derive constraints on ultralight gauge bosons from indirect evidence of gravitational waves, and perihelion precession of planets. Such type of observations can also constrain several particle physics models and are discussed.

It has been reported that the Large High Altitude Air Shower Observatory (LHAASO) observed very high energy photons from GRB 221009A, with the highest energy reaching 18~TeV. We find that observation of such high energy photons is quite nontrivial since extragalactic background light could absorb these photons severely and the flux is too weak to be observed. Therefore we discuss a potential mechanism for us to observe these photons, and suggest that Lorentz invariance violation induced threshold anomaly of the process \(\gamma\gamma\to e^-e^+\) provides a candidate to explain this phenomenon.

Beginning in 2016, the IceCube Neutrino Observatory has sent out alerts in real time containing the information of high-energy ($E \gtrsim 100$~TeV) neutrino candidate events with moderate-to-high ($\gtrsim 30$\%) probability of astrophysical origin. In this work, we use a recent catalog of such alert events, which, in addition to events announced in real-time, includes events that were identified retroactively, and covers the time period of 2011-2020. We also search for additional, lower-energy, neutrinos from the arrival directions of these IceCube alerts. We show how performing such an analysis can constrain the contribution of rare populations of cosmic neutrino sources to the diffuse astrophysical neutrino flux. After searching for neutrino emission coincident with these alert events on various timescales, we find no significant evidence of either minute-scale or day-scale transient neutrino emission or of steady neutrino emission in the direction of these alert events. This study also shows how numerous a population of neutrino sources has to be to account for the complete astrophysical neutrino flux. Assuming sources have the same luminosity, an $E^{-2.5}$ neutrino spectrum and number densities that follow star-formation rates, the population of sources has to be more numerous than $7\times 10^{-9}~\textrm{Mpc}^{-3}$. This number changes to $3\times 10^{-7}~\textrm{Mpc}^{-3}$ if number densities instead have no cosmic evolution.

We investigate the sensitivity of a large, underground LArTPC-based neutrino detector to dark matter in the Galactic Center annihilating into neutrinos. Such a detector could have the ability to resolve the direction of the electron in a neutrino scattering event, and thus to infer information about the source direction for individual neutrino events. We consider the improvements on the expected experimental sensitivity that this directional information would provide. Even without directional information, we find a DUNE-like LArTPC detector is capable of setting limits on dark matter annihilation to neutrinos for dark matter masses above 30 MeV that are competitive with or exceed current experimental reach. While currently-demonstrated angular resolution for low-energy electrons is insufficient to allow any significant increase in sensitivity, these techniques could benefit from improvements to algorithms and the additional spatial information provided by novel 3D charge imaging approaches. We consider the impact of such enhancements to the resolution for electron directionality, and find that where electron-scattering events can be distinguished from charged-current neutrino interactions, limits on dark matter annihilation in the mass range where solar neutrino backgrounds dominate ($\lesssim 15$ MeV) can be significantly improved using directional information, and would be competitive with existing limits using $40$ kton$\times$year of exposure.

Weakly interacting massive particles (WIMPs) can be captured by the Sun and annihilate in the core, which may result in production of kaons that can decay at rest into monoenergetic 236 MeV neutrinos. Several studies of detection of these neutrinos at DUNE have been carried out. It has been shown that if the WIMP mass is below 4 GeV, then they will evaporate prior to annihilation, suppressing the signal. Since Jupiter has a cooler core, WIMPs with masses in the 1-4 GeV range will not evaporate and can thus annihilate into monoenergetic neutrinos. We calculate the flux of these neutrinos near the surface of Jupiter and find that it is comparable to the flux at DUNE for masses above 4 GeV and substantially greater in the 1-4 GeV range. Of course, detecting these neutrinos would require a neutrino detector near Jupiter. Obviously, it will be many decades before such a detector can be built, but should direct detection experiments find a WIMP with a mass in the 1-4 GeV range, it may be one of the few ways to learn about the annihilation process. A liquid hydrogen time projection chamber might be able to get precise directional information and energy of these neutrinos (and hydrogen is plentiful in the vicinity of Jupiter). We speculate that such a detector could be placed on the far side of one of the tidally locked Amalthean moons; the moon itself would provide substantial background shielding and the surface would allow easier deployment of solar panels for power generation.

Accurate neutrino-nucleus interaction modeling is an essential requirement for the success of the accelerator-based neutrino program. As no satisfactory description of cross sections exists, experiments tune neutrino-nucleus interactions to data to mitigate mis-modeling. In this work, we study how the interplay between near detector tuning and cross section mis-modeling affects new physics searches. We perform a realistic simulation of neutrino events and closely follow NOvA's tuning, the first published of such procedures in a neutrino experiment. We analyze two illustrative new physics scenarios, sterile neutrinos and light neutrinophilic scalars, presenting the relevant experimental signatures and the sensitivity regions with and without tuning. While the tuning does not wash out sterile neutrino oscillation patterns, cross section mis-modeling can bias the experimental sensitivity. In the case of light neutrinophilic scalars, variations in cross section models completely dominate the sensitivity regardless of any tuning. Our findings reveal the critical need to improve our theoretical understanding of neutrino-nucleus interactions, and to estimate the impact of tuning on new physics searches. We urge neutrino experiments to follow NOvA's example and publish the details of their tuning procedure, and to develop strategies to more robustly account for cross section uncertainties, which will expand the scope of their physics program.

We derive purely gravitational constraints on dark matter and cosmic neutrino profiles in the solar system using asteroid (101955) Bennu. We focus on Bennu because of its extensive tracking data and high-fidelity trajectory modeling resulting from the OSIRIS-REx mission. We find that the local density of dark matter is bound by $\rho_{\rm DM}\lesssim 3.3\times 10^{-15}\;\rm kg/m^3 \simeq 6\times10^6\,\bar{\rho}_{\rm DM}$, in the vicinity of $\sim 1.1$ au (where $\bar{\rho}_{\rm DM}\simeq 0.3\;\rm GeV/cm^3$). We show that high-precision tracking data of solar system objects can constrain cosmic neutrino overdensities relative to the Standard Model prediction $\bar{n}_{\nu}$, at the level of $\eta\equiv n_\nu/\bar{n}_{\nu}\lesssim 1.7 \times 10^{11}(0.1 \;{\rm eV}/m_\nu)$ (Saturn), comparable to the existing bounds from KATRIN and other previous laboratory experiments (with $m_\nu$ the neutrino mass). These local bounds have interesting implications for existing and future direct-detection experiments. Our constraints apply to all dark matter candidates but are particularly meaningful for scenarios including solar halos, stellar basins, and axion miniclusters, which predict or allow overdensities in the solar system. Furthermore, introducing a DM-SM long-range fifth force with a strength $\tilde{\alpha}_D$ times stronger than gravity, Bennu can set a constraint on $\rho_{\rm DM}\lesssim \bar{\rho}_{\rm DM}\left(6 \times 10^6/\tilde{\alpha}_D\right)$. These constraints can be improved in the future as the accuracy of tracking data improves, observational arcs increase, and more missions visit asteroids.

The kinematics of the three body decay, with a modified energy-momentum relation of the particles due to a violation of Lorentz invariance, is presented in detail in the collinear approximation. The results are applied to the decay of superluminal neutrinos producing an electron-positron or a neutrino-antineutrino pair. Explicit expressions for the energy distributions, required for a study of the cascade of neutrinos produced in the propagation of superluminal neutrinos, are derived.

The existence of high-energy astrophysical neutrinos has been unambiguously demonstrated, but their sources remain elusive. IceCube reported an association of a 290-TeV neutrino with a gamma-ray flare of TXS 0506+056, an active galactic nucleus with a compact radio jet pointing to us. Later, radio blazars were shown to be associated with IceCube neutrino events with high statistical significance. These associations remained unconfirmed with the data of independent experiments. Here we report on the detection of a rare neutrino event with the estimated energy of 224 +- 75 TeV from the direction of TXS 0506+056 by the new Baikal-GVD neutrino telescope in April 2021 followed by a radio flare observed by RATAN-600. This event is the highest-energy cascade detected so far by Baikal-GVD from a direction below horizon. The result supports previous suggestions that radio blazars in general, and TXS 0506+056 in particular, are the sources of high-energy neutrinos, and opens up the cascade channel for the neutrino astronomy.

We investigate the prospects for measuring the coherent elastic neutrino-nucleus scattering of solar and supernova neutrinos in future NaI(Tl) dark matter detection experiments. Considering the reduced background and improved light yield of the recently developed NaI(Tl) crystals, more than 3$\sigma$ observation sensitivities of the supernova neutrino within the Milky Way are demonstrated. In the case of the solar neutrino, approximately 3 observations are marginal with a 1 ton NaI(Tl) experiment assuming an order of magnitude reduced background, five photoelectron thresholds, and 5-year data exposure.

It is possible that the strongest interactions between dark matter and the Standard Model occur via the neutrino sector. Unlike gamma rays and charged particles, neutrinos provide a unique avenue to probe for astrophysical sources of dark matter, since they arrive unimpeded and undeflected from their sources. Previously, we reported on annihilations of dark matter to neutrinos; here, we review constraints on the decay of dark matter into neutrinos over a range of dark matter masses from MeV to ZeV, compiling previously reported limits, exploring new electroweak corrections and computing constraints where none have been computed before. We examine the expected contributions to the neutrino flux at current and upcoming neutrino experiments as well as photons from electroweak emission expected at gamma-ray telescopes, leading to constraints on the dark matter decay lifetime, which ranges from $\tau \sim 1.2\times10^{21}$ s at 10 MeV to $1.5\times10^{29}$s at 1 PeV.

Next generation neutrino oscillation experiments are expected to measure the remaining oscillation parameters with very good precision. They will have unprecedented capabilities to search for new physics that modify oscillations. DUNE, with its broad band beam, good particle identification, and relatively high energies will provide an excellent environment to search for new physics. If deviations from the standard three-flavor oscillation picture are seen however, it is crucial to know which new physics scenario is found so that it can be verified elsewhere and theoretically understood. We investigate several benchmark new physics scenarios by looking at existing long-baseline accelerator neutrino data from NOvA and T2K and determine at what sensitivity DUNE can differentiate among them. We consider sterile neutrinos and both vector and scalar non-standard neutrino interactions, all with new complex phases, the latter of which could conceivably provide absolute neutrino mass scale information. We find that, in many interesting cases, DUNE will have good model discrimination. We also perform a new fit to NOvA and T2K data with scalar NSI.

Ultra-high-energy neutrinos serve as messengers of some of the highest energy astrophysical environments. Given that neutrinos are neutral and only interact via weak interactions, neutrinos can emerge from sources, traverse astronomical distances, and point back to their origins. Their weak interactions require large target volumes for neutrino detection. Using the Earth as a neutrino converter, terrestrial, sub-orbital, and satellite-based instruments are able to detect signals of neutrino-induced extensive air showers. In this paper, we describe the software code $\texttt{nuPyProp}$ that simulates tau neutrino and muon neutrino interactions in the Earth and predicts the spectrum of the $\tau$-lepton and muons that emerge. The $\texttt{nuPyProp}$ outputs are lookup tables of charged lepton exit probabilities and energies that can be used directly or as inputs to the $\texttt{nuSpaceSim}$ code designed to simulate optical and radio signals from extensive air showers induced by the emerging charged leptons. We describe the inputs to the code, demonstrate its flexibility and show selected results for $\tau$-lepton and muon exit probabilities and energy distributions. The $\texttt{nuPyProp}$ code is open source, available on Github.

As a free, intensive, rarely interactive and well directional messenger, solar neutrinos have been driving both solar physics and neutrino physics developments for more than half a century. Since more extensive and advanced neutrino experiments are under construction, being planned or proposed, we are striving toward an era of precise and comprehensive measurement of solar neutrinos in the next decades. In this article, we review recent theoretical and experimental progress achieved in solar neutrino physics. We present not only an introduction to neutrinos from the standard solar model and the standard flavor evolution, but also a compilation of a variety of new physics that could affect and hence be probed by solar neutrinos. After reviewing the latest techniques and issues involved in the measurement of solar neutrino spectra and background reduction, we provide our anticipation on the physics gains from the new generation of neutrino experiments.

The Galactic Center Gamma-Ray Excess has a spectrum, angular distribution, and overall intensity that agree remarkably well with that expected from annihilating dark matter particles in the form of a $m_X \sim 50 \, {\rm GeV}$ thermal relic. Previous claims that these photons are clustered on small angular scales or trace the distribution of known stellar populations once appeared to favor interpretations in which this signal originates from a large population of unresolved millisecond pulsars. More recent work, however, has overturned these conclusions, finding that the observed gamma-ray excess does {\it not} contain discernible small scale power, and is distributed with approximate spherical symmetry, not tracing any known stellar populations. In light of these results, it now appears significantly more likely that the Galactic Center Gamma-Ray Excess is produced by annihilating dark matter.

Compared to other neutrino sources, the huge anti-neutrino fluxes at nuclear reactor based experiments empower us to derive stronger bounds on non-standard interactions of neutrinos with electrons mediated by light scalar/vector mediators. At neutrino energy around $200$~keV reactor anti-neutrino flux is at least an order of magnitude larger compared to the solar flux. The atomic and crystal form factors of the detector materials related to the details of the atomic structure becomes relevant at this energy scale as the momentum transfers would be small. Non-standard neutrino-electron interaction mediated by light scalar/vector mediator arises naturally in many low-scale models. We also propose one such new model with a light scalar mediator. Here, we investigate the parameter space of such low-scale models in reactor based neutrino experiments with low threshold Ge and Si detectors, and find the prospect of probing/ruling out the relevant parameter space by finding the projected sensitivity at $90 \%$ confidence level by performing a $\chi^2$-analysis. We find that a detector capable of discriminating between electron recoil and nuclear recoil signal down to a very low threshold such as $5$~eV placed in reactor based experiment would be able to probe a larger region in parameter space compared to the previously explored region. A Ge (Si) detector with $10$~kg-yr exposure and 1 MW reactor anti-neutrino flux would be able to probe the scalar and vector mediators with masses below 1 keV for coupling products $\sqrt{g_\nu g_e}$ $\sim$ $1 \times 10^{-6}~(9.5 \times 10^{-7})$ and $1\times 10^{-7} ~(8\times 10^{-8})$, respectively.

We revisit the possibility that neutrinos undergo non-radiative decay. We investigate the potential to extract information on the neutrino lifetime-to-mass ratio from the diffuse supernova neutrino background. To this aim, we explicitly consider the current uncertainties on the core-collapse supernova rate and the fraction of failed supernovae. We present predictions in a full 3 neutrino framework in the absence and presence of neutrino non-radiative decay, for the Super-Kamiokande+Gd, the JUNO, the Hyper-Kamiokande, and the DUNE experiments, that should observe the diffuse supernova neutrino background in the near future. Our results show the importance of a 3 neutrino treatment of neutrino decay and of identifying the neutrino mass ordering to break possible degeneracies between DSNB predictions in the presence of decay and standard physics.

Majoron-like bosons would emerge from a supernova (SN) core by neutrino coalescence of the form $\nu\nu\to\phi$ and $\bar\nu\bar\nu\to\phi$ with 100 MeV-range energies. Subsequent decays to (anti)neutrinos of all flavors provide a flux component with energies much larger than the usual flux from the "neutrino sphere." The absence of 100 MeV-range events in the Kamiokande-II and Irvine-Michigan-Brookhaven signal of SN 1987A implies that less than 1% of the total energy was thus emitted and provides the strongest constraint on the Majoron-neutrino coupling of $g\lesssim 10^{-9}\,{\rm MeV}/m_\phi$ for $100~{\rm eV}\lesssim m_\phi\lesssim 100~{\rm MeV}$. It is straightforward to extend our new argument to other hypothetical feebly interacting particles.

A new measurement of elastic $pp$ scattering at $\sqrt{s} = 13$ TeV with the ATLAS-ALFA detector is presented. The measurement was performed using data recorded in a special run of the LHC with $\beta^\star = 2.5$ km. The elastic cross-section was measured differentially in the Mandelstam $t$ variable and from a fit to ${\textrm{d}}\sigma/\textrm{d}t$ the total cross section, the $\rho$-parameter and parameters of the nuclear slope are determined. The results for $\sigma_{\textrm{tot}}$ and $\rho$ are \begin{equation*} \sigma_{\textrm{tot}}(pp\rightarrow X) = \mbox{104.7} \; \pm 1.1 \; \mbox{mb} , \; \; \rho = \mbox{0.098} \; \pm 0.011 . \end{equation*} The energy evolution of $\sigma_{\textrm{tot}}$ and $\rho$, connected through dispersion relations, is compared to several models. Furthermore, the total inelastic cross section is determined from the difference of the total and elastic cross section, and the ratio of the elastic to total cross section is calculated.

Neutrino flavour oscillation is one of the primary indication of the existence of new physics beyond standard model. The presence of small neutrino mass is indispensable to explicate the oscillation among different flavours of neutrino. By the addition of a right handed neutral lepton with the standard model fermions, it is possible to generate tiny neutrino mass. Such additional fermion may induce non-unitarity to the $3\times 3$ PMNS mixing matrix which influences the propagation of neutrino in space-time. In this work the effect of non-unitary mixing matrix is analyzed in neutrino oscillation in presence of two new physics scenarios, Lorentz violation and dark non-standard interaction. Lorentz symmetry violation mainly appears at the Planck scale, which may also be manifested at a lower energy level. On the other hand, dark non standard interaction arises due to the interaction of neutrino with the environmental dark matter which contributes as a perturbative correction to the neutrino mass. In this analysis, the comparative study of unitary and non-unitary mixing matrix is carried out considering the scenario of Lorentz violation and dark NSI in the context of long baseline DUNE and short baseline Daya Bay experimental set up. The signature of dark nonstandard interaction is observable in both DUNE and Daya Bay set up in terms of large value of neutrino survival and oscillation probability respectively and is a possible explanation for the excess flux observed at $\sim5$ MeV in Daya Bay experiment. The signature of Lorentz violation is also possible to be observed in the short baseline Daya Bay experiment only.

A Galactic cosmic-ray transport model featuring non-homogeneous transport has been developed over the latest years. This setup is aimed at reproducing gamma-ray observations in different regions of the Galaxy (with particular focus on the progressive hardening of the hadronic spectrum in the inner Galaxy) and was shown to be compatible with the very-high-energy gamma-ray diffuse emission recently detected up to PeV energies. In this work, we extend the results previously presented to test the reliability of that model throughout the whole sky. To this aim, we compare our predictions with detailed longitude and latitude profiles of the diffuse gamma-ray emission measured by Fermi-LAT for different energies and compute the expected Galactic neutrino diffuse emission, comparing it with current limits from the ANTARES collaboration. We emphasize that the possible detection of a Galactic neutrino component will allow us to break the degeneracy between our model and other scenarios featuring prominent contributions from unresolved sources and TeV halos.

Dark matter (DM) can be captured in celestial bodies after scattering and losing sufficient energy to become gravitationally bound. We derive a general framework that describes the current DM distribution inside celestial objects, which self-consistently includes the effects of concentration diffusion, thermal diffusion, gravity, and capture accumulation. For DM with sufficient interactions, we show that a significant DM population can thermalize and sit towards the celestial-body surface. This floating distribution allows for new phenomenology for DM searches in a wide range of celestial bodies, including the Sun, Earth, Jupiter, Brown Dwarfs, and Exoplanets.

The Standard Model predicts a long-range force, proportional to $G_F^2/r^5$, between fermions due to the exchange of a pair of neutrinos. This quantum force is feeble and has not been observed yet. In this paper, we compute this force in the presence of neutrino backgrounds, both for isotropic and directional background neutrinos. We find that for the case of directional background the force can have a $1/r$ dependence and it can be significantly enhanced compared to the vacuum case. In particular, background effects caused by reactor, solar, and supernova neutrinos enhance the force by many orders of magnitude. The enhancement, however, occurs only in the direction parallel to the direction of the background neutrinos. We discuss the experimental prospects of detecting the neutrino force in neutrino backgrounds and find that the effect is close to the available sensitivity of the current fifth force experiments. Yet, the angular spread of the neutrino flux and that of the test masses reduce the strength of this force. The results are encouraging and a detailed experimental study is called for to check if the effect can be probed.

The flux of high energy neutrinos and photons produced in a blazar could get attenuated when they propagate through the dark matter spike around the central black hole and the halo of the host galaxy. Using the observation by IceCube of a few high-energy neutrino events from TXS 0506+056, and their coincident gamma ray events, we obtain new constraints on the dark matter-neutrino and dark matter-photon scattering cross sections. Our constraints are orders of magnitude more stringent than those derived from considering the attenuation through the intergalactic medium and the Milky Way dark matter halo. When the cross-section increases with energy, our constraints are also stronger than those derived from the CMB and large-scale structure.

The next generation of radio telescopes will be sensitive to low-scale quantum gravity by measuring ultra-high-energy neutrinos. In this letter, we demonstrate for the first time that neutrino-nucleon soft interactions induced by TeV-scale gravity would significantly increase the number of events detected by the IceCube-Gen2 radio array in the EeV regime. However, we show that these experiments cannot measure the total cross section using only the angular and energy information of the neutrino flux, unless assumptions on the underlying inelasticity distribution of neutral interactions are made.

The Non-Standard Interactions (NSIs) are subdominant effects, often appearing in various extensions of SM, which may impact the neutrino oscillations through matter. It is important and interesting to explore the impact of NSIs in the ongoing and upcoming precise neutrino oscillations experiments. In this work, we have studied the imprints of a scalar-mediated NSI in three upcoming long-baseline (LBL) experiments (DUNE, T2HK, T2HKK). The effects of scalar NSI appears as a medium-dependent correction to the neutrino mass term. Its contribution scales linearly with matter density, making LBL experiments a suitable candidate to probe its effects. We show that the scalar NSI may significantly impact the oscillation probabilities, event rates at the detectors and the $\chi^2$-sensitivities of $\delta_{CP}$ measurements. We present the results of a combined analysis involving the LBL experiments (DUNE+T2HK, DUNE+T2HKK, DUNE+T2HK+T2HKK) which offer a better capability of constraining the scalar NSI parameters as well as an improved sensitivity towards CP-violation.

Massive neutrinos are guaranteed to have nonzero electromagnetic moments and, since there are at least three neutrino species, these dipole moments define a matrix. Here, we estimate the current upper bounds on all independent neutrino electromagnetic moments, concentrating on Earth-bound experiments and measurements with solar neutrinos, including the very recent results reported by XENONnT. We make no simplifying assumptions and compare the hypotheses that neutrinos are Majorana fermions or Dirac fermions. In particular, we fully explore constraints in the Dirac-neutrino parameter space. Majorana and Dirac neutrinos are different; for example, the upper bounds on the magnitudes of the elements of the dipole moment matrix are weaker for Dirac neutrinos, relative to Majorana neutrinos. The potential physics reach of next-generation experiments also depends on the nature of the neutrino. We find that a next-generation experiment two orders of magnitude more sensitive to the neutrino electromagnetic moments via $\nu_{\mu}$ elastic scattering may discover that the neutrino electromagnetic moments are nonzero if the neutrinos are Dirac fermions. Instead, if the neutrinos are Majorana fermions, such a discovery is ruled out by existing solar neutrino data, unless there are more than three light neutrinos.

We study the online detection by gallium capture of mono-energetic neutrinos produced by a $^{51}$Cr radioactive source in a scintillation experiment. We find that cerium-doped gadolinium aluminum gallium garnet (GAGG) is a suitable scintillator which contains about 21% of gallium per weight and has a high mass density and light yield. Combined with a highly efficient light detection system this allows tagging of the subsequent germanium decay and thus a clean distinction of gallium capture and elastic neutrino electron scattering events. With 1.5 tons of scintillator and 10 source runs of 3.4MCi, each, we obtain about 760 gallium capture events with a purity of 85% and 680,000 neutrino electron scattering events, where the latter provide a precise normalization independent of any nuclear physics. This configuration would allow to test the gallium anomaly at more than $5\sigma$ in an independent way.

Neutrino emission in coincidence with gamma rays has been observed from the blazar TXS 0506+056 by the IceCube telescope. Neutrinos from the blazar had to pass through a dense spike of dark matter (DM) surrounding the central black hole. The observation of such a neutrino implies new upper bounds on the neutrino-DM scattering cross section as a function of DM mass. The constraint is stronger than existing ones for a range of DM masses, if the cross section rises linearly with energy. For constant cross sections, competitive bounds are also possible, depending on details of the DM spike.

The significance of the Gallium Anomaly, from the BEST, GALLEX, and SAGE radioactive source experiments, is quantified using different theoretical calculations of the neutrino detection cross section, and its explanation due to neutrino oscillations is compared with the bounds from the analyses of reactor rate and spectral ratio data, $\beta$-decay data, and solar neutrino data. In the 3+1 active-sterile neutrino mixing scheme, the Gallium Anomaly is in strong tension with the individual and combined bounds of these data sets. In the combined scenario with all available data, the parameter goodness of fit is below 0.042%, corresponding to a severe tension of 4-5$\sigma$, or stronger. Therefore, we conclude that one should pursue other possible solutions beyond short-baseline oscillations for the Gallium Anomaly. We also present a new global fit of $\nu_e$ and $\bar\nu_e$ disappearance data, showing that there is a 2.6-3.3$\sigma$ preference in favor of short-baseline oscillations, which is driven by an updated analysis of reactor spectral ratio data.

We point out three apparent inconsistencies in the treatment of oscillation coherence from reactor neutrino and source neutrino experiments in recent paper "Damping of neutrino oscillations, decoherence and the lengths of neutrino wave packets''. First, that the dependence of the oscillation probability upon the subsequent interactions of entangled recoil particles implies causality violations and in some situations superluminal signaling; second, that integrating over a non-orthogonal basis for the entangled recoil leads to unphysical effects; and third, that the question of what interactions serve to measure the position of the initial state particle remains ambiguous. These points taken together appear to undermine the claim made therein that the effects of wave packet separation must be strictly unobservable in reactor and radioactive source based neutrino experiments.

In this paper we explore interactions between neutrinos and Dark Matter. In particular, we study how the propagation of astrophysical neutrinos can be modified by computing the most general potential generated by the galactic DM background. We use on-shell techniques to compute this potential in a completely model independent way and obtain an expression valid for any Dark Matter mass and spin. Afterwards, we use this expression to analyse under what circumstances such potential can be important at the phenomenological level, and we find that under some assumptions only ultra light scalar Dark Matter could be of any relevance to oscillation experiments.

Several neutrino experiments have reported results that are potentially inconsistent with our current understanding of the lepton sector. A candidate solution to these so-called short-baseline anomalies is postulating the existence of new, eV-scale, mostly sterile neutrinos that mix with the active neutrinos. This hypothesis, however, is strongly disfavored once one considers all neutrino data, especially those that constrain the disappearance of muon and electron neutrinos at short-baselines. Here, we show that if the sterile-active mixing parameters depend on the energy-scales that characterize neutrino production and detection, the sterile-neutrino hypothesis may provide a reasonable fit to all neutrino data. The reason for the improved fit is that the stringent disappearance constraints on the different elements of the extended neutrino mixing matrix are associated to production and detection energy scales that are different from those that characterize the anomalous LSND and MiniBooNE appearance data. We show, via a concrete example, that secret interactions among the sterile neutrinos can lead to the results of interest.

The centers of the core-collapse supernovae are one of the densest environments in the Universe. Under such conditions, it is conceivable that a first-order phase transition from ordinary nuclear matter to the quark-gluon plasma occurs. This transition releases a large amount of latent heat that can drive a supernova explosion and may imprint a sharp signature in the neutrino signal. We show how this snap feature, if observed at large-scale neutrino detectors, can set competitive limits on the neutrino masses and assist the localization of the supernova via triangulation. The 95\%C.L. limit on the neutrino mass can reach 0.16~eV in Ice-Cube, 0.22~eV in Hyper-Kamiokande, and 0.58~eV in DUNE, for a supernova at a distance of 10 kpc. For the same distance and in the most optimistic neutrino conversion case, the triangulation method can constrain the $1\sigma$ angular uncertainty of the supernova localization within $\sim 0.3^{\circ}-9.0^{\circ}$ in the considered pairs of the detectors, leading to an improvement up to an order of magnitude with respect to the often considered in the literature rise time of the neutronization burst.

Prompted by the recent Dresden-II reactor data we examine its implications for the determination of the weak mixing angle, paying attention to the effect of the quenching function. We also determine the resulting constraints on the unitarity of the neutrino mixing matrix, as well as on the most general type of nonstandard neutral-current neutrino interactions.

The European Spallation Source (ESS), currently under construction in Sweden, will provide an intense pulsed neutrino flux allowing for high-statistics measurements of coherent elastic neutrino-nucleus scattering (CE{\nu}NS) with advanced nuclear recoil detectors. In this paper, we investigate in detail the possibility of constraining non-standard neutrino interactions (NSIs) through such precision CE{\nu}NS measurements at the ESS, considering the different proposed detection technologies, either alone or in combination. We first study the sensitivity to neutral-current NSI parameters that each detector can reach in 3 years of data taking. We then show that operating two detectors simultaneously can significantly improve the expected sensitivity on flavor-diagonal NSI parameters. Combining the results of two detectors turns out to be even more useful when two NSI parameters are assumed to be nonvanishing at a time. In this case, suitably chosen detector combinations can reduce the degeneracies between some pairs of NSI parameters to a small region of the parameter space.

In many theories of quantum gravity quantum fluctuations of spacetime may serve as an environment for decoherence. Here we study quantum-gravitational decoherence of high energy astrophysical neutrinos in the presence of fermionic dark sectors and for a realistic three neutrino scenario. We show how violation of global symmetries expected to arise in quantum gravitational interactions provides a possibility to pin down the number of dark matter fermions in the universe. Furthermore, we predict the expected total neutrino flux and flavor ratios at experiments depending on the flavor composition at the source.

After their generation, cosmological backgrounds of gravitational waves propagate nearly freely but for the expansion of the Universe and the anisotropic stress of free-streaming particles. Primordial signals -- both that from inflation and the infrared spectrum associated to subhorizon production mechanisms -- would carry clean information about the cosmological history of these effects. We study the modulation of the standard damping of gravitational waves by free-streaming radiation due to the decoupling (or recoupling) of interactions. We focus on nonstandard neutrino interactions in effect after the decoupling of weak interactions as well as more general scenarios in the early Universe involving other light relics. We develop semianalytic results in fully free-streaming scenarios to provide intuition for numerical results that incorporate interaction rates with a variety of temerpature dependencies. Finally, we compute the imprint of neutrino interactions on the $B$-mode polarization of the cosmic microwave background, and we comment on other means to infer the presence of such effects at higher frequencies.

We describe the most recent results from the TOTEM collaboration on elastic, inelastic and total cross sections as well as the odderon discovery by the D0 and TOTEM collaborations.

The energy consumption of any of the $\rm e^+e^-$ Higgs factory projects that can credibly operate immediately after the end of LHC, namely three linear colliders (CLIC, operating at $\sqrt{s}=380$GeV; and ILC and $\rm C^3$, operating at $\sqrt{s}=250$ GeV) and two circular colliders (CEPC and FCC-ee, operating at $\sqrt{s}=240$ GeV), will be everything but negligible. Future Higgs boson studies may therefore have a significant environmental impact. This note proposes to include the carbon footprint for a given physics performance as a top-level gauge for the design optimization and, eventually, the choice of the future facility. The projected footprints per Higgs boson produced, evaluated using the 2021 carbon emission of available electricity, are found to vary by a factor 100 depending on the considered Higgs factory project.

We present a full phenomenological and analytical study for the neutrino mass matrix characterized by two vanishing $2\times2$ subtraces. We update one past result in light of the recent experimental data. Out of the fifteen possible textures, we find seven cases can accommodate the experimental data instead of eight ones in the past study. We also introduce few symmetry realizations for viable and nonviable textures based on non-abelian ($A_4$ or $S_4$) flavor symmetry within type II seesaw scenario.

We evaluate the discovery probability of a combined analysis of proposed neutrinoless double-beta decay experiments in a scenario with normal ordered neutrino masses. The discovery probability strongly depends on the value of the lightest neutrino mass, ranging from zero in case of vanishing masses and up to 80-90\% for values just below the current constraints. We study the discovery probability in different scenarios, focusing on the exciting prospect in which cosmological surveys will measure the sum of neutrino masses. Uncertainties in nuclear matrix element calculations partially compensate each other when data from different isotopes are available. Although a discovery is not granted, the theoretical motivations for these searches and the presence of scenarios with high discovery probability strongly motivates the proposed international, multi-isotope experimental program.

We present the approximated analytic expressions for the muon survival probability in a $3+1$ mixing scenario in the presence of matter effect using the S-matrix formalism. We find that all the individual terms contributing to the muon survival probability can significantly reduce to just three contributions. The leading order contribution comes from the three flavor muon survival probability followed by the two sub-leading contributions arising from active-sterile mixing. Furthermore, to more simplify the results we adopt the well known series expansion relations about mass-hierarchy parameter $\alpha = \Delta m^2_{21} / \Delta m^2_{31}$ and the mixing angle $\sin \theta_{13}$ in the vanishing limit of $\alpha^2$. We discuss the relevance of muon survival probability to probe the CP and T-violation studies coming from the new physics. We also compare the analytic relation between vacuum and matter contributions to the muon survival probability at the leading order. Finally, we comment on the probability behavior at the various long baselines relevant to understand the atmospheric-neutrino sector and to resolve the existing mass-hierarchy problem.

We explore the possibility of relating extra dimensions with light and heavy Dirac-type neutral leptons and develop a framework for testing them in various laboratory experiments. The Kaluza-Klein modes in the large extra dimension models of the light neutral leptons could mix with the standard model neutrinos and produce observable effects in the oscillation experiments. We show that the chirality flipping up-scattering processes occurring through either neutrino magnetic dipole moment or the weakly coupled scalar interactions can also produce heavy Kaluza-Klein modes of the corresponding right-handed neutral leptons propagating in one or more extra dimensions. However, to conserve the four-dimensional energy-momentum, their masses must be below the maximum energy of the neutrinos in the initial state. The appreciable size of extra dimensions connected with these heavy neutral leptons can thus affect the cross-sections of these processes. This framework applies to any up-scattering process. Our work here focuses only on its application to the coherent elastic neutrino-nucleus scattering process. We derive constraints on the size of extra dimensions using the COHERENT data in oscillation and up-scattering processes. For model with one large extra dimension for the light neutral leptons, we obtain the limits, $R \sim 3 \ \mu$m (NH) and $R \sim 2.5 \ \mu$m (IH), on the size of extra dimension corresponding to the absolute mass limit, $m_{0} \leq 3 \times 10^{-3}$ eV at 90$\%$ C.L. from the short-baseline oscillations. Using the up-scattering process for heavy neutral leptons, we obtain new parameter spaces between the size of extra dimensions and parameters of the dipole or scalar interactions.

Gamma-ray bursts (GRBs) are the most explosive phenomena and can be used to study the expansion of Universe. In this paper, we compile a long GRB sample for the $E_{\mathrm{iso}}$-$E_{\mathrm{p}}$ correlation from Swift and Fermi observations. The sample contains 221 long GRBs with redshifts from 0.03 to 8.20. From the analysis of data in different redshift intervals, we find no statistically significant evidence for the redshift evolution of this correlation. Then we calibrate the correlation in six sub-samples and use the calibrated one to constrain cosmological parameters. Employing a piece-wise approach, we study the redshift evolution of dark energy equation of state (EOS), and find that the EOS tends to be oscillating at low redshift, but consistent with $-1$ at high redshift. It hints a dynamical dark energy at $2\sigma$ confidence level at low redshift.

The phenomena of neutrino spin flavour precession in the presence of an extraneous magnetic field is a repercussion of neutrino magnetic moment which is consociated with the physics beyond the standard model of electroweak interactions. Ultra high energy neutrinos are spawned from a number of sources in the universe including the highly energetic astrophysical objects such as active galactic nuclei, blazar or supermassive black holes. When such high energy neutrinos pass through any compact stellar objects like neutron stars or white dwarfs, their flux can significantly reduce due to the exorbitant magnetic field provided by these compact objects. For Dirac neutrinos, such phenomena occur due to the conversion of neutrinos to their sterile counterparts. In this work, we consider a neutron star possessing a spatially varying magnetic field which may or may not decay with time. We find that, for the non-decaying magnetic field, the flux of high energy Dirac neutrinos becomes nearly half after passing through the neutron star. The flux is further enfeebled by $\sim 10\%$ in the presence of muons inside the neutron star. For decaying magnetic field, the flux reduction is abated by $\sim 5\%$ as compared to the temporally static magnetic field. In the case of a white dwarf, the depletion of flux is lesser as compared to the neutron stars.

We study the impact of the muon pair production and double pair production processes induced by ultra-high energy photons on the cosmic microwave background. Although the muon pair production cross section is smaller than the electron pair production one, the associated energy loss length is comparable or shorter than the latter (followed by inverse Compton in the deep Klein-Nishina regime) at high-redshift, where the effect of the astrophysical radio background is expected to be negligible. By performing a simulation taking into account the details of $e/\gamma$ interactions at high energies, we show that a significant fraction of the electromagnetic energy injected at $E\gtrsim 10^{19}\,$eV at redshift $z\gtrsim 5$ is channeled into neutrinos. The double pair production plays a crucial role in enhancing the multiplicity of muon production in these electromagnetic cascades. The ultra-high energy neutrino spectrum, yet to be detected, can in principle harbour information on ultra-high energy sources in the young universe, either conventional or exotic ones, with weaker constraints from the diffuse gamma ray flux compared to their low redshift counterparts.

Next generation direct dark matter detection experiments are favorable facilities to probe neutrino properties and light mediators beyond the Standard Model. We explore the implications of the recent data reported by LUX-ZEPLIN (LZ) and XENONnT collaborations on electromagnetic neutrino interactions and neutrino generalized interactions (NGIs). We show that XENONnT places the most stringent upper limits on the effective and transition neutrino magnetic moment (of the order of few $\times 10^{-12}~μ_B$) as well as stringent constraints to neutrino millicharge (of the order of $\sim 10^{-13}~e$)--competitive to LZ--and improved by about one order of magnitude in comparison to existing constraints coming from Borexino and TEXONO. We furthermore explore the XENONnT and LZ sensitivities to simplified models with light NGIs and find improved constraints in comparison to those extracted from Borexino-Phase II data.

The existence of a "knee" at energy ~1 PeV in the cosmic-ray spectrum suggests the presence of Galactic PeV proton accelerators called "PeVatrons". Supernova Remnant (SNR) G106.3+2.7 is a prime candidate for one of these. The recent detection of very high energy (0.1-100 TeV) gamma rays from G106.3+2.7 may be explained either by the decay of neutral pions or inverse Compton scattering by relativistic electrons. We report an analysis of 12 years of Fermi-LAT gamma-ray data which shows that the GeV-TeV gamma-ray spectrum is much harder and requires a different total electron energy than the radio and X-ray spectra, suggesting it has a distinct, hadronic origin. The non-detection of gamma rays below 10 GeV implies additional constraints on the relativistic electron spectrum. A hadronic interpretation of the observed gamma rays is strongly supported. This observation confirms the long-sought connection between Galactic PeVatrons and SNRs. Moreover, it suggests that G106.3+2.7 could be the brightest member of a new population of SNRs whose gamma-ray energy flux peaks at TeV energies. Such a population may contribute to the cosmic-ray knee and be revealed by future very high energy gamma-ray detectors.

The number of events observed in neutrino telescopes depends on the neutrino fluxes in the Earth, their absorption while crossing the Earth and their interaction in the detector. In this paper, we investigate the impact of the QCD dynamics at high energies on the energy dependence of the average inelasticity and angular dependence of the absorption probability during the neutrino propagation through the Earth, as well in the determination of the properties of the incident astrophysical neutrino flux. Moreover, the number of events at the IceCube and IceCube - Gen2 are estimated considering different scenarios for the QCD dynamics and assuming the presence of a hypothetical Super - Glashow flux, which peaks for energies above the Glashow resonance.

The finite size of a neutrino wavepacket at creation can affect its oscillation probability. Here, we consider the electron antineutrino wavepacket and decoherence in the context of the nuclear reactor based experiment JUNO. Given JUNO's high expected statistics [$\sim$100k IBD events ($\bar{\nu}_e p \rightarrow e^+ n$)], long baseline ($\sim$53\,km), and excellent energy resolution [$\sim$$0.03/\sqrt{E_{\mathrm{vis}}~\mathrm{(MeV)}}$], its sensitivity to the size of the wavepacket is expected to be quite strong. Unfortunately, this sensitivity may weaken the experiment's ability to measure the orientation of the neutrino mass hierarchy for currently allowed values of the wavepacket size. Here, we report both the JUNO experiment's ability to determine the hierarchy orientation in the presence of a finite wavepacket and its simultaneous sensitivity to size of the wavepacket and the hierarchy. We find that wavepacket effects are relevant for the hierarchy determination up to nearly two orders of magnitude above the current experimental lower limit on the size, noting that there is no theoretical consensus on the expectation of this value. We also consider the effect in the context of other aspects of JUNO's nominal three-neutrino oscillation measurement physics program and the prospect of future enhancements to sensitivity, including from precise measurements of $\Delta m^2_{3l}$ and a near detector.

Recently announced results from the KATRIN collaboration imply an upper bound on the effective electron anti-neutrino mass $m_{\nu_{e}}$, $m_{\nu_{e}}< 0.8~{\rm eV}/c^{2}$. Here we explore the implications of combining the KATRIN upper bound using a previously inferred lower bound on the smallest neutrino mass state, $m_{i,{\rm min}}\gtrsim 0.4~{\rm eV}/c^{2}$ implied by the stability of white dwarfs and neutron stars in the presence of long-range many-body neutrino-exchange forces. By combining a revised lower bound estimate with the expected final upper bound from KATRIN, we find that the available parameter space for $m_{\nu_{e}}$ may be closed completely within the next few years. We then extend the argument when a single light sterile neutrino flavor is present to set a lower mass limit on sterile neutrinos.

Spatial separation of the wave packets (WPs) of neutrino mass eigenstates leads to decoherence and damping of neutrino oscillations. Damping can also be caused by finite energy resolution of neutrino detectors or, in the case of experiments with radioactive neutrino sources, by finite width of the emitted neutrino line. We study in detail these two types of damping effects using reactor neutrino experiments and experiments with radioactive $^{51}$Cr source as examples. We demonstrate that the effects of decoherence by WP separation can always be incorporated into a modification of the energy resolution function of the detector and so are intimately entangled with it. We estimate for the first time the lengths $\sigma_x$ of WPs of reactor neutrinos and neutrinos from a radioactive $^{51}$Cr source. The obtained values, $\sigma_x = (2\times 10^{-5} - 1.4\times 10^{-4})$ cm, are at least six orders of magnitude larger than the currently available experimental lower bounds. We conclude that effects of decoherence by WP separation cannot be probed in reactor and radioactive source experiments.

Long baseline (LBL) neutrino experiments aim to measure the neutrino oscillation parameters to high precision. These experiments use nuclear targets for neutrino scattering and hence are inflicted with complexities of nuclear effects. Nuclear effects and their percolation into sensitivity measurement of neutrino oscillations parameters are not yet fully understood and therefore need to be dealt with carefully. In a recent work [1], we reported some results on this for NO$\nu$A experiment using the kinematic method of neutrino energy reconstruction, where it was observed that the nuclear effects are important in sensitivity analysis, and inclusion of realistic detector setup specifications increases uncertainty in this analysis as compared to ideal detector case. With this motivation, in this work, we use two methods of neutrino energy reconstruction - kinematic and calorimetric, including the nuclear effects, and study their impact on sensitivity analysis. We consider nuclear interactions such as RPA and 2p2h and compare two energy reconstruction methods with reference to events generation, measurement of neutrino oscillation parameters $\Delta m_{32}^2$ and $\theta_{23}$ for disappearance channel, mass hierarchy sensitivity, and CP-violation sensitivity for appearance channel of the NO$\nu$A experiment. It is observed that with an ideal detector setup, the kinematic method shows significant dependence on nuclear effects compared to the calorimetric method. We also investigate the impact of realistic detector setup for NO$\nu$A in these two methods (with nuclear effects) and find that the calorimetric method shows more bias (uncertainty increases) in sensitivity contours, as compared to the kinematic method. This is found to be true for both the mass hierarchies and for both neutrino and antineutrino incoming beams.

Recent observation of Sagittarius A$^*$ (Sgr A$^*$) by the Event Horizon Telescope (EHT) collaboration has uncovered various unanswered questions in black hole (BH) physics. Besides, it may also probe various beyond the Standard Model (BSM) scenarios. One of the most profound possibilities is the search for ultralight bosons (ULBs) using BH superradiance (SR). EHT observations imply that Sgr A$^*$ has a non-zero spin. Using this observation, we derive bounds on the mass of ULBs with purely gravitational interactions. Considering self-interacting ultralight axions, we constrain new regions in the parameter space of decay constant, for a certain spin of Sgr A$^*$. Future observations of various spinning BHs can improve the present constraints on ULBs.

In the last 70 years, geophysics has established that the Earth's outer core is an FeNi alloy containing a few percent of light elements, whose nature and amount remain controversial today. Besides the classical combinations of silicon and oxygen, hydrogen has been advocated as the only light element that could account alone for both the density and velocity profiles of the outer core. Here we show how this question can be addressed from an independant viewpoint, by exploiting the tomographic information provided by atmospheric neutrinos, weakly-interacting particles produced in the atmosphere and constantly traversing the Earth. We evaluate the potential of the upcoming generation of atmospheric neutrino detectors for such a measurement, showing that they could efficiently detect the presence of 1 wt% of hydrogen in an FeNi core in 50 years of concomitant data taking. We then identify the main requirements for a next-generation detector to perform this measurement in a few years timescale, with the further capability to efficiently discriminate between FeNiH and FeNiSi(x)O(y) models in less than 15 years.

Recent JWST observations suggest an excess of $z\gtrsim10$ galaxy candidates above most theoretical models. Here, we explore how the interplay between halo formation timescales, star formation efficiency and dust attenuation affects the properties and number densities of galaxies we can detect in the early universe. We calculate the theoretical upper limit on the UV luminosity function, assuming star formation is 100% efficient and all gas in halos is converted into stars, and that galaxies are at the peak age for UV emission (~10 Myr). This upper limit is ~4 orders of magnitude greater than current observations, implying these are fully consistent with star formation in $\Lambda$CDM cosmology. In a more realistic model, we use the distribution of halo formation timescales derived from extended Press-Schechter theory as a proxy for star formation rate (SFR). We predict that the galaxies observed so far at $z\gtrsim10$ are dominated by those with the fastest formation timescales, and thus most extreme SFRs and young ages. These galaxies can be upscattered by ~1.5 mag compared to the median UV magnitude vs halo mass relation. This likely introduces a selection effect at high redshift whereby only the youngest ($\lesssim$10 Myr), most highly star forming galaxies (specific SFR$\gtrsim$30 Gyr$^{-1}$) have been detected so far. Furthermore, our modelling suggests that redshift evolution at the bright end of the UV luminosity function is substantially affected by the build-up of dust attenuation. We predict that deeper JWST observations (reaching m~30) will reveal more typical galaxies with relatively older ages (~100 Myr) and less extreme specific SFRs (~10 Gyr$^{-1}$ for a $M_\mathrm{UV}$ ~ -20 galaxy at z~10).

We consider the consequences of a matter power spectrum which rises on small scales until eventually being cutoff by microphysical processes associated with the particle nature of dark matter. Evolving the perturbations of a weakly interacting massive particle from before decoupling until deep in the nonlinear regime, we show that nonlinear structure can form abundantly at very high redshifts. In such a scenario, dark matter annihilation is substantially increased after matter-radiation equality. Furthermore, since the power spectrum can be increased over a broad range of scales, the first star forming halos may form earlier than usual as well. The next challenge is determining how early Universe observations may constrain such enhanced dark matter perturbations.

Measuring observables to constrain models using maximum-likelihood estimation is fundamental to many physics experiments. The Profiled Feldman-Cousins method described here is a potential solution to common challenges faced in constructing accurate confidence intervals: small datasets, bounded parameters, and the need to properly handle nuisance parameters. This method achieves more accurate frequentist coverage than other methods in use, and is generally applicable to the problem of parameter estimation in neutrino oscillations and similar measurements. We describe an implementation of this method in the context of the NOvA experiment.

Galaxy mergers at high redshifts trigger the activity of their central supermassive black holes, eventually also leading to their coalescence -- and a potential source of low-frequency gravitational waves detectable by the SKA Pulsar Timing Array (PTA). Two key parameters related to the fuelling of black holes are the Eddington ratio of quasar accretion $\eta_{\rm Edd}$, and the radiative efficiency of the accretion process, $\epsilon$ (which affects the so-called active lifetime of the quasar, $t_{\rm QSO}$). We forecast the regime of detectability of gravitational wave events with SKA PTA, finding the associated binaries to have orbital periods on the order of weeks to years, observable through relativistic Doppler velocity boosting and/or optical variability of their light curves. Combining the SKA regime of detectability with the latest observational constraints on high-redshift black hole mass and luminosity functions, and theoretically motivated prescriptions for the merger rates of dark matter haloes, we forecast the number of active counterparts of SKA PTA events expected as a function of primary black hole mass at $z \gtrsim 6$. We find that the quasar counterpart of the most massive black holes will be ${uniquely \ localizable}$ within the SKA PTA error ellipse at $z \gtrsim 6$. We also forecast the number of expected counterparts as a function of the quasars' Eddington ratio and active lifetime. Our results show that SKA PTA detections can place robust constraints on the seeding and growth mechanisms of the first supermassive black holes.

Jupiter, the fascinating largest planet in the solar system, has been visited by nine spacecraft, which have collected a significant amount of data about Jovian properties. In this paper, we show that one type of the in situ measurements on the relativistic electron fluxes could be used to probe dark matter (DM) and dark mediator between the dark sector and our visible world. Jupiter, with its immense weight and cool core, could be an ideal capturer for DM with masses around the GeV scale. The captured DM particles could annihilate into long-lived dark mediators such as dark photons, which subsequently decay into electrons and positrons outside Jupiter. The charged particles, trapped by the Jovian magnetic field, have been measured in Jupiter missions such as the Galileo probe and the Juno orbiter. We use the data available to set upper bounds on the cross section of DM scattering off nucleons, $\sigma_{\chi n}$, for dark mediators with lifetime of order ${\cal O}(0.1-1)$s. The results show that data from Jupiter missions already probe regions in the parameter space un- or under-explored by existing DM searches, e.g., constrain $\sigma_{\chi n}$ of order $(10^{-40} - 10^{-38})$ cm$^2$ for 1 GeV DM dominantly annihilating into $e^+e^-$ through dark mediators. This study serves as an example and an initial step to explore the full physics potential of the large planetary datasets from Jupiter missions. We also outline several other potential directions related to secondary products of electrons, positron signals and solar axions.

We present the first comprehensive discussion of constraints on the cosmic neutrino background (C$\nu$B) overdensity, including theoretical, experimental and cosmological limits for a wide range of neutrino masses and temperatures. Additionally, we calculate the sensitivities of future direct and indirect relic neutrino detection experiments and compare the results with the existing constraints, extending several previous analyses by taking into account that the C$\nu$B reference frame may not be aligned with that of the Earth. The Pauli exclusion principle strongly disfavours overdensities $\eta_\nu \gg 1$ at small neutrino masses, but allows for overdensities $\eta_{\nu}\lesssim 125$ at the KATRIN mass bound $m_{\nu} \simeq 0.8\,\mathrm{eV}$. On the other hand, cosmology strongly favours $0.2 \lesssim \eta_{\nu} \lesssim 3.5$ in all scenarios. We find that direct detection proposals are capable of observing the C$\nu$B without a significant overdensity for neutrino masses $m_{\nu} \gtrsim 50\,\mathrm{meV}$, but require an overdensity $\eta_{\nu} \gtrsim 3\times 10^5$ outside of this range. We also demonstrate that relic neutrino detection proposals are sensitive to the helicity composition of the C$\nu$B, whilst some may be able to distinguish between Dirac and Majorana neutrinos.

OJ 287 is a blazar thought to be a binary system containing a ~ 18 billion solar mass primary black hole accompanied by a ~ 150 million solar mass secondary black hole in an eccentric orbit, which triggers electromagnetic flares twice in every ~ 12 year orbital period when it traverses the accretion disk of the primary. The times of these emissions are consistent with the predictions of general relativity calculated to the 4.5th post-Newtonian order. The orbit of the secondary black hole samples the gravitational field at distances between O(10) and O(50) Schwarzschild radii around the primary, and hence is sensitive to the possible presence of a dark matter spike around it. We find that the agreement of general-relativistic calculations with the measured timings of flares from OJ 287 constrains the mass of such a spike to < 3% of the primary mass.

We check if the first significant digit of the dispersion measure of pulsars and Fast Radio Bursts (using the CHIME catalog) is consistent with the Benford distribution. We find a large disagreement with Benford's law with $\chi^2$ close to 80 for 8 degrees of freedom for both these aforementioned datasets. This corresponds to a discrepancy of about 7$\sigma$. Therefore, we conclude that the dispersion measures of pulsars and FRBs do not obey Benford's law.

Neutrinos are the second most ubiquitous Standard Model particles in the universe. On the other hand, they are also the ones least likely to interact. Connecting these two points suggests that when a neutrino is detected, it can divulge unique pieces of information about its source. Among the known neutrino sources, core-collapse supernovae in the universe are the most abundant for MeV-energies. On average, a single collapse happens every second in the observable universe and produces $10^{58}$ neutrinos. The flux of neutrinos reaching the Earth from all the core-collapse supernovae in the universe is known as diffuse supernova neutrino background. In this Chapter, the basic prediction for the diffuse supernova neutrino background is presented. This includes a discussion of an average neutrino signal from a core-collapse supernova, variability of that signal due to the remnant formed in the process, and uncertainties connected to the other astrophysical parameters determining the diffuse flux, such as cosmological supernova rate. In addition, the current experimental limits and detection perspectives of diffuse supernova neutrino background are reported.

Certain inflationary models like Natural inflation (NI) and Coleman-Weinberg inflation (CWI) are disfavoured by cosmological data in the standard $\Lambda\textrm{CDM}+r$ model (where $r$ is the scalar-to-tensor ratio), as these inflationary models predict the regions in the $n_s-r$ parameter space that are excluded by the cosmological data at more than 2$\sigma$ (here $n_s$ is the scalar spectral index). The same is true for single field inflationary models with an inflection point that can account for all or majority of dark matter in the form of PBHs (primordial black holes). Cosmological models incorporating strongly self-interacting neutrinos (with a heavy mediator) are, however, known to prefer lower $n_s$ values compared to the $\Lambda\rm CDM$ model. Considering such neutrino self-interactions can, thus, open up the parameter space to accommodate the above inflationary models. In this work, we implement the massive neutrino self-interactions with a heavy mediator in two different ways: flavour-universal (among all three neutrinos), and flavour-specific (involving only one neutrino species). We implement the new interaction in both scalar and tensor perturbation equations of neutrinos. Interestingly, we find that the current cosmological data can support the aforementioned inflationary models at 2$\sigma$ in the presence of such neutrino self-interactions.

We present robust, model-marginalized limits on both the total neutrino mass ($\sum m_\nu$) and abundance ($N_{\rm eff}$) to minimize the role of parameterizations, priors and models when extracting neutrino properties from cosmology. The cosmological observations we consider are CMB temperature fluctuation and polarization measurements, Supernovae Ia luminosity distances, BAO observations and determinations of the growth rate parameter from the Data Release 16 of the Sloan Digital Sky Survey IV. The degenerate neutrino mass spectrum (which implies $\sum m_\nu>0$) is weakly (moderately) preferred over the normal and inverted hierarchy possibilities, which imply the priors $\sum m_\nu>0.06$ and $\sum m_\nu>0.1$ eV respectively. Concerning the underlying cosmological model, the $\Lambda$CDM minimal scenario is almost always strongly preferred over the possible extensions explored here. The most constraining $95\%$ CL bound on the total neutrino mass in the $\Lambda$CDM+$\sum m_\nu$ picture is $\sum m_\nu< 0.087$ eV. The parameter $N_{\rm eff}$ is restricted to $3.08\pm 0.17$ ($68\%$ CL) in the $\Lambda$CDM+$N_{\rm eff}$ model. These limits barely change when considering the $\Lambda$CDM+$\sum m_\nu$+$N_{\rm eff}$ scenario. Given the robustness and the strong constraining power of the cosmological measurements employed here, the model-marginalized posteriors obtained considering a large spectra of non-minimal cosmologies are very close to the previous bounds, obtained within the $\Lambda$CDM framework in the degenerate neutrino mass spectrum. Future cosmological measurements may improve the current Bayesian evidence favouring the degenerate neutrino mass spectra, challenging therefore the consistency between cosmological neutrino mass bounds and oscillation neutrino measurements, and potentially suggesting a more complicated cosmological model and/or neutrino sector.

Dynamical Chern-Simons gravity (dCS) is a four-dimensional parity-violating extension of general relativity. Current models predict the effect of this extension to be negligible due to large decay constants $f$ close to the scale of grand unified theories. Here, we present a construction of dCS allowing for much smaller decay constants, ranging from sub-eV to Planck scales. Specifically, we show that if there exists a fermion species with strong self-interactions, the short-wavelength fermion modes form a bound state. This bound state can then undergo dynamical symmetry breaking and the resulting pseudoscalar develops Yukawa interactions with the remaining long-wavelength fermion modes. Due to this new interaction, loop corrections with gravitons then realize a linear coupling between the pseudoscalar and the gravitational Chern-Simons term. The strength of this coupling is set by the Yukawa coupling constant divided by the fermion mass. Therefore, since self-interacting fermions with small masses are ideal, we identify neutrinos as promising candidates. For example, if a neutrino has a mass $m_\nu \lesssim {\rm meV}$ and the Yukawa coupling is order unity, the dCS decay constant can be as small as $f \sim 10^3 m_\nu \lesssim {\rm eV}$. We discuss other potential choices for fermions.

The majority of astrophysical neutrinos have undetermined origins. The IceCube Neutrino Observatory has observed astrophysical neutrinos but has not yet identified their sources. Blazars are promising source candidates, but previous searches for neutrino emission from populations of blazars detected in $\gtrsim$ GeV gamma-rays have not observed any significant neutrino excess. Recent findings in multi-messenger astronomy indicate that high-energy photons, co-produced with high-energy neutrinos, are likely to be absorbed and reemitted at lower energies. Thus, lower-energy photons may be better indicators of TeV-PeV neutrino production. This paper presents the first time-integrated stacking search for astrophysical neutrino emission from MeV-detected blazars in the first Fermi-LAT low energy catalog (1FLE) using ten years of IceCube muon-neutrino data. The results of this analysis are found to be consistent with a background-only hypothesis. Assuming an E$^{-2}$ neutrino spectrum and proportionality between the blazars' MeV gamma-ray fluxes and TeV-PeV neutrino flux, the upper limit on the 1FLE blazar energy-scaled neutrino flux is determined to be $1.64 \times 10^{-12}$ TeV cm$^{-2}$ s$^{-1}$ at 90% confidence level. This upper limit is approximately 1% of IceCube's diffuse muon-neutrino flux measurement.

A search for interactions from solar $^8$B neutrinos elastically scattering off xenon nuclei using PandaX-4T commissioning data is reported. The energy threshold of this search is further lowered compared with the previous search for dark matter, with various techniques utilized to suppress the background that emerges from data with the lowered threshold. A blind analysis is performed on the data with an effective exposure of 0.48 tonne$\cdot$year, and no significant excess of events is observed. Among results obtained using the neutrino-nucleus coherent scattering, our results give the best constraint on the solar $^8$B neutrino flux. We further provide a more stringent limit on the cross section between dark matter and nucleon in the mass range from 3 to 9 GeV/c$^2$.

One of the major open problems of neutrino physics is MO (mass ordering). We discuss the prospects of measuring MO with two under-construction experiments T2HK and JUNO. JUNO alone is expected to measure MO with greater than $3\sigma$ significance as long as certain experimental challenges are met. In particular, JUNO needs better than 3$\%$ energy resolution for MO measurement. On the other hand, T2HK has rather poor prospects at measuring the MO, especially for certain ranges of the CP violating parameter $\delta_{\rm CP}$, posing a major drawback for T2HK. In this letter we show that the synergy between JUNO and T2HK will bring two-fold advantage. Firstly, the synergy between the two experiments helps us determine the MO at a very high significance. With the baseline set-up of the two experiments, we have a greater than $9\sigma$ determination of the MO for all values of $\delta_{\rm CP}$. Secondly, the synergy also allows us to relax the constraints on the two experiments. We show that JUNO, could perform extremely well even for energy resolution of 5$\%$, while for T2HK the MO problem with "bad" values of $\delta_{\rm CP}$ goes away. The MO sensitivity for the combined analysis is expected to be greater than $6\sigma$ for all values of $\delta_{\rm CP}$ and with just 5$\%$ energy resolution for JUNO.

The interaction of neutrino transition magnetic dipole moments with magnetic fields can give rise to the phenomenon of neutrino spin-flavour precession (SFP). For Majorana neutrinos, the combined action of SFP of solar neutrinos and flavour oscillations would manifest itself as a small, yet potentially detectable, flux of electron antineutrinos coming from the Sun. Non-observation of such a flux constrains the product of the neutrino magnetic moment $\mu$ and the strength of the solar magnetic field $B$. We derive a simple analytical expression for the expected $\bar{\nu}_e$ appearance probability in the three-flavour framework and we use it to revisit the existing experimental bounds on $\mu B$. A full numerical calculation has also been performed to check the validity of the analytical result. We also present our numerical results in energy-binned form, convenient for analyses of the data of the current and future experiments searching for the solar $\bar{\nu}_e$ flux. In addition, we give a comprehensive compilation of other existing limits on neutrino magnetic moments and of the expressions for the probed effective magnetic moments in terms of the fundamental neutrino magnetic moments and leptonic mixing parameters.

We show how a minimization principle of quantum entanglement between the oscillating flavors of a neutrino leads to a unique prediction for the CP-violation phase in the neutrino sector without assuming extra symmetries in the Standard Model. We find a theoretical prediction consistent with either no CP-violation or a very small presence of it.

We discuss the transition and survival probabilities in $3+1$ neutrino flavor mixing scenario in presence of matter effects. We adopt the well-known OMSD(One Mass Scale Dominance) approximation to carry out our analysis. After that we perform series expansion about $\sin \theta_{13}$ term upto second order. We find that our results are consistent with the already existing $\alpha - \sin \theta_{13}$ approximated relations in the limit of vanishing $\alpha$ and phases involving sterile neutrinos. We also figure out that survival transition probability becomes independent of the fundamental and sterile CP phases under our formalism. Hence, it provides us a new way to look at only matter effects contribution to oscillation probability. Also, the transition probability at the same time gives an independent study of CP-violation arising from the sterile phases, in the vicinity of fundamental CP violation phase. We provide the relation for the atmospheric probability in the presence of matter by performing the series expansion upto linear order about parameter $A (= 2EV)$, with V being the effective matter potential under OMSD approximation.

In this work we study the impact of new physics, stimulated by flavor anomalies, on neutrino oscillations through dense dark matter halo. Inspired by a model where a Majorana dark matter fermion and two new scalar fields contribute to $b \to s \mu^+ \mu^-$ transition at the one loop level, we study the impact of neutrino-dark matter interaction on the oscillation patterns of ultra-high energy cosmic neutrinos passing through this muonphilic halo located near the center of Milky Way. We find that due to this interaction, the flavor ratios of neutrinos reaching earth would be different from that of vacuum oscillations. We also consider a $Z'$ model driven by $L_{\mu}-L_{\tau}$ symmetry and containing a vector-like fermion as a dark matter candidate. It was previously shown that for such a model, the three flavors of neutrinos decouple from each other. This will render a flavor ratio similar to that of vacuum oscillations. Therefore, the interaction of neutrinos with dense dark matter halo can serve as an important tool to discriminate between flavor models with a dark connection.

We propose a new probe of cosmic relic neutrinos (C$\nu$B) using their resonant scattering against cosmogenic neutrinos. Depending on the lightest neutrino mass and the energy spectrum of the cosmogenic neutrino flux, a Standard Model vector meson (such as a hadronic $\rho$) resonance can be produced via $\nu\bar{\nu}$ annihilation. This leads to a distinct absorption feature in the cosmogenic neutrino flux at an energy solely determined by the meson mass and the neutrino mass, apart from redshift. By numerical coincidence, the position of the $\rho$-resonance overlaps with the originally predicted peak of the Greisen-Zatsepin-Kuzmin (GZK) neutrino flux, which offers an enhanced absorption effect at higher redshifts. We show that this absorption feature in the GZK neutrino flux may be observable in future radio-based neutrino observatories, such as IceCube-Gen2 radio, provided there exists a large overdensity in the C$\nu$B distribution. This therefore provides a new probe of C$\nu$B clustering at large redshifts, complementary to the laboratory probes (such as KATRIN) at zero redshift.

The existence of Large Extra Dimensions can be probed in various neutrino experiments. We analyze several neutrino data sets in a model with a dominant large extra dimension. We show that the Gallium anomaly can be explained with neutrino oscillations induced by the large extra dimension, but the region of parameter space which is preferred by the Gallium anomaly is in tension with the bounds from reactor rate data, as well as the data of Daya Bay and MINOS. We also present bounds obtained from the analysis of the KATRIN data. We show, that current experiments can put strong bounds on the size $R_{\text{ED}}$ of the extra dimension: $R_{\text{ED}} < 0.20~\mu\text{m}$ and $R_{\text{ED}} < 0.10~\mu\text{m}$ at 90\% C.L. for normal and inverted ordering of the standard neutrino masses, respectively.

We analyze the sensitivity of the Deep Underground Neutrino Experiment (DUNE) to a sterile neutrino, combining information from both near and far detectors. We quantify often-neglected effects which may impact the event rate estimation in a 3+1 oscillation scenario. In particular, we find that taking into account the information on the neutrino production point, in contrast to assuming a pointlike neutrino source, affects DUNE's sterile exclusion reach. Visible differences remain after the inclusion of energy bin-to-bin uncorrelated systematics. Instead, implementing exact oscillation formulae for near detector events, including a two slab density profile, does not result in any visible change in the sensitivity.

In light of the exciting campaign of cosmogenic neutrino detection, we investigate the double and multiple tau bangs detectable at future tau neutrino telescopes. Such events are expected from the Standard Model (SM) higher-order processes, which can be easily identified with broad techniques anticipated at future tau neutrino telescopes. We find that SM perturbative processes can already contribute observable double-bang events to telescopes with a sensitivity of collecting $\mathcal{O}(100)$ cosmogenic neutrino events. The detectable but suppressed rate in fact makes the double and multiple bangs an excellent probe of SM unknowns and possible new physics beyond. As a case study, the nonperturbative sphaleron process, which can copiously produce multiple tau bangs, is explored.

We revisit cosmological constraints on the sum of the neutrino masses $\Sigma m_\nu$ from a combination of full-shape BOSS galaxy clustering [$P(k)$] data and measurements of the cross-correlation between Planck Cosmic Microwave Background (CMB) lensing convergence and BOSS galaxy overdensity maps [$C^{\kappa \text{g}}_{\ell}$], using a simple but theoretically motivated model for the scale-dependent galaxy bias in auto- and cross-correlation measurements. We improve upon earlier related work in several respects, particularly through a more accurate treatment of the correlation and covariance between $P(k)$ and $C^{\kappa \text{g}}_{\ell}$ measurements. When combining these measurements with Planck CMB data, we find a 95% confidence level upper limit of $\Sigma m_\nu<0.14\,{\rm eV}$, while slightly weaker limits are obtained when including small-scale ACTPol CMB data, in agreement with our expectations. We confirm earlier findings that (once combined with CMB data) the full-shape information content is comparable to the geometrical information content in the reconstructed BAO peaks given the precision of current galaxy clustering data, discuss the physical significance of our inferred bias and shot noise parameters, and perform a number of robustness tests on our underlying model. While the inclusion of $C^{\kappa \text{g}}_{\ell}$ measurements does not currently appear to lead to substantial improvements in the resulting $\Sigma m_{\nu}$ constraints, we expect the converse to be true for near-future galaxy clustering measurements, whose shape information content will eventually supersede the geometrical one.

Black-hole superradiance has been used to place very strong bounds on a variety of models of ultralight bosons such as axions, new light scalars, and dark photons. It is common lore to believe that superradiance bounds are broadly model independent and therefore pretty robust. In this work we show however that superradiance bounds on dark photons can be challenged by simple, compelling extensions of the minimal model. In particular, if the dark photon populates a larger dark sector and couples to dark fermions playing the role of dark matter, then superradiance bounds can easily be circumvented, depending on the mass and (dark) charge of the dark matter.

T2HK is an upcoming long-baseline experiment in Japan which will have two water Cherenkov detector tanks of 187 kt volume each at distance of 295 km from the source. An alternative project, T2HKK is also under consideration where one of the water tanks will be moved to Korea at a distance of 1100 km. The flux at 295 km will cover the first oscillation maximum and the flux at 1100 km will mainly cover the second oscillation maximum. As physics sensitivity at the dual baseline rely on variation in statistics, dependence of systematic uncertainty, effect of second oscillation maximum and matter density, 187 kt detector volume at 295 km and 187 kt detector volume at 1100 km may not be the optimal configuration of T2HKK. Therefore, we have tried to optimize the ratio of the detector volume at both the locations by studying the interplay between the above mentioned parameters. For the analysis of neutrino mass hierarchy, octant of $\theta_{23}$ and CP precision, we have considered two values of $\delta_{\rm{CP}}$ as 270$^\circ$ and $0^\circ$ and for CP violation we have considered the value of $\delta_{\rm CP}= 270^\circ$. These values are motivated by the current best-fit values of this parameter as obtained from the experiments T2K and NO$\nu$A. Interestingly we find that if the systematic uncertainty is negligible then the T2HK setup i.e., when both the detector tanks are placed at 295 km gives the best results in terms of hierarchy sensitivity at $\delta_{\rm CP}= 270^\circ$, octant sensitivity, CP violation sensitivity and CP precision sensitivity at $\delta_{\rm CP}= 0^\circ$. For current values of systematic errors, we find that neither T2HK, nor T2HKK setup is giving better results for hierarchy, CP violation and CP precision sensitivity. The optimal detector volume which is of the range between 255 kt to 345 kt at 1100 km gives better results in those above mentioned parameters.

Non-standard neutrino interactions with a massive boson can produce the bosons in the core of core-collapse supernovae (SNe). After the emission of the bosons from the SN core, their subsequent decays into neutrinos can modify the SN neutrino flux. We show future observations of neutrinos from a next galactic SN in Super-Kamiokande (SK) and Hyper-Kamiokande (HK) can probe flavor-universal non-standard neutrino couplings to a light boson, improving the previous limit from the SN 1987A neutrino burst by several orders of magnitude. We also discuss sensitivity of the flavor-universal non-standard neutrino interactions in future observations of diffuse neutrinos from all the past SNe, known as the diffuse supernova neutrino background (DSNB). According to our analysis, observations of the DSNB in HK, JUNO and DUNE experiments can probe such couplings by a factor of $\sim 2$ beyond the SN 1987A constraint. However, our result is also subject to a large uncertainty concerning the precise estimation of the DSNB.

Recently we have developed a method called ``Symmetry Finder'' (SF) for hunting the reparametrization symmetry in the three-neutrino system in matter. Here, we apply SF to the Denton {\it et al.} (DMP) perturbation theory extended by including unitarity violation (UV), a possible low-energy manifestation of physics beyond the $\nu$SM. Implementation of UV into the SF framework yields the additional two very different constraints, which nonetheless allow remarkably consistent solutions, the eight DMP-UV symmetries. Treatment of one of the constraints, the genuine non-unitary part, leads to the key identity which entails the UV $\alpha$ parameter transformation only by rephasing, which innovates the invariance proof of the Hamiltonian. The quantum mechanical nature of the symmetry dictates the both $\nu$SM and UV variables to transform jointly, through which the response of the two sectors are related to reveal their interplay. Thus, the symmetry can serve for a tool for diagnostics, probing the interrelation between the $\nu$SM and a low-energy description of new physics. Problem of SF symmetry in vacuum is revisited to complete eight symmetries akin to DMP's.

Cosmic strings that couple to neutrinos may account for a portion of the high-energy astrophysical neutrino (HEAN) flux seen by IceCube. Here, we calculate the observed spectrum of neutrinos emitted from a population of cosmic string loops that contain quasi-cusps, -kinks, or kink-kink collisions. We consider two broad neutrino emission models: one where these string features emit a neutrino directly, and one where they emit a scalar particle which then eventually decays to a neutrino. In either case, the spectrum of cosmic string neutrinos does not match that of the observed HEAN spectrum. We thus find that the maximum contribution of cosmic string neutrinos, through these two scenarios, to be at most $\sim 45$ % of the observed flux. However, we also find that the presence of cosmic string neutrinos can lead to bumps in the observed neutrino spectrum. Finally, for each of the models presented, we present the viable parameter space for neutrino emission.

In the absence of high-statistics supernova neutrino measurements, estimates of the diffuse supernova neutrino background (DSNB) hinge on the precision of simulations of core-collapse supernovae. Understanding the cooling phase of protoneutron star (PNS) evolution ($\gtrsim1\,{\rm s}$ after core bounce) is crucial, since approximately 50% of the energy liberated by neutrinos is emitted during the cooling phase. We model the cooling phase with a hybrid method by combining the neutrino emission predicted by 3D hydrodynamic simulations with several cooling-phase estimates, including a novel two-parameter correlation depending on the final baryonic PNS mass and the time of shock revival. We find that the predicted DSNB event rate at Super-Kamiokande can vary by a factor of $\sim2-3$ depending on the cooling-phase treatment. We also find that except for one cooling estimate, the range in predicted DSNB events is largely driven by the uncertainty in the neutrino mean energy. With a good understanding of the late-time neutrino emission, more precise DSNB estimates can be made for the next generation of DSNB searches.

The pair annihilation of neutrinos $(\nu\overline{\nu}\rightarrow e^+e^-)$ can energize violent stellar explosions such as gamma ray bursts (GRBs). The energy in this neutrino heating mechanism can be further enhanced by modifying the background spacetime over that of Newtonian spacetime. However, one cannot attain the maximum GRB energy $(\sim 10^{52}~\rm{erg})$ in either the Newtonian background or Schwarzschild and Hartle-Thorne background. On the other hand, using modified gravity theories or the Quintessence field as background geometries, the maximum GRB energy can be reached. In this paper, we consider extending the standard model by an extra $U(1)_{\rm{B-L}}$ gauge group and augmenting the energy deposition by neutrino pair annihilation process including contributions mediated by the $Z^\prime$ gauge boson belonging to this model. From the observed energy of GRB, we obtain constraints on $U(1)_{\rm{B-L}}$ gauge coupling in different background spacetimes. We find that the bounds on gauge coupling in modified gravity theories and quintessence background are stronger than those coming from the neutrino-electron scattering experiments in the limit of small gauge boson masses. Future GRB observations with better accuracy can further strengthen these bounds.

Photodisintegration is a main energy loss process for ultrahigh-energy cosmic-ray (UHECR) nuclei in intergalactic space. Therefore, it is crucial to understand systematic uncertainty in photodisintegration when simulating the propagation of UHECR nuclei. In this work, we calculated the cross sections using the random phase approximation (RPA) of density functional theory (DFT), a microscopic nuclear model. We calculated the $E1$ strength of 29 nuclei using three different density functionals. We obtained the cross sections of photonuclear reactions, including photodisintegration, with the $E1$ strength. Then, we implemented the cross sections in the cosmic-ray propagation code CRPropa. We found that assuming certain astrophysical parameter values, the difference between UHECR energy spectrum predictions using the RPA calculation and the default photodisintegration model in CRPropa can be more than the statistical uncertainty of the spectrum. We also found that the differences between the RPA calculations and CRPropa default in certain astrophysical parameters obtained by a combined fit of UHECR energy spectrum and composition data assuming a phenomenological model of UHECR sources can be more than the uncertainty of the data.

We show the prospects of probing neutral-current non-standard interaction (NSI) in the propagation of atmospheric neutrinos in future large-volume neutrino experiments including DUNE, HK, KNO, and ORCA. For DUNE, we utilize its ability of identifying the tau neutrino event and combine the $\nu_\tau$ appearance with the $\nu_\mu$ disappearance. Based on our simulated results, the ten years of data taking of the atmospheric neutrinos can enormously improve the bounds on the NSI parameters $\varepsilon_{\mu \tau}, | \varepsilon_{\mu \mu} - \varepsilon_{\tau \tau} |$, $\varepsilon_{e \mu }$, $\varepsilon_{e \tau}$ and $| \varepsilon_{\mu \mu} - \varepsilon_{e e} |$ by a couple of orders of magnitudes. In addition, we show the expected correlations between the CP-violation phase $\delta_{CP}$ and the NSI parameters $\varepsilon_{e\mu}, \varepsilon_{e\tau}$, and $|\varepsilon_{ee} - \varepsilon_{\mu \mu}|$ and confirm the potentials of DUNE, HK, KNO (combined with HK) in excluding the "No CP violation" hypothesis at 1$\sigma$, 2$\sigma$, and 3$\sigma$, respectively.

The concept of putting a neutrino detector in close orbit of the sun has been unexplored until very recently. The primary scientific return is to vastly enhance our understanding of the solar interior, which is a major NASA goal. Preliminary calculations show that such a spacecraft, if properly shielded, can operate in space environments while taking data from neutrino interactions. These interactions can be distinguished from random background rates of solar electromagnetic emissions, galactic charged cosmic-rays, and gamma-rays by using a double pulsed signature. Early simulations of this project have shown this veto schema to be successful in eliminating background and identifying the neutrino interaction signal in upwards of 75% of gamma ray interactions and nearly 100% of other interactions. Hence, we propose a new instrument to explore and study our sun. Due to inverse square scaling, this instrument has the potential to outperform earth-based experiments in several domains such as making measurements not accessible from the earth's orbit.

The decay of the primordial isotopes $^{238}\mathrm{U}$, $^{235}\mathrm{U}$, $^{232}\mathrm{Th}$, and $^{40}\mathrm{K}$ have contributed to the terrestrial heat budget throughout the Earth's history. Hence the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth model. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18-year observation time, and improvements in detector background levels mainly by an 8-year almost rector-free period now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. Herein the KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High-Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2$\sigma$ assuming a homogeneous heat producing element distribution in the mantle.

The Hyper-Kamiokande (HyperK) experiment is expected to precisely measure the Diffuse Supernova Neutrino Background (DSNB). This requires that the backgrounds in the relevant energy range are well understood. One possible background that has not been considered thus far is the annihilation of low-mass dark matter (DM) to neutrinos. We conduct simulations of the DSNB signal and backgrounds in HyperK, and quantify the extent to which DM annihilation products can pollute the DSNB signal. We find that the presence of DM could affect the determination of the correct values of parameters of interest for DSNB physics, such as effective neutrino temperatures and star formation rates. While this opens the possibility of simultaneously characterising the DNSB and discovering dark matter via indirect detection, we argue that it would be hard to disentangle the two contributions due to the lack of angular information available at low energies.

We estimated the radiative efficiency and spin value for a number of local active galactic nuclei with z < 0.34 using 3 popular models connecting the radiative efficiency with such parameters of AGNs as mass of supermassive black hole, angle between the line of sight and the axis of the accretion disk and bolometric luminosity. Analysis of the obtained data shown that the spin value decreases with cosmic time, which is in agreement with results of theoretical calculations for low redshift AGNs of other authors. Also we found that the spin value increases with the increasing mass of SMBH and bolometric luminosity. This is the expected result that corresponds to theoretical calculations. Analysis of the distribution of the spin values shown a pronounced peak in the distribution in 0.75 < a < 1.0 range. ~ 40% of objects have spin a > 0.75 and ~ 50% of objects have spin a > 0.5. This results are in a good agreement with our previous results and with the results of other authors.

We study the impact of a binary companion on black hole superradiance at orbital frequencies away from the gravitational-collider-physics (GCP) resonance bands. A superradiant state can couple to a strongly absorptive state via the tidal perturbation of the companion, thereby acquiring a suppressed superradiance rate. Below a critical binary separation, this superradiance rate becomes negative, and the boson cloud gets absorbed by the black hole. This critical binary separation leads to tight constraints on GCP. Especially, a companion with mass ratio $q>10^{-3}$ invalidates all GCP fine structure transitions, as well as almost all Bohr transitions except those from the $|\psi_{211}\rangle$ state. Meanwhile, the backreaction on the companion manifests itself as a torque acting on the binary, producing floating/sinking orbits that can be verified via pulsar timing. In addition, the possible termination of cloud growth may help to alleviate the current bounds on the ultralight boson mass from various null detections.

If ultra-light dark matter (ULDM) exists and couples to neutrinos, the neutrino oscillation probability might be significantly altered by a parametric resonance. This resonance can occur if the typical frequency of neutrino flavor-oscillations $\Delta m^2/(2E)$, where $\Delta m^2$ is the mass-squared difference of the neutrinos and $E$ is the neutrino energy, matches the oscillation frequency of the ULDM field, determined by its mass, $m_\phi$. The resonance could lead to observable effects even if the ULDM coupling is very small, and even if its typical oscillation period, given by $\tau_\phi=2\pi/m_\phi$, is much shorter than the experimental temporal resolution. Defining a small parameter $\epsilon_\phi$ to be the ratio between the contribution of the ULDM field to the neutrino mass and the vacuum value of the neutrino mass, the impact of the resonance is particularly significant if $\epsilon_\phi m_\phi L\gtrsim 4$, where $L$ is the distance between the neutrino source and the detector. Such parametric resonance can improve the fit to the KamLAND experiment measurements by about $3.5\,\sigma$ compared to standard oscillations. This scenario will be tested by the JUNO experiment.

The ultrahigh energy range of neutrino physics (above $\sim 10^{7} \, \mathrm{GeV}$), as yet devoid of detections, is an open landscape with challenges to be met and discoveries to be made. Neutrino-nucleon cross sections in that range - with center-of-momentum energies $\sqrt{s} \gtrsim 4 \, \mathrm{TeV}$ - are powerful probes of unexplored phenomena. We present a simple and accurate model-independent framework to evaluate how well these cross sections can be measured for an unknown flux and generic detectors. We also demonstrate how to characterize and compare detector sensitivity. We show that cross sections can be measured to $\simeq ^{+65}_{-30}$% precision over $\sqrt{s} \simeq$ 4-140 TeV ($E_\nu = 10^7$-$10^{10}$ GeV) with modest energy and angular resolution and $\simeq 10$ events per energy decade. Many allowed novel-physics models (extra dimensions, leptoquarks, etc.) produce much larger effects. In the distant future, with $\simeq 100$ events at the highest energies, the precision would be $\simeq 15\%$, probing even QCD saturation effects.

We explore the assumption, widely used in many astrophysical calculations, that the stellar initial mass function (IMF) is universal across all galaxies. By considering both a canonical Salpeter-like IMF and a non-universal IMF, we are able to compare the effect of different IMFs on multiple observables and derived quantities in astrophysics. Specifically, we consider a non-universal IMF which varies as a function of the local star formation rate, and explore the effects on the star formation rate density (SFRD), the extragalactic background light, the supernova (both core-collapse and thermonuclear) rates, and the diffuse supernova neutrino background. Our most interesting result is that our adopted varying IMF leads to much greater uncertainty on the SFRD at $z \approx 2-4$ than is usually assumed. Indeed, we find a SFRD (inferred using observed galaxy luminosity distributions) that is a factor of $\gtrsim 3$ lower than canonical results obtained using a universal Salpeter-like IMF. Secondly, the non-universal IMF we explore implies a reduction in the supernova core-collapse rate of a factor of $\sim2$, compared against a universal IMF. The other potential tracers are only slightly affected by changes to the properties of the IMF. We find that currently available data do not provide a clear preference for universal or non-universal IMF. However, improvements to measurements of the star formation rate and core-collapse supernova rate at redshifts $z \gtrsim 2$ may offer the best prospects for discernment.

The presence of a super-light sterile neutrino can lead to a dip in the survival probability of solar neutrinos, and explain the suppression of the upturn in the low energy solar neutrino data. In this work, we systematically study the survival probabilities in the 3+1 framework by taking into account of the non-adiabatic transitions and the coherence effect. We obtain an analytic equation that can predict the position of the dip. We also place constraints on the parameter space of sterile neutrinos by using the latest Borexino and KamLAND data. We find that the low and high energy neutrino data at Borexino are sensitive to different regions in the sterile neutrino parameter space. In the case with only $\theta_{01}$ being nonzero, the $\rm{{}^{8}B}$ data sets the strongest bounds at $\Delta m_{01}^{2} \approx (1.1\sim2.2)\Delta m_{21}^{2}$, while the low energy neutrino data is more sensitive to other mass-squared regions. The lowest bounds on $\Delta m_{01}^{2}$ from the $\rm{pp}$ data can reach $10^{-12} \ \rm{eV^{2}}$ because of the coherence effect. Also, due to the presence of non-adiabatic transitions, the bounds in the range of $10^{-9} \ \textrm{eV}^{2} \lesssim \Delta m_{01}^{2} \lesssim 10^{-5} \ \textrm{eV}^{2}$ become weaker as $\Delta m_{01}^{2}$ or $\sin^{2}2\theta_{01}$ decreases. We also find that in the case with only $\theta_{02}$ or $\theta_{03}$ being nonzero, the low energy solar neutrino data set similar but weaker bounds as compared to the case with only $\theta_{01}$ being nonzero. However, the bounds from the high energy solar data and the KamLAND data are largely affected by the sterile mixing angles.

If ultralight $(\ll$ eV), bosonic dark matter couples to right handed neutrinos, active neutrino masses and mixing angles depend on the ambient dark matter density. When the neutrino Majorana mass, induced by the dark matter background, is small compared to the Dirac mass, neutrinos are "pseudo-Dirac" fermions that undergo oscillations between nearly degenerate active and sterile states. We present a complete cosmological history for such a scenario and find severe limits from a variety of terrestrial and cosmological observables. For scalar masses in the "fuzzy" dark matter regime ($\sim 10^{-20}$ eV), these limits exclude couplings of order $10^{-30}$, corresponding to Yukawa interactions comparable to the gravitational force between neutrinos and surpassing equivalent limits on time variation in scalar-induced electron and proton couplings.

Pulsar Timing Arrays (PTAs) are exceptionally sensitive detectors in the frequency band $\text{nHz} \lesssim f \lesssim \mu\text{Hz}$. Ultralight dark matter (ULDM), with mass in the range $10^{-23}\,\text{eV} \lesssim m_\phi \lesssim 10^{-20}\,\text{eV}$, is one class of DM models known to generate signals in this frequency window. While purely gravitational signatures of ULDM have been studied previously, in this work we consider two signals in PTAs which arise in presence of direct couplings between ULDM and ordinary matter. These couplings induce variations in fundamental constants, i.e., particle masses and couplings. These variations can alter the moment of inertia of pulsars, inducing pulsar spin fluctuations via conservation of angular momentum, or induce apparent timing residuals due to reference clock shifts. By using mock data mimicking current PTA datasets, we show that PTA experiments outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons. In the case of coupling to quarks or photons, we find that PTAs and atomic clocks set similar constraints. Additionally, we discuss how future PTAs can further improve these constraints, and detail the unique properties of these signals relative to the previously studied effects of ULDM on PTAs.

Ultralight bosons can affect the dynamics of spinning black holes (BHs) via superradiant instability, which can lead to a time evolution of the supermassive BH shadow. We study prospects for witnessing the superradiance-induced BH shadow evolution, considering ultralight vector and tensor fields. We introduce two observables sensitive to the shadow time-evolution: the shadow drift, and the variation in the azimuthal angle lapse associated to the photon ring autocorrelation. The two observables are shown to be highly complementary, depending on the observer's inclination angle. Focusing on the supermassive object Sgr A$^\star$ we show that both observables can vary appreciably over human timescales of a few years in the presence of superradiant instability, leading to signatures which are well within the reach of the Event Horizon Telescope for realistic observation times (but benefiting significantly from extended observation periods), and paving the way towards probing ultralight bosons in the $\sim 10^{-17}\,{\rm eV}$ mass range.

Precision measurements of neutrino oscillation parameters have provided a tremendous boost to the search for sub-leading effects due to several beyond the Standard Model scenarios in neutrino oscillation experiments. Among these, two of the well-studied scenarios are Lorentz violation (LV) and non-standard interactions (NSI), both of which can affect neutrino oscillations significantly. We point out that, at a long-baseline experiment where the neutrino oscillation probabilities can be well-approximated by using the line-averaged constant matter density, the effects of these two scenarios can mimic each other. This would allow the limits obtained at such an experiment on one of the above scenarios to be directly translated to the limits on the other scenario. However, for the same reason, it would be difficult to distinguish between LV and NSI at a long-baseline experiment. We show that the observations of atmospheric neutrinos, which travel a wide range of baselines and may encounter sharp density changes at the core-mantle boundary, can break this degeneracy. We observe that identifying neutrinos and antineutrinos separately, as can be done at INO-ICAL, can enhance the capability of atmospheric neutrino experiments to discriminate between these two new-physics scenarios.

The nuGeN experiment is aimed to investigate neutrino properties using antineutrinos from the reactor of the Kalinin Nuclear Power Plant. The experimental setup is located at about 11 meters from the center of the 3.1 GWth reactor core. Scattering of the antineutrinos from the reactor is detected with low energy threshold high purity germanium detector. Passive and active shieldings are used to suppress all kinds of backgrounds coming from surrounding materials and cosmic radiation. The description of the experimental setup together with the first results is presented. The data taken in regimes with reactor ON (94.50 days) and reactor OFF (47.09 days) have been compared. No significant difference between spectra of two data sets is observed, i.e. no positive signals for coherent elastic neutrino-nucleus scattering are detected. Under Standard Model assumptions about coherent neutrino scattering an upper limit on a quenching parameter k < 0.26 (90 \% C.L.) in germanium has been set.

In the current epoch of neutrino physics, many experiments are aiming for precision measurements of oscillation parameters. Thus, various new physics scenarios which alter the neutrino oscillation probabilities in matter deserve careful investigation. In this context, we study the effect of a vector leptoquark which induces non-standard neutrino interactions (NSI) that modify the oscillation probabilities of neutrinos in matter. We show that such interactions provide a relatively large value of NSI parameter $\varepsilon_{e \mu}$. Considering this NSI parameter, we successfully explain the recent discrepancy between the observed $\delta_{CP}$ results of T2K and NOvA.

The IceCube Neutrino Observatory at the South Pole has measured astrophysical neutrinos using through-going and starting events in the TeV to PeV energy range. The origin of these astrophysical neutrinos is still largely unresolved, and among their potential sources could be dark matter decay. Measurements of the astrophysical flux using muon neutrinos are in slight tension with starting event measurements. This tension is driven by an excess observed in the energy range of 40-200 TeV with respect to the through-going expectation. Previous works have considered the possibility that this excess may be due to heavy dark matter decay and have placed constraints using gamma-ray and neutrino data. However, these constraints are not without caveats since they rely on the modeling of the astrophysical neutrino flux and the sources of gamma-ray emission. In this work, we derive background-agnostic galactic and extragalactic constraints on decaying dark matter by considering Tibet AS$_\gamma$ data, Fermi-LAT diffuse data, and the IceCube high-energy starting event sample. For the gamma-ray limits, we investigate the uncertainties on secondary emission from electromagnetic cascades during propagation arising from the unknown intensity of the extragalactic background light. We find that such uncertainties amount to a variation of up to $\sim 55\%$ in the gamma-ray limits derived with extragalactic data. Our results imply that a significant fraction of the astrophysical neutrino flux could be due to dark matter and that ruling it out depends on the assumptions on the gamma-ray and neutrino background. The latter depends on the yet unidentified sources.

The progress of neutrino astronomy makes the precise measurement of the flavor ratio of high energy astronomical neutrinos (HANs) possible in the near future. Then matter effects and new physics effects on the flavor transition of HANs could be tested by the next-generation neutrino telescopes. In this paper we study matter effects in gas around the sources of HANs. The matter effects are dependent on both the decoherence schemes and the sources of neutrinos. We examine the predictions on the flavor ratio at Earth for typical sources with five decoherence schemes. For the adiabatic schemes, the matter effect is notable and may be identified in the special range of the electron density, irrespective of the production sources of HANs. Hence, the precise measurement of the flavor ratio would provide constrains on the propagation schemes and the matter parameter.

We update and improve past efforts to predict the leptonic Dirac CP-violating phase with models that predict perturbatively modified tribimaximal or bimaximal mixing. Simple perturbations are applied to both mixing patterns in the form of rotations between two sectors. By translating these perturbed mixing matrices to the standard parameterization for the neutrino mixing matrix we derive relations between the Dirac CP-phase and the oscillation angles. We use these relations together with current experimental results to constrain the allowed range for the CP-phase and determine its probability density. Furthermore, we elaborate on the prospects for future experiments probing on the perturbations considered in this work. We present a model with $A_4$ modular symmetry that is consistent with one of the described perturbed scenarios and successfully predicts current oscillation parameter data.

The extraction of the neutrino mass ordering is one of the major challenges in particle physics and cosmology, not only for its implications for a fundamental theory of mass generation in nature, but also for its decisive role in the scale of future neutrinoless double beta decay experimental searches. It has been recently claimed that current oscillation, beta decay and cosmological limits on the different observables describing the neutrino mass parameter space provide robust decisive Bayesian evidence in favor of the normal ordering of the neutrino mass spectrum [arXiv:2203.14247]. We further investigate these strong claims using a rich and wide phenomenology, with different sampling techniques of the neutrino parameter space. Contrary to the findings of Jimenez et al [arXiv:2203.14247], no decisive evidence for the normal mass ordering is found. Neutrino mass ordering analyses must rely on priors and parameterizations that are ordering-agnostic: robust results should be regarded as those in which the preference for the normal neutrino mass ordering is driven exclusively by the data, while we find a difference of up to a factor of 33 in the Bayes factors among the different priors and parameterizations exploited here. An ordering-agnostic prior would be represented by the case of parameterizations sampling over the two mass splittings and a mass scale, or those sampling over the individual neutrino masses via normal prior distributions only. In this regard, we show that the current significance in favor of the normal mass ordering should be taken as $2.7\sigma$ (i.e. moderate evidence), mostly driven by neutrino oscillation data.

The relic neutrinos from old supernova explosions are among the most ancient neutrino fluxes within experimental reach. Thus, the diffuse supernova neutrino background (DSNB) could teach us if neutrino masses were different in the past (redshifts $z\lesssim 5$). Oscillations inside the supernova depend strongly on the neutrino mass-squared differences and the values of the mixing angles, rendering the DSNB energy spectrum sensitive to variations of these parameters. Considering a purely phenomenological parameterization of the neutrino masses as a function of redshift, we compute the expected local DSNB spectrum here on Earth. Given the current knowledge of neutrino oscillation parameters, specially the fact that $|U_{e3}|^2$ is small, we find that the $\nu_e$ spectrum could be significantly different from standard expectations if neutrinos were effectively massless at $z\gtrsim1$ as long as the neutrino mass ordering is normal. On the other hand, the $\overline{\nu}_e$ flux is not expected to be significantly impacted. Hence, a measurement of both the neutrino and antineutrino components of the DSNB should allow one to test the possibility of recent neutrino mass generation.

In global analyses of nuclear parton distribution functions (nPDFs), neutrino deep-inelastic scattering (DIS) data have been argued to exhibit tensions with the data from charged-lepton DIS. Using the nCTEQ framework, we investigate these possible tensions both internally and with the data sets used in our recent nPDF analysis nCTEQ15WZSIH. We take into account nuclear effects in the calculation of the deuteron structure function $F_2^D$ using the CJ15 analysis. The resulting nPDF fit, nCTEQ15WZSIHdeut, serves as the basis for our comparison with inclusive neutrino DIS and charm dimuon production data. Using $\chi^2$ hypothesis testing, we confirm evidence of tensions with these data and study the impact of the proton PDF baseline as well as the treatment of data correlation and normalization uncertainties. We identify the experimental data and kinematic regions that generate the tensions and present several possible approaches how a consistent global analysis with neutrino data can be performed. We show that the tension can be relieved using a kinematic cut at low $x$ ($x>0.1$) and also investigate a possibility of managing the tensions by using uncorrelated systematic errors. Finally, we present a different approach identifying a subset of neutrino data which leads to a consistent global analysis without any additional cuts. Understanding these tensions between the neutrino and charged-lepton DIS data is important not only for a better flavor separation in global analyses of nuclear and proton PDFs, but also for neutrino physics and for searches for physics beyond the Standard Model.

One of the few remaining unknowns in the standard three-flavor neutrino oscillation paradigm is the ordering of neutrino masses. In this work we propose a novel method for determining neutrino mass ordering using the time information on early supernova neutrino events. In a core-collapse supernova, neutrinos are produced earlier than antineutrinos and, depending on the mass ordering which affects the adiabatic flavor evolution, may cause earlier observable signals in $\nu_e$ detection channels than in others. Hence, the time differences are sensitive to the mass ordering. We find that using the time information on the detection of the first galactic supernova events at future detectors like DUNE, JUNO and Hyper-Kamiokande, the mass ordering can already be determined at $\sim 2 \sigma$ CL, while $\mathcal{O}(10)$ events suffice for the discovery. Our method does not require high statistics and could be used within the supernova early warning system (SNEWS) which will have access to the time information on early supernova neutrino events recorded in a number of detectors. The method proposed in this paper also implies a crucial interplay between the mass ordering and the triangulation method for locating supernovae.

We present the sensitivity of the Theia experiment to low-energy geo- and reactor antineutrinos. For this study, we consider one of the possible proposed designs, a 17.8-ktonne fiducial volume Theia-25 detector filled with water-based liquid scintillator placed at Sanford Underground Research Facility (SURF). We demonstrate Theia's sensitivity to measure the geo- and reactor antineutrinos via Inverse-Beta Decay interactions after one year of data taking with $11.9\times10^{32}$ free target protons. The expected number of detected geo- and reactor antineutrinos is $218\,^{+28}_{-20}$ and $170\,^{+24}_{-20}$, respectively. The precision of the fitting procedure has been evaluated to be 6.72% and 8.55% for geo- and reactor antineutrinos, respectively. We also demonstrate the sensitivity towards fitting individual Th and U contributions, with best fit values of $N_\text{Th}=39\,^{+18}_{-15}$ and $N_\text{U}=180\,^{+26}_{-22}$. We obtain $(\text{Th}/\text{U})=4.3\pm2.6$ after one year of data taking, and within ten years, the relative precision of the (Th/U) mass ratio will be reduced to 15%. Finally, from the fit results of individual Th and U contributions, we evaluate the mantle signal to be $S_\text{mantle} = 9.0\,\pm [4.2,4.5]$NIU. This was obtained assuming a full-range positive correlation ($\rho_c\in[0, 1]$) between Th and U, and the projected uncertainties on the crust contributions of 8.3% (Th) and 7.0% (U). When considering systematic uncertainties on the signal and background shape and fluxes, the mantle signal becomes $S_\text{mantle} = 9.3\,\pm [5.2,5.4]$NIU.

We present a generic structure (the layer structure) for decoherence effects in neutrino oscillations, which includes decoherence from quantum mechanical and classical uncertainties. The calculation is done by combining the concept of open quantum system and quantum field theory, forming a structure composed of phase spaces from microscopic to macroscopic level. Having information loss at different levels, quantum mechanical uncertainties parameterize decoherence by an intrinsic mass eigenstate separation effect, while decoherence for classical uncertainties is typically dominated by a statistical averaging effect. With the help of the layer structure, we classify the former as state decoherence (SD) and the latter as phase decoherence (PD), then further conclude that both SD and PD result from phase wash-out effects of different phase structures on different layers. Such effects admit for simple numerical calculations of decoherence for a given width and shape of uncertainties. While our structure is generic, so are the uncertainties, nonetheless, a few notable ones are: the wavepacket size of the external particles, the effective interaction volume at production and detection, the energy reconstruction model and the neutrino production profile. Furthermore, we estimate the experimental sensitivities for SD and PD parameterized by the uncertainty parameters, for reactor neutrinos and decay-at-rest neutrinos, using a traditional rate measuring method and a novel phase measuring method.

Over the last several years, our understanding of neutrino oscillations has developed significantly due to the long-baseline measurements of muon-neutrino disappearance and muon-to-electron-neutrino appearance at the T2K and NOvA experiments. However, when interpreted under the standard-three-massive-neutrinos paradigm, a tension has emerged between the two experiments' data. Here, we examine whether this tension can be alleviated when a fourth, very light neutrino is added to the picture. Specifically, we focus on the scenario in which this new neutrino has a mass similar to, or even lighter than, the three mostly-active neutrinos that have been identified to date. We find that, for some regions of parameter space, the four-neutrino framework is favored over the three-neutrino one with moderate (a little under two sigma) significance. Interpreting these results, we provide future outlook for near-term and long-term experiments if this four-neutrino framework is indeed true.

In neutrino oscillation physics numerous exact degeneracies exist under the name LMA-Dark. These degeneracies make it impossible to determine the sign of $\Delta m^2_{31}$ known as the atmospheric mass ordering with oscillation experiments alone in the presence of new neutrino interactions. The combination of different measurements including multiple oscillation channels and neutrino scattering experiments lifts some aspects of these degeneracies. In fact, previous measurements of coherent elastic neutrino nucleus scattering (CEvNS) by COHERENT already ruled out the LMA-Dark solution for new physics with mediators heavier than $M_{Z'}\sim50$ MeV while cosmological considerations disfavor these scenarios for mediators lighter than $M_{Z'}\sim3$ MeV. Here we leverage new data from the Dresden-II experiment which provides the strongest bounds on CEvNS with reactor neutrinos to date. We show that this data completely removes the degeneracies in the $\nu_e$ sector for mediators down to the MeV scale at which point constraints from the early universe take over. While the LMA-Dark degeneracy is lifted in the $\nu_e$ sector, it can still be restored in the $\nu_\mu$ and $\nu_\tau$ sector or with very specific couplings to up and down quarks, and we speculate on a path forward.

Since the beginning of 2012, the Borexino collaboration has been reporting precision measurements of the solar neutrino fluxes, emitted in the proton-proton chain and in the Carbon-Nitrogen-Oxygen cycle. The experimental sensitivity achieved in Phase-II and Phase-III of the Borexino data taking made it possible to detect the annual modulation of the solar neutrino interaction rate due to the eccentricity of Earth's orbit, with a statistical significance greater than 5$\sigma$. This is the first precise measurement of the Earth's orbital parameters based solely on solar neutrinos and an additional signature of the solar origin of the Borexino signal. The complete periodogram of the time series of the Borexino solar neutrino detection rate is also reported, exploring frequencies between one cycle/year and one cycle/day. No other significant modulation frequencies are found. The present results were uniquely made possible by Borexino's decade-long high-precision solar neutrino detection.

We present compact analytic expressions for 3-flavor neutrino oscillation probabilities with invisible neutrino decay, where matter effects have been explicitly included. We take into account the possibility that the oscillation and decay components of the effective Hamiltonian do not commute. This is achieved by employing the techniques of inverse Baker-Campbell-Hausdorff (BCH) expansion and the Cayley-Hamilton theorem applied in the 3-flavor framework. If only the vacuum mass eigenstate $\nu_3$ decays, we show that the treatment of neutrino propagation may be reduced to an effective 2-flavor analysis in the One Mass Scale Dominance (OMSD) approximation. The oscillation probabilities for $P_{\mu\mu}$, $P_{ee}$, $P_{e\mu}$ and $P_{\mu e}$ -- relevant for reactor, long baseline and atmospheric neutrino experiments -- are obtained as perturbative expansions for the case of only $\nu_3$ decay, as well as for the more general scenario where all components of the decay matrix are non-zero. The analytic results thus obtained match the exact numerical results for constant density matter to a high precision and provide physical insights into possible effects of the decay of neutrinos as they propagate through Earth matter. We find that the effects of neutrino decay are most likely to be observable in $P_{\mu\mu}$. We also point out that at any long baseline, the oscillation dips in $P_{\mu\mu}$ can show higher survival probabilities in the case with decay than without decay, and explain this feature using our analytic approximations.

Core collapse of massive stars leads to different fates for various physical factors, which gives different spectra of the emitted neutrinos. We focus on the supernova relic neutrinos (SRNs) as a probe to investigate the stellar collapse fate. We present the SRN fluxes and event rate spectra at a detector for three resultant states after stellar core collapse, the typical mass neutron star, the higher mass neutron star, or the failed supernova forming a black hole, based on different nuclear equations of state. Then possible SRN fluxes are formed as mixtures of the three components. We also show the expected sensitivities at the next-generation water-based Cherenkov detectors, SK-Gd and Hyper-Kamiokande, as constraining the mixture fractions. This study provides a practical example of extracting astrophysical constraints through SRN measurement.

Sterile neutrinos can be produced in the early universe via interactions with their active counterparts. For small active-sterile mixing angles, thermal equilibrium with the standard model plasma is not reached and sterile neutrinos are only produced via flavor oscillations. We study in detail this regime, taking into account matter potentials and decoherence effects caused by elastic scatterings with the plasma. We find that resonant oscillations occurring at temperatures $T\lesssim 10\,\mathrm{GeV}$ lead to a significant enhancement of the sterile neutrino production rate. Taking this into account, we improve constraints on the active-sterile mixing from Big Bang nucleosynthesis and the cosmic microwave background, excluding mixing angles down to $\theta_s\sim 10^{-10}-10^{-16}$ for sterile neutrino masses in the $10\,\mathrm{MeV}$ to $10\,\mathrm{GeV}$ range. We observe that if sterile neutrinos predominantly decay into metastable hidden sector particles, this process provides a novel dark matter production mechanism, consistent with the sterile neutrino origin of light neutrino masses via the seesaw mechanism.

We present a detailed analysis of the spectral data of Borexino Phase II, with the aim of exploiting its full potential to constrain scenarios beyond the Standard Model. In particular, we quantify the constraints imposed on neutrino magnetic moments, neutrino non-standard interactions, and several simplified models with light scalar, pseudoscalar or vector mediators. Our analysis shows perfect agreement with those performed by the collaboration on neutrino magnetic moments and neutrino non-standard interactions in the same restricted cases and expands beyond those, stressing the interplay between flavour oscillations and flavour non-diagonal interaction effects for the correct evaluation of the event rates. For simplified models with light mediators we show the power of the spectral data to obtain robust limits beyond those previously estimated in the literature.

We study the impact of the interaction between DM and the cosmic neutrino background on the evolution of galactic dark matter halos. The energy transfer from the neutrinos to the dark matter can heat the center of the galaxy and make it cored. This effect is efficient for the small galaxies such as the satellite galaxies of the Milky Way and we can put conservative constraint on the non-relativistic elastic scattering cross section as $\sigma_{\chi\nu}\lesssim 10^{-31} {\rm cm}^2$ for 0.1 keV dark matter and 0.1 eV neutrino.

We compute the differential decay width of two- and three-body neutrino decays, assuming neutrinos are Dirac fermions and allowing for the possibility that the decay-daughters have nonzero masses. We examine different hypotheses for the interaction that mediates neutrino decay and concentrate on identifying circumstances where the decay-daughters can significantly impact the neutrino-decay signature at different experiments. We are especially interested in decay daughters produced by right-chiral neutrino fields, when the mass of the daughter plays a decisive role. As a concrete example, we compare the effects of visible and invisible antineutrino decays at the JUNO experimental setup.

The latest cosmological constraints on the sum of neutrino masses, in combination with the latest laboratory measurements on oscillations, provide ``decisive" Bayesian evidence for the normal neutrino mass hierarchy. We show that this result holds across very different prior alternatives by exploring two extremes on the range of prior choices. In fact, while the specific numerical value for the Evidence depends on the choice of prior, the Bayesian odds remain greater than 140:1 across very different prior choices. For Majorana neutrinos this has important implications for the upper limit of the neutrino-less double beta decay half life and thus for the technology and resources needed for future double beta decay experiments.

The observation of ultra-high-energy EeV-energy cosmogenic neutrinos provides a direct path to identifying the sources of the highest energy cosmic rays; searches have so far resulted in only upper limits on their flux. However, with the realization of cubic-kilometer detectors such as IceCube and, in the near future, KM3NeT, GVD-Baikal, and similar instruments, we anticipate the observation of PeV-energy cosmic neutrinos with high statistics. In this context, we draw attention to the opportunity to identify EeV tau neutrinos at PeV energy using Earth-traversing tau neutrinos. We show that Cherenkov detectors can improve their sensitivity to transient point sources by more than an order of magnitude by indirectly observing EeV tau neutrinos with initial energies that are nominally beyond their reach. This new technique also improves their sensitivity to the ultra-high-energy diffuse neutrino flux by up to a factor of two. Our work exemplifies how observing tau neutrinos at PeV energies provides an unprecedented reach to EeV fluxes.

We show that the Gallium anomaly can not be explained by CC-NSI.

Measuring core-collapse supernova neutrinos, both from individual supernovae within the Milky Way and from past core collapses throughout the Universe (the diffuse supernova neutrino background, or DSNB), is one of the main goals of current and next generation neutrino experiments. Detecting the heavy-lepton flavor (muon and tau types, collectively $\nu_x$) component of the flux is particularly challenging due to small statistics and large backgrounds. While the next galactic neutrino burst will be observed in a plethora of neutrino channels, allowing to measure a small number of $\nu_x$ events, only upper limits are anticipated for the diffuse $\nu_x$ flux even after decades of data taking with conventional detectors. However, paleo-detectors could measure the time-integrated flux of neutrinos from galactic core-collapse supernovae via flavor-blind neutral current interactions. In this work, we show how combining a measurement of the average galactic core-collapse supernova flux with paleo detectors and measurements of the DSNB electron-type neutrino fluxes with the next-generation water Cherenkov detector Hyper-Kamiokande and the liquid noble gas detector DUNE will allow to determine the mean supernova $\nu_x$ flux parameters with precision of order ten percent.

Non-Standard Interactions (NSI) between neutrinos and matter affect the neutrino flavor oscillations. Due to the high matter density in the core of the Sun, solar neutrinos are suited to probe these interactions. Using the $277$ kton-yr exposure of Super-Kamiokande to $^{8}$B solar neutrinos, we search for the presence of NSI. Our data favors the presence of NSI with down quarks at 1.8$\sigma$, and with up quarks at 1.6$\sigma$, with the best fit NSI parameters being ($\epsilon_{11}^{d},\epsilon_{12}^{d}$) = (-3.3, -3.1) for $d$-quarks and ($\epsilon_{11}^{u},\epsilon_{12}^{u}$) = (-2.5, -3.1) for $u$-quarks. After combining with data from the Sudbury Neutrino Observatory and Borexino, the significance increases by 0.1$\sigma$.

Neutrinos are one of the most promising messengers for signals of new physics Beyond the Standard Model (BSM). On the theoretical side, their elusive nature, combined with their unknown mass mechanism, seems to indicate that the neutrino sector is indeed opening a window to new physics. On the experimental side, several long-standing anomalies have been reported in the past decades, providing a strong motivation to thoroughly test the standard three-neutrino oscillation paradigm. In this Snowmass21 white paper, we explore the potential of current and future neutrino experiments to explore BSM effects on neutrino flavor during the next decade.

The chemical composition of the highest end of the ultra-high-energy cosmic ray spectrum is very hard to measure experimentally, and to this day it remains mostly unknown. Since the trajectories of ultra-high-energy cosmic rays are deflected in the magnetic field of the Galaxy by an angle that depends on their atomic number $Z$, it could be possible to indirectly measure $Z$ by quantifying the amount of such magnetic deflections. In this paper we show that, using the angular harmonic cross-correlation between ultra-high-energy cosmic rays and galaxies, we could effectively distinguish different atomic numbers with current data. As an example, we show how, if $Z=1$, the cross-correlation can exclude a $39\%$ fraction of Fe56 nuclei at $2\sigma$ for rays above $100\text{EeV}$.

We consider invisible neutrino decay $\nu_H \to \nu_l + \phi$ in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant for the cosmic microwave background (CMB) anisotropies. Improving on our previous work which assumed massless $\nu_l$ and $\phi$, we reinstate in this work the daughter neutrino mass $m_{\nu l}$ in a manner consistent with the experimentally determined neutrino mass splittings. We find that a nonzero $m_{\nu l}$ introduces a new phase space factor in the loss rate $\Gamma_{\rm T}$ proportional to $(\Delta m_\nu^2/m_{\nu_H}^2)^2$ in the limit of a small squared mass gap between the parent and daughter neutrinos, i.e., $\Gamma_{\rm T} \sim (\Delta m_\nu^2/m_{\nu H}^2)^2 (m_{\nu H}/E_\nu )^5 (1/\tau_0)$, where $\tau_0$ is the $\nu_H$ rest-frame lifetime. Using a general form of this result, we update the limit on $\tau_0$ using the Planck 2018 CMB data. We find that for a parent neutrino of mass $m_{\nu H} \lesssim 0.1 {\rm eV}$, the new phase space factor weakens the constraint on its lifetime by up to a factor of 50 if $\Delta m_\nu^2$ corresponds to the atmospheric mass gap and up to $10^{5}$ if the solar mass gap, in comparison with naive estimates that assume $m_{\nu l}=0$. The revised constraints are (i) $\tau^0 \gtrsim (6 \to 10) \times 10^5~{\rm s}$ and $\tau^0 \gtrsim (400 \to 500)~{\rm s}$ if only one neutrino decays to a daughter neutrino separated by, respectively, the atmospheric and the solar mass gap, and (ii) $\tau^0 \gtrsim (2 \to 3) \times 10^7~{\rm s}$ in the case of two decay channels with one near-common atmospheric mass gap. In contrast to previous, naive limits which scale as $m_{\nu H}^5$, these mass spectrum-consistent $\tau_0$ constraints are remarkably independent of the parent mass and open up a swath of parameter space within the projected reach of IceCube and other neutrino telescopes in the next two decades.

Tau neutrinos are the least studied particle in the Standard Model. This whitepaper discusses the current and expected upcoming status of tau neutrino physics with attention to the broad experimental and theoretical landscape spanning long-baseline, beam-dump, collider, and astrophysical experiments. This whitepaper was prepared as a part of the NuTau2021 Workshop.

The Dresden-II reactor experiment has recently reported a suggestive evidence for the observation of coherent elastic neutrino-nucleus scattering, using a germanium detector. Given the low recoil energy threshold, these data are particularly interesting for a low-energy determination of the weak mixing angle and for the study of new physics leading to spectral distortions at low momentum transfer. Using two hypotheses for the quenching factor, we study the impact of the data on: (i) The weak mixing angle at a renormalization scale of $\sim 10\,\text{MeV}$, (ii) neutrino generalized interactions with light mediators, (iii) the sterile neutrino dipole portal. The results for the weak mixing angle show a strong dependence on the quenching factor choice. Although still with large uncertainties, the Dresden-II data provide for the first time a determination of $\sin^2\theta_W$ at such scale using coherent elastic neutrino-nucleus scattering data. Tight upper limits are placed on the light vector, scalar and tensor mediator scenarios. Kinematic constraints implied by the reactor anti-neutrino flux and the ionization energy threshold allow the sterile neutrino dipole portal to produce up-scattering events with sterile neutrino masses up to $\sim 8\,$MeV. In this context, we find that limits are also sensitive to the quenching factor choice, but in both cases competitive with those derived from XENON1T data and more stringent that those derived with COHERENT data, in the same sterile neutrino mass range.

The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta ($0\nu\beta\beta$) decay half-life in $^{136}$Xe using a xenon-loaded liquid scintillator. We report an improved search using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of $^{136}$Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the $0\nu\beta\beta$ decay half-life of $T_{1/2}^{0\nu} > 2.3 \times 10^{26}$ yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.

Time of flight delay in the supernova neutrino signal offers a unique tool to set model-independent constraints on the absolute neutrino mass. The presence of a sharp time structure during a first emission phase, the so-called neutronization burst in the electron neutrino flavor time distribution, makes this channel a very powerful one. Large liquid argon underground detectors will provide precision measurements of the time dependence of the electron neutrino fluxes. We derive here a new $\nu$ mass sensitivity attainable at the future DUNE far detector from a future supernova collapse in our galactic neighborhood, finding a sub-eV reach under favorable scenarios. These values are competitive with those expected for laboratory direct neutrino mass searches.

Theia would be a novel, "hybrid" optical neutrino detector, with a rich physics program. This paper is intended to provide a brief overview of the concepts and physics reach of Theia. Full details can be found in the Theia white paper [1].

The renormalization-group equation (RGE) approach to neutrino matter effects is further developed in this work. We derive a complete set of differential equations for effective mixing elements, masses and Jarlskog-like invariants in presence of a light sterile neutrino. The evolutions of mixing elements as well as Jarlskog-like invariants are obtained by numerically solving these differential equations. We calculate terrestrial matter effects in long-baseline (LBL) experiments, taking NOvA, T2K and DUNE as examples. In both three-flavor and four-flavor frameworks, electron-neutrino survival probabilities as well as the day-night asymmetry of solar neutrino are also evaluated as a further examination of the RGE approach.

We explore the possibility of using the recently proposed THEIA detector to measure the $\bar \nu_\mu \rightarrow \bar \nu_e$ oscillation with neutrinos from a muon decay at rest ($\mu$DAR) source to improve the leptonic CP phase measurement. Due to its intrinsic low-energy beam, this $\mu$THEIA configuration ($\mu$DAR neutrinos at THEIA) is only sensitive to the genuine leptonic CP phase $\delta_D$ and not contaminated by the matter effect. With detailed study of neutrino energy reconstruction and backgrounds at the THEIA detector, we find that the combination with the high-energy DUNE can significantly reduce the CP uncertainty, especially around the maximal CP violation cases $\delta_D = \pm 90^\circ$. Both the $\mu$THEIA-25 with 17kt and $\mu$THEIA-100 with 70kt fiducial volumes are considered. For DUNE + $\mu$THEIA-100, the CP uncertainty can be better than $8^\circ$.

As low-threshold dark matter detectors advance in development, they will become sensitive to recoils from solar neutrinos which opens up the possibility to explore neutrino properties. We predict the enhancement of the event rate of solar neutrino scattering from Beyond the Standard Model interactions in low-threshold DM detectors, with a focus on silicon, germanium, gallium arsenide, xenon, and argon-based detectors. We consider a set of general neutrino interactions, which fall into five categories: the neutrino magnetic moment as well as interactions mediated by four types of mediators (scalar, pseudoscalar, vector, and axial vector), and consider coupling these mediators to either quarks or electrons. Using these predictions, we place constraints on the mass and couplings of each mediator and the neutrino magnetic moment from current low-threshold detectors like SENSEI, Edelweiss, and SuperCDMS, as well as projections relevant for future experiments such as DAMIC-M, Oscura, Darwin, and ARGO. We find that such low-threshold detectors can improve current constraints by up to two orders of magnitude for vector mediators and one order of magnitude for scalar mediators.

The ultimate objectives of ongoing and upcoming neutrino experiments are the precise measurement of neutrino mixing parameters and the confirmation of mass hierarchy. The systematic inaccuracy in the cross-section models introduces inaccuracy in the neutrino mixing parameters estimation. It is important to secure a large decrease of uncertainties, particularly those relating to cross-section, neutrino-nucleus interactions, and neutrino-energy reconstruction, in order to achieve these ambitious goals. In this research article, we use three alternative neutrino event generators, GENIE, NuWro, and GiBUU, to analyze sensitivity studies of T2HK, DUNE, and combined sensitivity of DUNE, and T2HK for mass hierarchy, CP violation, and octant degeneracy caused by cross-section uncertainties. The cross-section models of these generators are separate and independent.

Non-local correlations in entangled systems are usually captured by measures such as Bell's inequality violation. It was recently shown that in neutrino systems, a measure of non-local advantage of quantum coherence (NAQC) can be considered as a stronger measure of non-local correlations as compared to the Bell's inequality violation. In this work, we analyze the effects of non standard interaction (NSI) on these measures in the context of two flavour neutrino oscillations for DUNE, MINOS, T2K, KamLAND, JUNO and Daya Bay experimental set-ups. We find that even in the presence of NSI, Bell's inequality violation occurs in the entire energy range whereas the NAQC violation is observed only in some specific energy range justifying the more elementary feature of NAQC. Further, we find that NSI can enhance the violation of NAQC and Bell's inequality parameter in the higher energy range of a given experimental set-up; these enhancements being maximal for the KamLAND experiment. However, the possible enhancement in the violation of the Bell's inequality parameter over the standard model prediction can be up to 11% whereas for NAQC it is 7%. Thus although NAQC is a comparatively stronger witness of nonclassicality, it shows lesser sensitivity to NSI effects in comparison to the Bell's inequality parameter.

Light sterile neutrinos have been motivated by anomalies observed in short-baseline neutrino experiments.Among them, radioactive-source and reactor experiments have provided evidence and constraints, respectively, for electron neutrino disappearance compatible with an eV-scale neutrino. The results from these observations are seemingly in conflict. This letter brings into focus the assumption that the neutrino wave packet can be approximated as a plane wave, which is adopted in all analyses of such experiments. We demonstrate that the damping of oscillations, e.g., due to a finite wave packet size, solve the tension between these electron-flavor observations and constraints.

Dark matter (DM) direct detection experiments are entering the multiple-ton era and will be sensitive to the coherent elastic neutrino nucleus scattering (CE$\nu$NS) of solar neutrinos, enabling the possibility to explore contributions from new physics with light mediators at the low energy range. In this paper we consider light mediator models (scalar, vector and axial vector) and the corresponding contributions to the solar neutrino CE$\nu$NS process. Motivated by the current status of new generation of DM direct detection experiments and the future plan, we study the sensitivity of light mediators in DM direct detection experiments of different nuclear targets and detector techniques. The constraints from the latest $^8$B solar neutrino measurements of XENON-1T are also derived. Finally, We show that the solar neutrino CE$\nu$NS process can provide stringent limitation on the $ L_{\mu}-L_{\tau} $ model with the vector mediator mass below 100 MeV, covering the viable parameter space of the solution to the $ (g-2)_{\mu}$ anomaly.

We report a search for nonstandard neutrino interactions (NSI) using eight years of TeV-scale atmospheric muon neutrino data from the IceCube Neutrino Observatory. By reconstructing incident energies and zenith angles for atmospheric neutrino events, this analysis presents unified confidence intervals for the NSI parameter $\epsilon_{\mu \tau}$. The best-fit value is consistent with no NSI at a p-value of 25.2%. With a 90% confidence interval of $-0.0041 \leq \epsilon_{\mu \tau} \leq 0.0031$ along the real axis and similar strength in the complex plane, this result is the strongest constraint on any NSI parameter from any oscillation channel to date.

This letter presents the results from the MiniBooNE experiment within a full "3+1" scenario where one sterile neutrino is introduced to the three-active-neutrino picture. In addition to electron-neutrino appearance at short-baselines, this scenario also allows for disappearance of the muon-neutrino and electron-neutrino fluxes in the Booster Neutrino Beam, which is shared by the MicroBooNE experiment. We present the 3+1 fit to the MiniBooNE electron-(anti)neutrino and muon-(anti)neutrino data alone, and in combination with MicroBooNE electron-neutrino data. The best-fit parameters of the combined fit with the exclusive CCQE analysis (inclusive analysis) are $\Delta m^2 = 0.29 eV^2 (0.33 eV^2)$, $|U_{e4}|^2 = 0.016 (0.500)$, $|U_{\mu 4}|^2 = 0.500 (0.500)$, and $\sin^2(2\theta_{\mu e})=0.0316 (1.0)$. Comparing the no-oscillation scenario to the 3+1 model, the data prefer the 3+1 model with a $\Delta \chi^2/\text{dof} = 24.7 / 3 (17.3 / 3)$, a $4.3\sigma (3.4\sigma)$ preference assuming the asymptotic approximation given by Wilks' theorem.

Non-standard interactions of neutrinos arising in many theories beyond the Standard Model can significantly alter matter effects in atmospheric neutrino propagation through the Earth. In this paper, a search for deviations from the prediction of the standard 3-flavour atmospheric neutrino oscillations using the data taken by the ANTARES neutrino telescope is presented. Ten years of atmospheric neutrino data collected from 2007 to 2016, with reconstructed energies in the range from $\sim$16 GeV to $100$ GeV, have been analysed. A log-likelihood ratio test of the dimensionless coefficients $\varepsilon_{\mu\tau}$ and $\varepsilon_{\tau\tau} - \varepsilon_{\mu\mu}$ does not provide clear evidence of deviations from standard interactions. For normal neutrino mass ordering, the combined fit of both coefficients yields a value 1.7$\sigma$ away from the null result. However, the 68% and 95% confidence level intervals for $\varepsilon_{\mu\tau}$ and $\varepsilon_{\tau\tau} - \varepsilon_{\mu\mu}$, respectively, contain the null value. Best fit values, one standard deviation errors and bounds at the 90% confidence level for these coefficients are given for both normal and inverted mass orderings. The constraint on $\varepsilon_{\mu\tau}$ is among the most stringent to date and it further restrains the strength of possible non-standard interactions in the $\mu - \tau$ sector.

We study damping signatures at the Jiangmen Underground Neutrino Observatory (JUNO), a medium-baseline reactor neutrino oscillation experiment. These damping signatures are motivated by various new physics models, including quantum decoherence, $\nu_3$ decay, neutrino absorption, and wave packet decoherence. The phenomenological effects of these models can be characterized by exponential damping factors at the probability level. We assess how well JUNO can constrain these damping parameters and how to disentangle these different damping signatures at JUNO. Compared to current experimental limits, JUNO can significantly improve the limits on $\tau_3/m_3$ in the $\nu_3$ decay model, the width of the neutrino wave packet $\sigma_x$, and the intrinsic relative dispersion of neutrino momentum $\sigma_{\rm rel}$.

Atmospheric neutrinos offer the possibility of probing dark matter inside the core of the Earth in a unique way, through Earth matter effects in neutrino oscillations. For example, if dark matter constitutes 40% of the mass inside the core, a detector like ICAL at INO with muon charge identification capability can be sensitive to it at around 2$\sigma$ confidence level with 1000 kt$\cdot$yr exposure. We demonstrate that while the dark matter profile will be hard to identify, the baryonic matter profile inside the core can be probed in a manner complementary to the seismic measurements.

We present cosmological constraints on the sum of neutrino masses as a function of the neutrino lifetime, in a framework in which neutrinos decay into dark radiation after becoming non-relativistic. We find that in this regime the cosmic microwave background (CMB), baryonic acoustic oscillations (BAO) and (uncalibrated) luminosity distance to supernovae from the Pantheon catalog constrain the sum of neutrino masses $\sum m_\nu$ to obey $\sum m_\nu< 0.42$ eV at (95$\%$ C.L.). While the the bound has improved significantly as compared to the limits on the same scenario from Planck 2015, it still represents a significant relaxation of the constraints as compared to the stable neutrino case. We show that most of the improvement can be traced to the more precise measurements of low-$\ell$ polarization data in Planck 2018, which leads to tighter constraints on $\tau_{\rm reio}$ (and thereby on $A_s$), breaking the degeneracy arising from the effect of (large) neutrino masses on the amplitude of the CMB power spectrum.

Searches for neutrino magnetic moments/transitions in low energy neutrino scattering experiments are sensitive to effective couplings which are an intricate function of the Hamiltonian parameters. We study the parameter space dependence of these couplings in the Majorana (transitions) and Dirac (moments) cases, as well as the impact of the current most stringent experimental upper limits on the fundamental parameters. In the Majorana case we find that for reactor, short-baseline and solar neutrinos, CP violation can be understood as a measurement of parameter space vectors misalignments. The presence of nonvanishing CP phases opens a blind spot region where -- regardless of how large the parameters are -- no signal can be observed in either reactor or short-baseline experiments. Identification of these regions requires a combination of different data sets and allows for the determination of those CP phases. We point out that stringent bounds not necessarily imply suppressed Hamiltonian couplings, thus allowing for regions where disparate upper limits can be simultaneously satisfied. In contrast, in the Dirac case stringent experimental upper limits necessarily translate into tight bounds on the fundamental couplings. In terms of parameter space vectors, we provide a straightforward mapping of experimental information into parameter space.

The phenomenon of fully coherent energy loss (FCEL) in the collisions of protons on light ions affects the physics of cosmic ray air showers. As an illustration, we address two closely related observables: hadron production in forthcoming proton-oxygen collisions at the LHC, and the atmospheric neutrino fluxes induced by the semileptonic decays of hadrons produced in proton-air collisions. In both cases, a significant nuclear suppression due to FCEL is predicted. The conventional and prompt neutrino fluxes are suppressed by $\sim 10...25\%$ in their relevant neutrino energy ranges. Previous estimates of atmospheric neutrino fluxes should be scaled down accordingly to account for FCEL.

The Galactic center excess (GCE) remains one of the most intriguing discoveries from the Fermi Large Area Telescope (LAT) observations. We revisit the characteristics of the GCE by first producing a new set of high-resolution galactic diffuse gamma-ray emission templates, which are ultimately due to cosmic-ray interactions with the interstellar medium. Using multi-messenger observations we constrain the properties of the galactic diffuse emission. The broad properties of the GCE that we find in this work are qualitatively unchanged despite the introduction of this new set of templates, though its quantitative features appear mildly different than those obtained in previous analyses. In particular, we find a high-energy tail at higher significance than previously reported. This tail is very prominent in the northern hemisphere, and less so in the southern hemisphere. This strongly affects one prominent interpretation of the excess: known millisecond pulsars are incapable of producing this high-energy emission, even in the relatively softer southern hemisphere, and are therefore disfavored as the sole explanation of the GCE. The annihilation of dark matter particles of mass $40^{+10}_{-7}$ GeV (95$\%$ CL) to $b$ quarks with a cross-section of $\sigma v = 1.4^{+0.6}_{-0.3} \times 10^{-26}$ cm$^{3}$s$^{-1}$ provides a good fit to the excess especially in the relatively cleaner southern sky. Dark matter of the same mass range annihilating to $b$ quarks or heavier dark matter particles annihilating to heavier Standard Model bosons can combine with millisecond pulsars to provide a good fit to the southern hemisphere emission. As part of this paper, we make publicly available all of our templates and the data covariance matrix we have generated to account for systematic uncertainties.[abridged]

We systematically investigate new physics scenarios that can modify the interactions between neutrinos and matter at upcoming tau neutrino telescopes, which will test neutrino-proton collisions with energies $ \gtrsim 45~{\rm TeV}$, and can provide unique insights to the elusive tau neutrino. At such high energy scales, the impact of parton distribution functions of second and third generations of quarks (usually suppressed) can be comparable to the contribution of first generation with small momentum fraction, hence making tau neutrino telescopes an excellent facility to probe new physics associated with second and third families. Among an inclusive set of particle physics models, we identify new physics scenarios at tree level that can give competitive contributions to the neutrino cross sections while staying within laboratory constraints: charged/neutral Higgs and leptoquarks. Our analysis is close to the actual experimental configurations of the telescopes, and we perform a $\chi^2$-analysis on the energy and angular distributions of the tau events. By numerically solving the propagation equations of neutrino and tau fluxes in matter, we obtain the sensitivities of representative upcoming tau neutrino telescopes, GRAND, POEMMA and Trinity, to the charged Higgs and leptoquark models. While each of the experiments can achieve a sensitivity better than the current collider reaches for certain models, their combination is remarkably complementary in probing the new physics. In particular, the new physics will affect the energy and angular distributions in different ways at those telescopes.

Fully understanding the average core-collapse supernova requires detecting the diffuse supernova neutrino background (DSNB) in all flavors. While the DSNB $\bar{\nu}_e$ flux is near detection, and the DSNB $\nu_e$ flux has a good upper limit and prospects for improvement, the DSNB $\nu_x$ (each of $\nu_\mu, \nu_\tau, \bar{\nu}_\mu, \bar{\nu}_\tau$) flux has a poor limit and heretofore had no clear path for improved sensitivity. We show that a succession of xenon-based dark matter detectors -- XENON1T (completed), XENONnT/LUX-ZEPLIN (running), and DARWIN (proposed) -- can dramatically improve sensitivity to DSNB $\nu_x$ the neutrino-nucleus coherent scattering channel. XENON1T could match the present sensitivity of $\sim 10^3 \; \mathrm{cm}^{-2}~\mathrm{s}^{-1}$ per $\nu_x$ flavor, XENONnT/LUX-ZEPLIN would have linear improvement of sensitivity with exposure, and a long run of DARWIN could reach a flux sensitivity of $\sim 10 \; \mathrm{cm}^{-2}~\mathrm{s}^{-1}$. Together, these would also contribute to greatly improve bounds on non-standard scenarios. Ultimately, to reach the standard flux range of $\sim 1 \; \mathrm{cm}^{-2}~\mathrm{s}^{-1}$, even larger exposures will be needed, which we show may be possible with the series of proposed lead-based RES-NOVA detectors.

We discuss time reversal (T) violation in neutrino oscillations in generic new physics scenarios. A general parameterization is adopted to describe flavour evolution, which captures a wide range of new physics effects, including non-standard neutrino interactions, non-unitarity, and sterile neutrinos in a model-independent way. In this framework, we discuss general properties of time reversal in the context of long-baseline neutrino experiments. Special attention is given to fundamental versus environmental T violation in the presence of generic new physics. We point out that T violation in the disappearance channel requires new physics which modifies flavour mixing at neutrino production and detection. We use time-dependent perturbation theory to study the effect of non-constant matter density along the neutrino path, and quantify the effects for the well studied baselines of the DUNE, T2HK, and T2HKK projects. The material presented here provides the phenomenological background for the model-independent test of T violation proposed by us in Ref. [1].

During the run III of the LHC, the forward experiments FASER$\nu$ and SND@LHC will be able to detect the Charged Current (CC) interactions of the high energy neutrinos of all three flavors produced at the ATLAS Interaction Point (IP). This opportunity may unravel mysteries of the third generation leptons. We build three models that can lead to a tau excess at these detectors through the following Lepton Flavor Violating (LFV) beyond Standard Model (SM) processes: (1) $\pi^+ \to \mu^+ \nu_\tau$; (2) $\pi^+ \to \mu^+ \bar{\nu}_\tau$ and (3) $\nu_e+{\rm nucleus}\to \tau +X$. We comment on the possibility of solving the $(g-2)_\mu$ anomaly and the $\tau$ decay anomalies within these models. We study the potential of the forward experiments to discover the $\tau$ excess or to constrain these models in case of no excess. We then compare the reach of the forward experiments with that of the previous as well as next generation experiments such as DUNE. We also discuss how the upgrade of FASER$\nu$ can distinguish between these models by studying the energy spectrum of the tau.

High-energy muon- and electron-neutrinos yield a non-negligible flux of tau neutrinos as they propagate through Earth. In this letter, we address the impact of this additional component in the PeV and EeV energy regimes for the first time. This contribution is predicted to be significantly larger than the atmospheric background above 300 TeV, and alters current and future neutrino telescopes' capabilities to discover a cosmic tau-neutrino flux. Further we demonstrate that Earthskimming neutrino experiments, designed to observe tau neutrinos, will be sensitive to cosmogenic neutrinos even in extreme scenarios without a primary tau-neutrino component.

We discuss correlations between the $\nu$SM CP phase $\delta$ and the phases that originate from new physics which causes neutrino-sector unitarity violation (UV) at low energies. This study is motivated to provide one of the building pieces for a machinery to diagnose non-unitarity, our ultimate goal. We extend the perturbation theory of neutrino oscillation in matter proposed by Denton {\it et al.}~(DMP) to include the UV effect expressed by the $\alpha$ parametrization. By analyzing the DMP-UV perturbation theory to first order, we are able to draw a completed picture of the $\delta$ - UV phase correlations in the whole kinematical region covered by the terrestrial neutrino experiments. There exist the two regions with the characteristically different patterns of the correlations: (1) the chiral-type $[e^{- i \delta } \alpha_{\mu e}, ~e^{ - i \delta} \alpha_{\tau e}, ~\alpha_{\tau \mu}]$ (PDG convention) correlation in the entire high-energy region $\vert \rho E \vert \gsim 6~(\text{g/cm}^3)$ GeV, and (2) (blobs of the $\alpha$ parameters) - $e^{ \pm i \delta}$ correlation in anywhere else. Some relevant aspects for measurement of the UV parameters, such as the necessity of determining all the $\alpha_{\beta \gamma}$ elements at once, are also pointed out.

An ultralight dark matter may have interesting implications in neutrino physics which have been studied actively in recent years. It is pointed out that there appears yet unexplored medium effect in neutrino transitions which occurs at the first order in perturbation of the neutrino-medium interaction. We derive the general formula for the neutrino transition probability in a medium which describes the standard neutrino oscillation as well as the new medium contribution. It turns out that such an effect constrains the model parameter space more than ever.

The measurements of Cosmic Microwave Background anisotropies made by the Planck satellite provide extremely tight upper bounds on the total neutrino mass scale ($\Sigma m_{\nu}<0.26 eV$ at $95\%$ C.L.). However, as recently discussed in the literature, Planck data show anomalies that could affect this result. Here we provide new constraints on neutrino masses using the recent and complementary CMB measurements from the Atacama Cosmology Telescope DR4 and the South Polar Telescope SPT-3G experiments. We found that both the ACT-DR4 and SPT-3G data, when combined with WMAP, mildly suggest a neutrino mass with $\Sigma m_{\nu}=0.68 \pm 0.31$ eV and $\Sigma m_{\nu}=0.46_{-0.36}^{+0.14}$ eV at $68 \%$ C.L, respectively. Moreover, when CMB lensing from the Planck experiment is included, the ACT-DR4 data now indicates a neutrino mass above the two standard deviations, with $\Sigma m_{\nu}=0.60_{-0.50}^{+0.44}$ eV at $95 \%$, while WMAP+SPT-3G provides a weak upper limit of $\Sigma m_{\nu}<0.37$ eV at $68 \%$ C.L.. Interestingly, these results are consistent with the Planck CMB+Lensing constraint of $\Sigma m_{\nu} = 0.41_{-0.25}^{+0.17}$ eV at $68 \%$ C.L. when variation in the $A_{\rm lens}$ parameter are considered. We also show that these indications are still present after the inclusion of BAO or SN-Ia data in extended cosmologies that are usually considered to solve the so-called Hubble tension. A combination of ACT-DR4, WMAP, BAO and constraints on the Hubble constant from the SH0ES collaboration gives $\Sigma m_{\nu}=0.39^{+0.13}_{-0.25}$ eV at $68 \%$ C.L. in extended cosmologies. We conclude that a total neutrino mass above the $0.26$ eV limit still provides an excellent fit to several cosmological data and that future data must be considered before safely ruling it out.