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![The final MiniBooNE allowed regions for the full fit of all neutrino and antineutrino running mode data. Reproduced from [33]. CC BY 4.0.](publication/385371806/figure/fig3/AS:11431281307799665@1738718118290/The-final-MiniBooNE-allowed-regions-for-the-full-fit-of-all-neutrino-and-antineutrino.jpg)
The final MiniBooNE allowed regions for the full fit of all neutrino and antineutrino running mode data. Reproduced from [33]. CC BY 4.0.
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Citations
... These attributes have enabled reactor-based experiments to perform world-leading three-neutrino-flavor oscillation measurements [1][2][3][4][5][6]. Likewise, reactors are uniquely PHYSICAL REVIEW LETTERS 134, 151802 (2025) 0031-9007=25=134(15)=151802 (7) 151802-1 Published by the American Physical Society positioned in the global effort to understand the origins of observations that suggest the existence of short-baseline neutrino flavor transformation [7][8][9]. A simple model often used to fit these anomalies posits an additional sterile neutrino state of roughly eV-scale mass difference with respect to the known neutrino flavors [10], referred to as a "3 þ 1" model. ...
... These attributes have enabled reactor-based experiments to perform world-leading three-neutrino-flavor oscillation measurements [1][2][3][4][5][6]. Likewise, reactors are uniquely positioned in the global effort to understand the origins of observations that suggest the existence of short-baseline neutrino flavor transformation [7][8][9]. ...
... The new mass state in a 3 þ 1 model could also generate transitions of accelerator-produced muon flavor neutrinos to electron flavor [13][14][15]. However, this simple BSM scenario cannot be reconciled with an array of accelerator [16][17][18], reactor [19][20][21][22][23], atmospheric [24], and weak decay [25] experimental results, which has prompted a wide range of subsequent phenomenological investigation [8]. ...
The PROSPECT experiment is designed to perform precise searches for antineutrino disappearance at short distances (7–9 m) from compact nuclear reactor cores. This Letter reports results from a new neutrino oscillation analysis performed using the complete data sample from the PROSPECT-I detector operated at the High Flux Isotope Reactor in 2018. The analysis uses a multiperiod selection of inverse beta decay neutrino interactions with reduced backgrounds and enhanced statistical power to set limits on electron neutrino disappearance caused by mixing with sterile neutrinos with 0.2 – 20 eV 2 mass splittings. Inverse beta decay positron energy spectra from six different reactor-detector distance ranges are found to be statistically consistent with one another, as would be expected in the absence of sterile neutrino oscillations. The data excludes at 95% confidence level the existence of sterile neutrinos in regions above 3 eV 2 previously unexplored by terrestrial experiments, including all space below 10 eV 2 suggested by the recently strengthened Gallium Anomaly. The best-fit point of the Neutrino-4 reactor experiment’s claimed observation of short-baseline oscillation is ruled out at more than 5 standard deviations.
Published by the American Physical Society 2025
... This was revisited and understood better in the context of the spontaneously broken local hidden symmetry formalism [52]. However, it was later recognized that this channel's contribution to the NC single-photon production rate is too smallsmaller than contributions from ∆ resonances [53,54] (see also [55,56]). Nevertheless, the topology of this 2 → 3 scattering process and its resulting signature offer valuable insights that can help guide a new interpretation of the excess. ...
We propose new solutions to accommodate both the MiniBooNE electron-like and MicroBooNE photon low-energy excesses, based on interactions involving light dark matter and/or neutrinos. The novelty of our proposal lies in the utilization of a photon arising from 2-to-3 scattering processes between a nucleus/nucleon and a neutrino and/or dark matter via exchanges of light mediators. We find that viable regions exist in the coupling and mass parameter space of the mediators and light dark matter that can simultaneously explain the observed excesses and remain consistent with current experimental constraints. We further highlight that these scenarios can be tested with upcoming data from various ongoing experiments.
... [8][9][10] and the references cited therein. As a guide for reaching the further references beyond, we just cite ref. [20]. ...
A bstract
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 ∆ m 41 2 , 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 → ν e ), P ( ν ¯ e → ν ¯ e ), and P ( ν ¯ μ → ν ¯ τ ), and a three-component fit is suggested to disentangle the SA resonance generation mechanisms.
... 3+N. In this case, SBN could provide enhanced sensitivity to 3+2 and 3+3 short-baseline parameter space through multi-channel oscillation searches, as well as sensitivity to leptonic CP violation that may associated with an extended light sterile neutrino sector [42,43]. ...
SBND is a 112 ton liquid argon time projection chamber (LArTPC) neutrino detector located 110 meters from the Booster Neutrino Beam (BNB) target at Fermilab. Its main goals include searches for eV-scale sterile neutrinos as part of the Short-Baseline Neutrino (SBN) program, other searches for physics beyond the Standard Model, and precision studies of neutrino-argon interactions. In addition, SBND is providing a platform for LArTPC neutrino detector technology development and is an excellent training ground for the international group of scientists and engineers working towards the upcoming flagship Deep Underground Neutrino Experiment (DUNE). SBND began operation in July 2024, and started collecting stable neutrino beam data in December 2024 with an unprecedented rate of ~7,000 neutrino events per day. During its currently approved operation plans (2024-2027), SBND is expected to accumulate nearly 10 million neutrino interactions. The near detector dataset will be instrumental in testing the sterile neutrino hypothesis with unprecedented sensitivity in SBN and in probing signals of beyond the Standard Model physics. It will also be used to significantly advance our understanding of the physics of neutrino-argon interactions ahead of DUNE. After the planned accelerator restart at Fermilab (2029+), opportunities are being explored to operate SBND in antineutrino mode in order to address the scarcity of antineutrino-argon scattering data, or in a dedicated beam-dump mode to significantly enhance sensitivity to searches for new physics. SBND is an international effort, with approximately 40% of institutions from Europe, contributing to detector construction, commissioning, software development, and data analysis. Continued European involvement and leadership are essential during SBND's operations and analysis phase for both the success of SBND, SBN and its role leading up to DUNE.
... Diagonalizing the mass matrix of the neutrinos gives rise to an extended Pontecorvo-Maki-Nakagawa-Sakata mixing matrix that includes the elements U e;μ;τ between the right-handed and left-handed neutrinos of each flavor. Models of gauged B − L such as these that sit below the TeV scale are possible with, for example, SOð10Þ embedding of B − L [6], or leptogenesis scenarios [7], and the motivation for a comprehensive search for HNLs down to the ∼MeV mass scale is clear [8][9][10]. In this work, we take a relatively model agnostic set of parameters to search for HNLs in the MeV-GeV mass range, with the relevant physical phenomena described in terms of g B−L , U α , m Z 0 , and m N . ...
New gauge bosons coupled to heavy neutral leptons (HNLs) are simple and well-motivated extensions of the Standard Model. In searches for HNLs in proton fixed-target experiments, we find that a large population of gauge bosons ( Z ′ ) produced by proton bremsstrahlung may decay to HNLs, leading to a significant improvement in existing bounds on the ( m HNL , U α ), where U α represent the mixing between HNL and the active neutrinos with flavor α . We study this possibility in fixed target experiments with the 8 GeV proton beams, including SBND, MicroBooNE, and ICARUS, as well as DUNE and DarkQuest at 120 GeV. We find the projected sensitivities to additional Z ′ -mediated HNL production can bring the seesaw mechanism of the neutrino masses within a broadened experimental reach.
Published by the American Physical Society 2025
... This phenomenon, known as neutrino flavour oscillation, links flavour states (ν e , ν µ , ν τ ), which determine their weak interactions, with mass states (ν 1 , ν 2 , ν 3 ), which are crucial for understanding the dynamics of the Universe. Interestingly, a hypothetical fourth neutrino state (ν 4 ), with a well-defined mass m 4 , could exist as a natural extension of the Standard Model of particle physics [2]. This mass state would predominantly lack a significant flavour component, with small contributions from e, µ, and τ flavours. ...
... The experiment observed a neutrino energy distribution consistent with oscillations driven by sterile neutrinos, characterized by m 4 ≃ 2.70 ± 0.22 eV and sin 2 (2θ ee ) = 0.36 ± 0.12. However, these results remain contentious, as no scientific consensus has been reached [2]. ...
... Despite variations in neutrino flavour, energy, and baseline, these anomalies collectively hint at the possibility of non-standard neutrino oscillations involving sterile neutrinos associated with a mass range of 0.1 eV to several tens of eV [2]. However, their statistical significance, ranging from two to four standard deviations, offers only weak evidence. ...
Neutrinos are the most abundant fundamental matter particles in the Universe and play a crucial role in particle physics and cosmology. Neutrino oscillation, discovered about 25 years ago, reveals that the three known species mix with each other. Anomalous results from reactor and radioactive-source experiments suggest a possible fourth neutrino state, the sterile neutrino, which does not interact via the weak force. The KATRIN experiment, primarily designed to measure the neutrino mass via tritium -decay, also searches for sterile neutrinos suggested by these anomalies. A sterile-neutrino signal would appear as a distortion in the -decay energy spectrum, characterized by a discontinuity in curvature (kink) related to the sterile-neutrino mass. This signature, which depends only on the shape of the spectrum rather than its absolute normalization, offers a robust, complementary approach to reactor experiments. KATRIN examined the energy spectrum of 36 million tritium -decay electrons recorded in 259 measurement days within the last 40 electronvolt below the endpoint. The results exclude a substantial part of the parameter space suggested by the gallium anomaly and challenge the Neutrino-4 claim. Together with other neutrino-disappearance experiments, KATRIN probes sterile-to-active mass splittings from a fraction of an electron-volt squared to several hundred electron-volts squared, excluding light sterile neutrinos with mixing angles above a few percent.
... In the face of significant theoretical uncertainty regarding the masses of sterile neutrinos, a wide range of varying experimental and theoretical probes have been brought to bear on the existence of sterile neutrinos over many orders of magnitude in mass (e.g., [4][5][6][7][8][9]). Such searches include colliders, beta decays, accelerators, as well as astrophysical and cosmological signatures. ...
Sterile neutrinos can be produced through mixing with active neutrinos in the hot, dense core of a core-collapse supernova (SN). The standard bounds on the active-sterile mixing (sin² θ) from SN arise from SN1987A energy-loss, requiring E loss < 10⁵² erg. In this work, we discuss a novel bound on sterile neutrino parameter space arising from the energy deposition through its decays inside the SN envelope. Using the observed underluminous SN IIP population, this energy deposition is constrained to be below ∼ 10⁵⁰ erg. Focusing on sterile neutrino mixing only with tau neutrino, for heavy sterile masses ms in the range 100 – 500 MeV, we find stringent constraints on sin² θτ reaching two orders of magnitude lower than those from the SN1987A energy loss argument, thereby probing the mixing angles required for Type-I seesaw mechanism. Similar bounds will also be applicable to sterile mixing only with muons (sin² θμ ).
... Then, we need to implement non-unitarity into the (3 + 1) model. We note that the problem of sterile neutrinos [54] or non-unitarity [53] is widely discussed in the community as possible candidates for physics beyond the νSM. But, in our setting we need the both, "sterile neutrino and non-unitarity". ...
An excess observed in the accelerator neutrino experiments in the channel at high confidence level (CL) has been interpreted as due to eV-scale sterile neutrino(s). But, it has been suffered from the problem of ``appearance - disappearance tension'' at the similarly high CL because the measurements of the channel do not observe the expected event number depletion corresponding to the sterile contribution in the appearance channel. We suggest non-unitarity as a simple and natural way of resolving the tension, which leads us to construct the non-unitary (3+1) model. With reasonable estimation of the parameters governing non-unitarity, we perform an illustrative analysis to know if the tension is resolved in this model. At the best fit of the appearance signature we have found the unique solution with , which is consistent with the (reactors + Ga) data combined fit. Unexpectedly, our tension-easing mechanism bridges between the two high CL signatures, the BEST and LSND-MiniBooNE anomalies.
... It couples to Standard Model particles in the same manner as active neutrinos but with a coupling suppressed by a small mixing parameter θ(≪ 1). In the broken phase of electroweak symmetry, the mass term is given by (see [20][21][22][23][24] for the review of the model) ...
Recently, a high-energy neutrino event, designated KM3-230213A, was observed by the KM3NeT/ARCA detector in the Mediterranean Sea. This event is characterized by a reconstructed muon energy of approximately 120 PeV, corresponding to a median neutrino energy of roughly 220 PeV. To understand the origin, it is essential to investigate consistency with multi-messenger observations--particularly gamma-ray constraints--in various theoretical scenarios within and beyond the Standard Model. Motivated by this, we explore the possibility that the detected event does not originate from conventional neutrinos but rather from right-handed neutrinos (sterile neutrinos) mixing with active neutrinos, leading to the observed muon signal. Such cosmic-ray dark radiation may have originated either in the early Universe or through dark matter decay in the present epoch. We show that in both cases, while satisfying existing general constraints on light sterile neutrinos, the stringent multi-messenger gamma-ray limits can be significantly alleviated. A distinct prediction of this scenario is that such events can arrive from directions through Earth that would typically attenuate conventional neutrinos. A related scenario involving cosmic-ray boosted WIMP dark matter is also discussed.
... In particular, the two-body decay of dark matter particles into photon-emitting final states is a promising avenue for indirect detection (e.g., [2][3][4][5][6][7][8][9][10][11][12]), as it yields a spectral line whose characteristics can be directly linked to the underlying particle properties. Indeed, indirect detection is one of the most powerful tools for probing particle models such as sterile neutrinos, axion-like particles (ALPs), or light moduli (see reviews, e.g., [13][14][15][16][17] for sterile neutrinos, and ALPs [18][19][20][21][22][23][24][25], as well as [26] for generic dark matter). 1 Spectrographs with a resolving power of ...
We investigate the indirect detection search of the two-body decay of dark matter particles into final states containing a photon, a process predicted in various promising dark matter models such as axion-like particles and sterile neutrinos. Recent and near-future photon detectors with a resolution are primarily optimized for the velocity dispersion of dark matter in the Milky Way. When performing indirect detection of dark matter in objects other than the Milky Way, one should take into account the contribution from Milky Way dark matter. As a result, the dark matter signal observed by a detector is predicted to exhibit a two-peak structure in many targets, owing to the Doppler shift, differences in radial velocities and the good energy resolution. An analysis incorporating this two-peak effect was performed using the latest XRISM observation data of the Centaurus galaxy cluster~\cite{XRISM:2025axf}. Although, due to the relatively short observation time, our derived limit is weaker than some existing limits, among dark matter searches in galaxy clusters our limit is one of the most stringent (at least in certain mass ranges). We also perform the usual single-peak analysis, for considering the various scenarios, that prefer narrow-line photon from the faraway galaxy cluster. Future data releases from XRISM as well as other observatories will further strengthen our conclusions.
