MeV Scale Research Articles

Lμ−Lτ solution to the IceCube ultrahigh-energy neutrino deficit in light of NA64

In this work we analyze the scenario where a MeV scale Lμ−Lτ gauge boson can explain the deficit in the diffuse ultrahigh-energy (UHE) astrophysical neutrino spectrum observed in IceCube, as well as the discrepancy between experimental and e+e− scattering data-driven Standard Model 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 1011 muons on target NA64-μ will completely probe this region. Published by the American Physical Society 2024

First demonstration of a combined light and charge pixel readout on the anode plane of a LArTPC

The novel SoLAr concept aims to extend sensitivities of liquid-argon neutrino detectors down to the MeV scale for next-generation detectors. SoLAr plans to accomplish this with a liquid-argon time projection chamber that employs an anode plane with dual charge and light readout, which enables precision matching of light and charge signals for data acquisition and reconstruction purposes. We present the results of a first demonstration of the SoLAr detector concept with a small-scale prototype detector integrating a pixel-based charge readout and silicon photomultipliers on a shared printed circuit board. We discuss the design of the prototype, and its operation and performance, highlighting the capability of such a detector design.

How viable is a QCD axion near 10 MeV?

There has been an attempt to revive the visible QCD axion at the 10 MeV scale assuming that it exclusively couples to the first-generation quarks and the electron. This variant of the QCD axion is claimed to remain phenomenologically viable, partly due to a clever model construction that induces tree-level pion-phobia and exploits uncertainties inherent in the chiral perturbation theory. We confront this model with the cosmological domain wall problem, the quality issue and constraints arising from the electron electric dipole moment. It is also pointed out that the gluon loop-generated axion-top coupling can provide a very large contribution to rare B-meson decays, such that the present LHCb data for B0 → K*0e+e− rule out the model for the axion mass larger than 30 MeV. There is a strong motivation for pushing the experimental analysis of B → K(*)e+e− to a lower e+e− invariant mass window, which will conclusively determine the fate of the model, as its contribution to this branching ratio significantly exceeds the Standard Model prediction.

The Ziré instrument onboard the NUSES space mission

The Ziré experiment is an instrument on board the NUSES (NeUtrino and Seismic Electromagnetic Signals) satellite dedicated to test new techniques for the study of low energy cosmic radiation, Sun–Earth environment, space weather and magnetosphere–ionosphere–lithosphere coupling (MILC). Ziré will consist of a fiber tracker, a stack of plastic scintillators, an array of LYSO crystals and an anticoincidence system. A dedicated Low Energy Module (LEM) will extend the sensitive energy range down to the MeV scale for charged particles. In this work, a general overview of the Ziré payload will be given, together with a focus on the design and the review of dedicated tests on the first prototype.

Theoretical point of view on Cabibbo angle anomaly

In this paper, we present the current situation of the determinations of the first-row CKM components and show the Cabibbo angle anomaly corresponding to a deficit in the first-row CKM unitarity condition at the [Formula: see text] level. In this contribution, we show two new physics interpretations: heavy vector-like quark models and a MeV scale sterile neutrino scenario. The super tau-charm facility will directly probe the other CKM unitarity conditions related to [Formula: see text].

Characterization of Transition Edge Sensors for Decay Energy Spectrometry

By using a superconducting transition edge sensor (TES) to measure the thermal energy of individual decay events with high energy resolution, decay energy spectrometry provides a unique fingerprint to identify each radionuclide in a sample. The proposed measurement requires optimizing the thermal parameters of the detector for use with 5 MeV scale energy deposited by alpha decay of the sample radionuclides. The thermal performance of deep-etched silicon TES chips is examined with the use of an onboard resistive heater. With known heater power and bath temperature, the thermal conductance, heat capacity, and frame temperature are calculated and compared to theory.

Imprints of light dark matter on the evolution of cosmic neutrinos

Neutrinos are often considered as a portal to new physics beyond the Standard Model (SM) and might possess phenomenologically interesting interactions with dark matter (DM). This paper examines the cosmological imprints of DM that interacts with and is produced from SM neutrinos at temperatures below the MeV scale. We take a model-independent approach to compute the evolution of DM in this framework and present analytic results which agree well with numerical ones. Both freeze-in and freeze-out regimes are included in our analysis. Furthermore, we demonstrate that the thermal evolution of neutrinos might be substantially affected by their interaction with DM. We highlight two distinctive imprints of such DM on neutrinos: (i) a large, negative contribution to N eff, which is close to the current experimental limits and will readily be probed by future experiments; (ii) spectral distortion of the cosmic neutrino background (CνB) due to DM annihilating into neutrinos, a potentially important effect for the ongoing experimental efforts to detect CνB.

A cosmic window on the dark axion portal

Axions and dark photons are common in many extensions of the Standard Model. The dark axion portal — an axion coupling to the dark photon and photon — can significantly modify their phenomenology. We study the cosmological constraints on the dark axion portal from Cosmic Microwave Background (CMB) bounds on the energy density of dark radiation, ∆Neff. By computing the axion-photon-dark photon collision terms and solving the Boltzmann equations including their effects, we find that light axions are generally more constrained by ∆Neff than from supernova cooling or collider experiments. However, with dark photons at the MeV scale, a window of parameter space is opened up above the supernova limits and below the experimental exclusion, allowing for axion decay constants as low as fa ~ 104 GeV. This region also modifies indirectly the neutrino energy density, thus relaxing the cosmological upper bound on the sum of neutrino masses. Future CMB measurements could detect a signal or close this open window on the dark axion portal.

Constraints on new physics around the MeV scale with cosmological observations

Constraints on new physics around the MeV scale with cosmological observations

Automatic, high-order, and adaptive algorithms for Brillouin zone integration

We present efficient methods for Brillouin zone integration with a non-zero but possibly very small broadening factor \etaη, focusing on cases in which downfolded Hamiltonians can be evaluated efficiently using Wannier interpolation. We describe robust, high-order accurate algorithms automating convergence to a user-specified error tolerance \varepsilonε, emphasizing an efficient computational scaling with respect to \etaη. After analyzing the standard equispaced integration method, applicable in the case of large broadening, we describe a simple iterated adaptive integration algorithm effective in the small \etaη regime. Its computational cost scales as \mathcal{O}(\log^3(\eta^{-1}))𝒪(log3(η−1)) as \eta \to 0^+η→0+ in three dimensions, as opposed to \mathcal{O}(\eta^{-3})𝒪(η−3) for equispaced integration. We argue that, by contrast, tree-based adaptive integration methods scale only as \mathcal{O}(\log(\eta^{-1})/\eta^{2})𝒪(log(η−1)/η2) for typical Brillouin zone integrals. In addition to its favorable scaling, the iterated adaptive algorithm is straightforward to implement, particularly for integration on the irreducible Brillouin zone, for which it avoids the tetrahedral meshes required for tree-based schemes. We illustrate the algorithms by calculating the spectral function of SrVO_33 with broadening on the meV scale.

Analysis of the Radiation Field Generated by 200-MeV Electrons on a Target at the CLEAR Accelerator at CERN

The radiation showers generated by the interaction of high-energy electrons with matter include neutrons with an energy distribution peaked at the MeV scale, produced via photonuclear reactions, allowing measurements of neutron-induced Single-Event Effects in electronic devices. In this work we study a setup where the 200-MeV electron beam of the CLEAR accelerator at CERN is directed on an aluminum target to produce a radiation field with a large neutron component. The resulting environment is analyzed by measuring the Single-Event Upset (SEU) and Latchup rates in well-characterized SRAMs, as well as the Total Ionizing Dose in passive Radio-Photo-Luminescence dosimeters, and by comparing the results with predictions from FLUKA simulations. We find that a lateral shielding made of lead protects the SRAMs from an excessive TID rate, yielding an optimal configuration for SEU measurements, particularly in SRAMs that are highly sensitive to MeV-scale neutrons. This setup provides an interesting complementary neutron source with respect to standard neutron facilities based on spallation targets or radioactive sources.

Dark matter and [formula omitted] in ISS(2,3) based Gauged [formula omitted] symmetric model

We proposed a model which can explain the neutrino phenomenology, dark matter and anomalous magnetic moment (g−2) in a common framework. The inverted seasaw (ISS)(2,3) mechanism has been incorporated, in which we get an extra sterile state and this state act as a viable dark matter candidate. The right handed neutrino mass is obtained in TeV scale, which is accessible at LHC. The anomaly free U(1)Le−Lμ gauge symmetry is introduced to explain the anomalous magnetic moment of electron and muon because it provides a natural origin of (g−2) in a very minimal setup. The corresponding MeV scale gauge boson successfully explain the anomalous magnetic moment of electron and muon (g−2)e,μ, simultaneously. Thus obtained neutrino phenomenology and relic abundance of dark matter are compatible with experimental results.

Directional direct detection of light dark matter up-scattered by cosmic rays from direction of the Galactic center

Dark matter with MeV scale mass is difficult to detect with standard direct search detectors. However, they can be searched for by considering the up-scattering of kinetic energies by cosmic rays. Because the dark matter density is higher in the central region of the Galaxy, the up-scattered dark matter will arrive at Earth from the direction of the Galactic center. Once the dark matter is detected, we can expect to recognize this feature by directional direct detection experiments. In this study, we simulate the nuclear recoils of the up-scattered dark matter and quantitatively reveal that a large amount of this type of dark matter is arriving from the direction of the Galactic center. Also, we have shown that the characteristic signatures of the up-scattered dark matter can be verified with more than 5σ confidence levels for the assumed target atoms and future upgrades to directional detectors.

MeV dark matter with MeV dark photons in Abelian kinetic mixing theories

We consider the cosmology and phenomenology of a dark photon portal to a simple dark sector consisting of a single, light, fermionic dark matter particle species with mass in the MeV range. We entertain three possible kinetic mixing structures of a new Abelian gauge group U(1)dark with the visible sector through U(1)e.m., U(1)Y and T[SU(2)_L]. We assume the dark photon to be massive and around the MeV scale, thus close to the mass scale of the dark matter candidate. We compute the dark matter relic density via freeze-out and freeze-in, entertaining the additional possibility of a late inflationary period that could dilute the dark matter yield of heavy candidates, and (ii) additional production modes, for models with under-abundant thermal production. We explore the parameter space compatible with a variety of experimental and astrophysical bounds, and discuss prospects for discovery with new CMB probes and MeV gamma-ray telescopes.

Dark matter substructures affect dark matter-electron scattering in xenon-based direct detection experiments

Recent sky surveys have discovered a large number of stellar substructures. It is highly likely that there are dark matter (DM) counterparts to these stellar substructures. We examine the implications of DM substructures for electron recoil (ER) direct detection (DD) rates in dual phase xenon experiments. We have utilized the results of the LAMOST survey and considered a few benchmark substructures in our analysis. Assuming that these substructures constitute 10% of the local DM density, we study the discovery limits of DM-electron scattering cross sections considering one kg-year exposure and 1, 2, and 3 electron thresholds. With this exposure and threshold, it is possible to observe the effect of the considered DM substructure for the currently allowed parameter space. We also explore the sensitivity of these experiments in resolving the DM substructure fraction. For all the considered cases, we observe that DM having mass mathcal{O}(10) MeV has a better prospect in resolving substructure fraction as compared to mathcal{O}(100) MeV scale DM. We also find that within the currently allowed DM-electron scattering cross-section; these experiments can resolve the substructure fraction (provided it has a non-negligible contribution to the local DM density) with good accuracy for mathcal{O}(10) MeV DM mass with one electron threshold.

Investigating the collinear splitting effects of boosted dark matter at neutrino detectors

We study the probing prospects of cosmic ray boosted dark matter (DM) in the framework of simplified electron-philic dark photon model. Focusing on the dark matter and dark photon masses around keV ~ MeV scale, we consider the bounds obtained from the XENON1T and Super-K experiments. The electron bound state effects are treated carefully in calculating the XENON1T constraint. As for the detection at neutrino detector where the energy threshold is relatively higher, the large logarithmic effects induced by the scale hierarchy between the masses and momentum transfer are considered by introducing the DM parton distribution function (PDF). The logarithmic effects will reduce the electron recoil rate for DM scattering in neutrino detectors. Moreover, we find the DUNE and JUNO experiments provide high sensitivities for probing the dark photon component in the DM PDF through the dark Compton process. We also check the Bullet Cluster constraint on the DM self-scattering cross section.

Sterile neutrinos in light of the Cabibbo-angle anomaly

Based on recent developments in the lattice simulations and calculations of the radiative corrections to the charged-current interactions, the uncertainties for each component in the CKM matrix have been sophisticated. It is known that the first-row CKM unitarity is violated at about 3σ level, implying a 3σ level deviation from the standard model prediction. This new deviation is called Cabibbo-Angle Anomaly (CAA). These CKM components are mainly extracted from kaon, pion, and the superallowed beta decays. In this contribution, we point out that a MeV scale sterile neutrino can economically explain the CAA. We consistently investigate the sterile neutrino contributions to the kaon, pion, superallowed beta decays, and also the Fermi coupling constant.

Thermal Leptophilic Light Vector Dark Matter with Spinor Mediator and Muon (g-2) Anomaly

Inspired by the recently new measurement of (g − 2)μ at FermiLab and reported upper bound for electron-dark matter (DM) recoil by the XENON1T collaboration, we revisited phenomenology of a light MeV scale vector dark matter in a leptophilic extension of standard model while a new spinor field plays the role of mediator. A viable parameter space is considered to discuss the possibility of light dark matter relic density as well as anomalous magnetic moment of the muon. We study DM-electron direct detection and cosmological bounds on the parameters space of the model. It is shown that although new bound of (g − 2)μ anomaly greatly confines the parametric space of the model, the thermal light dark matter can exist for \(\mathrm {M_{DM}} \sim 10^{-1}-10^{1} \text {GeV}\).

Synergetic effects of combining TM single- and double-atom catalysts embedded in C2N on inducing half-metallicity: DFT study

Designing 2D-materials that exhibit half-metallic properties is crucially important in spintronic devices that are used in low-power high-density logic circuits. The large pores in the C2N morphology can stably accommodate various configurations of transition-metal (TM) atoms that can lead to ferromagnetic (FMC) and anti-ferromagnetic coupling interactions among them, and thus paving the way for achieving half-metallic characteristics. In the present study, we use manganese ‘Mn’ as a promising catalyst and the spin-polarized density-functional theory to search for suitable configurations of metal atoms that yield half-metallicity. Test samples comprised of single-atom catalyst (SAC) and double-atom catalyst (DAC) of Mn embedded in a C2N sample of size 2 × 2 primitive cells as well as their combinations in neighboring large pores (i.e. SAC–SAC, SAC–DAC, and DAC–DAC). Tests were extended to screen many other TM catalysts and the results showed the existence of half metallicity in just five cases: (a) C2N:Mn (DAC, SAC–SAC, and SAC–DAC); (b) C2N:Fe (DAC); and (c) C2N:Ni (SAC–DAC). Our results further showed the origins of half-metallicity to be attributed to FMC interactions between the catalysts with the six mirror images, formed by the periodic-boundary conditions. The FMC interaction is found to have strength of about 20 meV and critical length scale up to about ∼21–29 Å, dependent on both the type of magnetic impurity and the synergetic effects. The potential relevance of half-metallicity to spintronic device application is discussed. Our theoretical results have been benchmarked to the available data in literature and they were found to be in good agreements.

Self-interacting freeze-in dark matter in a singlet doublet scenario

We examine the non-thermal production of dark matter in a scalar extended singlet doublet fermion model where the lightest admixture of the fermions constitutes a suitable dark matter candidate. The dark sector is non-minimal with the MeV scale singlet scalar, which is stable in the Universe lifetime and can mediate the self-interaction for the multi-GeV fermion dark matter mitigating the small scale structure anomalies of the Universe. If the dark sector is strongly coupled to yield a velocity dependent large self-interaction cross section, it undergoes internal dark thermal equilibrium after freeze-in production. We essentially end up with suppressed relic abundance for the fermion dark matter in a traditional radiation dominated Universe. In contrast, the presence of a modified cosmological phase in the early era drives the fermion dark matter to satisfy nearly the whole amount of observed relic. It also turns out that the assumption of an unconventional cosmological history can allow the GeV scale dark matter to be probed at LHC from displaced vertex signature with improved sensitivity.