The electron capture decay of the isotope 163-Ho has been proposed since a long time as a candidate for measuring the electron neutrino mass and recently the interest on this idea has been renewed. In this paper we note that a direct observation of the cosmic antineutrino background could be made using a target made of this isotope. We further discuss the requests for an experiment aiming to obtain this result.
$^{163}$Ho has been considered as a suitable candidate for the capture of relic antineutrinos. However, the detection of the relic antineutrino using $^{163}$Ho is extremely challenging with current techniques. Therefore, we have searched for new targets for relic antineutrino detections through the resonant capture on nuclides undergoing electron capture. We have investigated nuclear and atomic properties of all nuclides. And we finally propose $^{131}$Ba, $^{159}$Dy, $^{175}$Hf, $^{195}$Au, and $^{243}$Cm as new candidates for the relic antineutrino detection, and call for high precise exper…
The mechanism of beta decay in nature is not understood yet. Mirrored energy spectra of electron and antineutrino can clarify the situation. A special experiment is needed to measure antineutrino spectrum from known beta-decaying isotope to compare it with the beta one. One of ongoing experiments with large volume detector can be chosen to make the experiment. Another possibility is to make a special experiment close to a powerful source of mixture of known beta-decaying isotopes. If sufficient differences in shape will be observed the method of antineutrino spectrum calculation should be revi…
The time evolution of a neutrino is dependent on its initial properties at creation including flavor, energy, and wavepacket size. There exists no solid theoretical prediction for the latter property in the context of nuclear beta decay, despite the importance of this process for the past, present, and future of neutrino experimentation. In this paper, we provide a quantitative prediction for the size of a beta-decay-induced electron antineutrino wavepacket by treating the parent nucleus decaying to an entangled antineutrino-recoil system using the formalism of open quantum systems. Of central…
Solar neutrino experiments are highly sensitive to sources of $ν\to\overlineν$ conversions in the $^8$B neutrino flux. In this work we adapt these searches to non-minimal sterile neutrino models recently proposed to explain the LSND, MiniBooNE, and reactor anomalies. The production of such sterile neutrinos in the Sun, followed the decay chain $ν_4 \to νϕ\to νν\overlineν$ with a new scalar $ϕ$ results in upper limits for the neutrino mixing $|U_{e4}|^2$ at the per mille level. We conclude that a simultaneous explanations of all anomalies is in tension with KamLAND, Super-Kamiokande, and Borexi…
Improved Big Bang Nucleosynthesis constraints on decaying massive relics
Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；Dipartimento di Fisica, Sapienza Università di Roma & Sezione INFN Roma1（罗马第一大学物理系与INFN罗马一分部）；Service de Physique Théorique, Université Libre de Bruxelles（布鲁塞尔自由大学理论物理服务处）；CP3-Origins, University of Southern Denmark（南丹麦大学CP3起源中心）
A massive particle decaying into neutrinos in the early Universe is known to be less constrained than if it was decaying into other standard model particles. However, even if the decay proceeds into neutrinos, the latter still inevitably emit secondary particles undergoing electromagnetic interactions that can be probed. We analyse in details how sensitive various cosmological probes are to such secondary particles, namely CMB anisotropies, CMB spectral distortions, and Big Bang Nucleosynthesis. For relics whose lifetime is shorter than the age of the Universe, this leads to original and strin…
Relic neutrinos from the early universe are predicted to have a relatively large number density, but extremely low energies. Hence, the only possible interaction proceeds via neutrino capture on beta-decaying nuclei. In case relic neutrinos are captured by beta-decaying nuclei in the Sun, the neutrinos normally emerging from the decay of these nuclei will be missing from the overall number of solar neutrinos registered in neutrino experiments. Within the Sun, ${}^8\mathrm{B}$ and three nuclei from the CNO cycle are found to be suitable for this kind of process. Their cross section as well as t…
We show how 21 cm cosmology can test relic neutrino radiative decays into sterile neutrinos. Using recent EDGES results, we derive constraints on the lifetime of the decaying neutrinos. If the EDGES anomaly will be confirmed, then there are two solutions, one for much longer and one for much shorter lifetimes than the age of the universe, showing how relic neutrino radiative decays can explain the anomaly in a simple way. We also show how to combine EDGES results with those from radio background observations, showing that potentially the ARCADE 2 excess can be also reproduced together with the…
The long standing anomaly in the positron flux as measured by the PAMELA and AMS-02 experiments could potentially be explained by dark matter (DM) annihilations. This scenario typically requires a large "boost factor" to be consistent with a thermal relic dark matter candidate produced via freeze-out. However, such an explanation is disfavored by constraints from CMB observations on energy deposition during the epoch of recombination. We discuss a scenario called late-decaying two-component dark matter (LD2DM), where the entire DM consists of two semi-degenerate species. Within this framework,…
We consider long-lived relic particles as the source of the PeV-scale neutrinos detected at the IceCube observatory over the last six years. We derive the present day neutrino flux, including primary neutrinos from direct decays, secondary neutrinos from electroweak showering, and tertiary neutrinos from re-scatters off the relic neutrino background. We compare the high-energy neutrino flux prediction to the most recently available datasets and find qualitative differences to expected spectra from other astrophysical processes. We utilize electroweak corrections to constrain heavy decaying rel…
Neutrino capture on beta-decaying nuclei is currently the only known potentially viable method of detection of cosmic background neutrinos. It is based on the idea of separation of the spectra of electrons or positrons produced in captures of relic neutrinos on unstable nuclei from those from the usual $β$-decay and requires very high energy resolution of the detector, comparable to the neutrino mass. In this paper we suggest an alternative method of discrimination between neutrino capture and $β$-decay, based on periodic variations of angular correlations in inverse beta decay transitions ind…
We consider models of decaying spin-1 dark matter whose dominant coupling to the standard model sector is through a dark-Higgs Yukawa portal connecting a TeV-scale vector-like lepton to the standard model (right-handed) electron. Below the electron-positron threshold, dark matter has very slow, loop-suppressed decays to photons and (electron) neutrinos, and is stable on cosmological time-scale for sufficiently small gauge coupling values. Its relic abundance is set by in-equilibrium dark lepton decays, through the freeze-in mechanism. We show that this model accommodates the observed dark matt…
We study effects of long-lived massive particles, which decay during the big-bang nucleosynthesis (BBN) epoch, on the primordial abundances of light elements. Compared to the previous studies, (i) the reaction rates of the standard BBN reactions are updated, (ii) the most recent observational data of light element abundances and cosmological parameters are used, (iii) the effects of the interconversion of energetic nucleons at the time of inelastic scatterings with background nuclei are considered, and (iv) the effects of the hadronic shower induced by energetic high energy anti-nucleons are i…
The latest Lyman-$α$ forest data severely constrain the conventional warm dark matter solution to small-scale issues in the cold dark matter paradigm. It has been also reported that unconstrained astrophysical processes may address the issues. In response to this situation, we revisit the decaying dark matter solution to the issues, discussing possible signatures to discriminate decaying dark matter from astrophysical processes as a solution to small-scale issues. We consider an axinolike particle (ALPino) decaying into an axionlike particle (ALP) and gravitino with the lifetime around the age…
