Explaining the XENON1T Excess with Luminous Dark Matter

Oscillations of Active Neutrinos at Short Baseline in the Model with Three Decaying Sterile Neutrinos

To study the oscillations of active neutrinos in the framework of the model with three active and three sterile neutrinos, the analytical expressions are obtained for the appearance and survival probabilities of different neutrino flavors taking into account the decaying sterile neutrinos contributions. In the framework of the considered phenomenological neutrino model, we make an interpretation of the experimentally detected XENON1T-excess of electronic recoil events in the energy range of 1–7 keV as a result of the radiative decay of a sterile neutrino with a mass of about 7 keV. Estimations of the decay parameters for the radiative decay of Majorana sterile neutrinos due to the magnetic dipole transitions into the active neutrino states are made. The value of the parameter of active and sterile neutrinos mixing has been derived from the Baksan Experiment on Sterile Transitions (BEST) experimental data. The graphical dependences for the probabilities of appearance and survival of muonic and electron neutrinos at short baseline (SBL) are presented with the use of that gained from the experimental data estimations of the model parameters.

Shedding new light on sterile neutrinos from XENON1T experiment

The XENON1T collaboration recently reported the excess of events from recoil electrons, possibly giving an insight into new area beyond the Standard Model (SM) of particle physics. We try to explain this excess by considering effective interactions between the sterile neutrinos and the SM particles. In this paper, we present an effective model based on one-particle-irreducible interaction vertices at low energies that are induced from the SM gauge symmetric four-fermion operators at high energies. The effective interaction strength is constrained by the SM precision measurements, astrophysical and cosmological observations. We introduce a novel effective electromagnetic interaction between sterile neutrinos and SM neutrinos, which can successfully explain the XENON1T event rate through inelastic scattering of the sterile neutrino dark matter from Xenon electrons. We find that sterile neutrinos with masses around 90 keV and specific effective coupling can fit well with the XENON1T data where the best fit points preserving DM constraints and possibly describe the anomalies in other experiments.

Hydrogen Portal to Exotic Radioactivity

We show that in a special class of dark sector models, the hydrogen atom can serve as a portal to new physics, through its decay occurring in abundant populations in the Sun and on Earth. The large fluxes of hydrogen decay daughter states can be detected via their decay or scattering. By constructing two models for either detection channel, we show that the recently reported excess in electron recoils at xenon1t could be explained by such signals in large regions of parameter space unconstrained by proton and hydrogen decay limits.

XENON1T Excess from Anomaly-Free Axionlike Dark Matter and Its Implications for Stellar Cooling Anomaly

Recently, an anomalous excess was found in the electronic recoil data collected at the XENON1T experiment. The excess may be explained by an axionlike particle (ALP) with a mass of a few keV and a coupling to electron of g_{ae}∼10^{-13}, if the ALP constitutes all or some fraction of local dark matter (DM). In order to satisfy the x-ray constraint, the ALP coupling to photons must be significantly suppressed compared to that to electrons. This strongly suggests that the ALP has no anomalous couplings to photons; i.e., there is no U(1)_{PQ}-U(1)_{em}-U(1)_{em} anomaly. We show that such anomaly-free ALP DM predicts an x-ray line signal with a definite strength through the operator arising from threshold corrections, and compare it with the projected sensitivity of the ATHENA x-ray observatory. The abundance of ALP DM can be explained by the misalignment mechanism, or by thermal production if it constitutes a part of DM. In particular, we find that the anomalous excess reported by the XENON1T experiment as well as the stellar cooling anomalies from white dwarfs and red giants can be explained simultaneously better when the ALP constitutes about 10% of DM. As concrete models, we revisit the leptophilic anomaly-free ALP DM considered in K. Nakayama, F. Takahashi, and T. T. Yanagida [Phys. Lett. B 734, 178 (2014)] as well as an ALP model based on a two Higgs doublet model in the Supplemental Material.

Electric But Not Eclectic: Thermal Relic Dark Matter for the XENON1T Excess

The identity of dark matter is being sought with increasingly sensitive and voluminous underground detectors. Recently the XENON1T Collaboration reported excess electronic recoil events, with most of these having recoil energies around 1-30 keV. We show that a straightforward model of inelastic dark matter produced via early Universe thermal freeze-out annihilation can account for the XENON1T excess. Remarkably, this dark matter model consists of a few simple elements: sub-GeV mass Dirac fermion dark matter coupled to a lighter dark photon kinetically mixed with the standard model photon. A scalar field charged under the dark U(1) gauge symmetry can provide a mass for the dark photon and splits the Dirac fermion component state masses by a few keV, which survive in equal abundance and interact inelastically with electrons and nuclei.

Boosted Dark Matter Interpretation of the XENON1T Excess

We propose boosted dark matter (BDM) as a possible explanation for the excess of keV electron recoil events observed by XENON1T. BDM particles have velocities much larger than those typical of virialized dark matter, and, as such, BDM-electron scattering can naturally produce keV electron recoils. We show that the required BDM-electron scattering cross sections can be easily realized in a simple model with a heavy vector mediator. Though these cross sections are too large for BDM to escape from the Sun, the BDM flux can originate from the Galactic Center or from halo dark matter annihilations. Furthermore, a daily modulation of the BDM signal will be present, which could not only be used to differentiate it from various backgrounds but would also provide important directional information for the BDM flux.

Neutrino Self-Interactions and XENON1T Electron Recoil Excess

The XENON1T collaboration recently reported an excess in electron recoil events in the energy range between 1-7 keV. This excess could be understood to originate from the known solar neutrino flux if neutrinos couple to a light vector mediator with strength g_{νN} that kinetically mixes with the photon with strength χ and g_{νN}χ∼10^{-13}. Here, we show that such coupling values can naturally arise in a renormalizable model of long-range vector-mediated neutrino self-interactions. The model could be distinguished from other explanations of the XENON1T excess by the characteristic 1/T^{2} energy dependence of the neutrino-electron scattering cross section. Other signatures include invisible Higgs and Z decays and leptophilic charged Higgses at a few 100 GeV. ALPS II will probe part of the viable parameter space.