Sun heated MeV-scale dark matter and the XENON1T electron recoil excess

The XENON1T collaboration reported an excess of the low-energy electron recoil events between 1 and 7 keV. We explore the possibility to explain such an anomaly by the MeV-scale dark matter (DM) heated by the interior of the Sun due to the same DM-electron interaction as in the detector. The kinetic energies of heated DM particles can reach a few keV, and can potentially account for the excess signals detected by XENON1T. We study different form factors of the DM-electron interactions, F(q) proportional to q(i) with q being the momentum exchange and i = 0, 1, 2, and find that for all these cases the inclusion of the Sun-heated DM component improves the fit to the XENON1T data. The inferred DM-electron scattering cross section (at q = alpha m(e) where alpha is the fine structure constant and m(e) is electron mass) is from similar to 10(-38) cm(2) (for i = 0) to similar to 10(-42) cm(2) (for i = 2). We also derive constraints on the DM-electron cross sections for these form factors, which are stronger than previous results with similar assumptions. We emphasize that the Sun-heated DM scenario relies on the minimum assumption on DM models, which serves as a general explanation of the XENON1T anomaly via DM-electron interaction. The spectrum of the Sun-heated DM is typically soft comparing to other boosted DM, so the small recoil events are expected to be abundant in this scenario. More sensitive direct detection experiments with lower thresholds can possibly distinguish this scenario with other boosted DM models or solar axion models.

Automated summary

The XENON1T collaboration reported an excess of low-energy electron recoil events and explored the possibility of explaining it with MeV-scale dark matter heated by the Sun. Different form factors of DM-electron interactions were studied and the inclusion of Sun-heated DM improved the fit to the data. Inferred DM-electron scattering cross sections were obtained and constraints for these form factors were derived, showing stronger results than previous studies.