Sun Heated MeV-scale Dark Matter and the XENON1T Electron Recoil Excess

TL;DR

This paper proposes that MeV-scale dark matter particles heated by the Sun could explain the XENON1T electron recoil excess, providing a minimal and general DM-electron interaction scenario that fits the data and constrains cross sections.

Contribution

It introduces a novel Sun-heated dark matter mechanism to explain the XENON1T excess, analyzing various interaction form factors and deriving new constraints on DM-electron cross sections.

Findings

Sun-heated DM can account for the XENON1T excess.

Inferred DM-electron cross sections range from 10^{-38} to 10^{-42} cm^2.

The scenario provides stronger constraints than previous models.

Abstract

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, $F(q)\propto q^i$ with $i=0,1,2$ and $q$ being the momentum exchange, 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 $\sim 10^{-38}$~cm$^2$ (for $i=0$) to $\sim 10^{-42}$~cm$^2$ (for $i=2$). We also derive constraints on the DM-electron cross sections for different 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.