Inelastic Dark Matter Electron Scattering and the XENON1T Excess

TL;DR

This paper explores how inelastic scattering of dark matter particles mediated by a dark photon can explain the XENON1T electron recoil excess, highlighting a viable parameter space for this scenario.

Contribution

It introduces a model of inelastic dark matter scattering via a dark photon that can account for the XENON1T excess, considering atomic effects and small mass splittings.

Findings

Enhanced scattering rate due to small mass splitting.

Viable parameter space matching the XENON1T excess.

Explanation of electron recoil energies around 2-3 keV.

Abstract

Detection of electron recoils by dark matter (DM) may reveal the structure of the dark sector. We consider a scenario where a heavier DM particle inelastically scatters off an electron and is converted into a lighter DM particle. A small mass difference between the two DM particles is transferred into electron recoil energy. We investigate the DM-electron interaction mediated by a massive dark photon and evaluate the inelastic DM scattering rate, taking account of the atomic structure. It is found that the scattering rate is significantly enhanced because of the small mass splitting, which allows for a small momentum transfer matched with the size of the electron wave function. We show that there exists a viable parameter space which explains the excess of electron recoil events around 2-3 keV recently reported by the XENON1T experiment.