Dark Matter and the XENON1T electron recoil excess

TL;DR

This paper proposes that the 2 keV electron recoil excess observed by XENON1T can be explained by fast-moving dark matter particles, suggesting exotic physics scenarios involving unusual dark matter dynamics.

Contribution

It introduces a novel explanation for the XENON1T excess involving fast dark matter particles outside the standard cold dark matter halo.

Findings

Fast DM particles can fit the XENON1T excess

Possible origins include DM sub-haloes and relativistic axions

Exotic DM dynamics are required for these scenarios

Abstract

We show that the electron recoil excess around 2 keV claimed by the Xenon collaboration can be fitted by DM or DM-like particles having a fast component with velocity of order $\sim 0.1$. Those particles cannot be part of the cold DM halo of our Galaxy, so we speculate about their possible nature and origin, such as fast moving DM sub-haloes, semi-annihilations of DM and relativistic axions produced by a nearby axion star. Feasible new physics scenarios must accommodate exotic DM dynamics and unusual DM properties.