Dark matter and the XENON1T electron recoil excess

Abstract

We show that the electron recoil excess around 2 keV claimed by the Xenon Collaboration can be fitted by dark matter (DM) or DM-like particles having a fast component with velocity of order ∼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 subhalos, semiannihilations of DM and relativistic axions produced by a nearby axion star. Feasible new physics scenarios must accommodate exotic DM dynamics and unusual DM properties.