Self-interacting inelastic dark matter in the light of XENON1T excess

Abstract

We propose a self-interacting inelastic dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. Two quasidegenerate Majorana fermion DM particles interact within themselves via a light hidden sector massive gauge boson and with the standard model particles via gauge kinetic mixing. We also consider an additional long-lived singlet scalar, which helps in realizing correct dark matter relic abundance via a hybrid setup comprising both freeze-in and freeze-out mechanisms. While being consistent with the required DM phenomenology along with sufficient self-interactions to address the small-scale issues of cold dark matter, the model with GeV-scale DM can explain the XENON1T excess via inelastic down-scattering of the heavier DM component into the lighter one. All these requirements leave a very tiny parameter space, keeping the model very predictive for near-future experiments.