Xenon-1T excess as a possible signal of a sub-GeV hidden sector dark matter

TL;DR

This paper proposes a new particle physics model involving a dark photon and degenerate fermions to explain the Xenon-1T excess at 2.5 keV, suggesting inelastic dark matter scattering as the cause.

Contribution

It introduces a $U(1)$ extended Standard Model with a dark sector of degenerate fermions and a dark photon, explaining the Xenon-1T excess through inelastic scattering.

Findings

The model accounts for the 2.5 keV excess in Xenon-1T data.

Predictions can be tested with future Xenon-1T and SuperCDMS data.

Abstract

We present a particle physics model to explain the observed enhancement in the Xenon-1T data at an electron recoil energy of 2.5 keV. The model is based on a $U(1)$ extension of the Standard Model where the dark sector consists of two essentially mass degenerate Dirac fermions in the sub-GeV region with a small mass splitting interacting with a dark photon. The dark photon is unstable and decays before the big bang nucleosynthesis, which leads to the dark matter constituted of two essentially mass degenerate Dirac fermions. The Xenon-1T excess is computed via the inelastic exothermic scattering of the heavier dark fermion from a bound electron in xenon to the lighter dark fermion producing the observed excess events in the recoil electron energy. The model can be tested with further data from Xenon-1T and in future experiments such as SuperCDMS.