Evidence of a simple dark sector from XENON1T excess

TL;DR

This paper suggests that dark photons from annihilating keV dark fermions could explain the XENON1T electron recoil excess, fitting within existing stellar cooling constraints and accounting for a small fraction of dark matter.

Contribution

It introduces a minimal $U(1)_X$ gauge extension model where dark photons explain the XENON1T excess, compatible with stellar cooling bounds and dark matter relic density.

Findings

Dark photons can induce the XENON1T excess.

Model parameters fit stellar cooling constraints.

Dark fermions contribute >1% to DM relic density.

Abstract

We propose that the nearly massless dark photons produced from the annihilation of keV dark fermions in the Galaxy can induce the excess of electron recoil events recently observed in the XENON1T experiment. The minimal model for this is the extension of a $U(1)_{X}$ gauge symmetry, under which the dark photon couples to both dark and visible matter currents. We find that the best-fit parameters of the dark sector are compatible with the most stringent constraints from stellar cooling. We also show that in the freeze-out scenario, the dark fermions can explain the anomaly while contributing $\gtrsim 1\%$ of the DM relic density.