A dark matter solution for the XENON1T electron excess and the galactic center 511 keV line

Abstract

The excess of the 511 keV line from the Milky Way galactic bulge, confirmed by the INTEGRAL detector, is a longstanding mystery. The morphology of the line appears to be proportional to the square of the dark matter density, hinting towards a dark matter origin. On the other hand, in 2020, XENON1T has reported an excess of electrons with a recoil energy of $2-4$ keV. We present a model based on a dark matter of a few MeV mass that decays into a pair of pico-charged particles with a lifetime much larger than the age of the Universe. The magnetic field of the galaxy accumulates these relativistic pico-charged particles whose scattering on the electrons can explain the signal reported by XENON1T. The annihilation of the pico-charged particles in the galactic bulge leads to $e^-e^+$ production and therefore to an excess of the 511 keV line. We review the present observational bounds and the strategies to test the model.