Pico-charged particles explaining 511 keV line and XENON1T signal

Abstract

There is a robust signal for a 511 keV photon line from the galactic center which may originate from dark matter particles with masses of a few MeV. To avoid the bounds from delayed recombination and from the absence of the line from dwarf galaxies, in 2017, we have proposed a model in which dark matter first decays into a pair of intermediate pico-charged particles $C\bar{C}$ with a lifetime much larger than the age of the universe. The galactic magnetic field accumulates the relativistic $C\bar{C}$ that eventually annihilate, producing the $e^-e^+$ pair that give rise to the 511 keV line. The relativistic pico-charged $C$ particles can scatter on the electrons inside the direct dark matter search detectors imparting a recoil energy of $E_r \sim$~keV. We show that this model can account for the electron recoil excess recently reported by the XENON1T experiment. Moreover, we show that the XENON1T electron recoil data sets the most stringent bound on the lifetime of the dark matter within this model.