Freeze-in dark matter in EDGES 21-cm signal

Abstract

The first measurement on temperature of hydrogen 21-cm signal reported by EDGES strongly favors Coulomb-like interaction between freeze-in dark matter and baryon fluid. We investigate such dark matter both in one- and two-component context, with the light force carrier(s) essential for the Coulomb-like interaction not being photon. Using a conversion of cross sections used by relevant experiments and Boltzmann equations to encode effects of the dark matter-baryon interaction, we show that both cases are robustly excluded by the stringent stellar cooling bounds in the sub-GeV dark matter mass range. The exclusion of one-component case applies to simplified freeze-in dark matter with the light force carrier as dark photon, gauged $B-L$, $L_{e}-L_{\mu}$,$L_{e}-L_{\tau}$ or axion-like particle, while the exclusion of two-component case applies to simplified freeze-in dark matter with the two light force carriers as two axion-like particles coupled to standard model quarks and leptons respectively.