Sub-MeV Self Interacting Dark Matter

Abstract

In this paper, we present a model for sub-MeV dark matter with strong self-interactions which can solve some of the small-scale crisis of the Λ⁢CDM. The dark matter is a Majorana fermion with only off-diagonal interactions with a hidden 𝑈⁢(1)𝐷 gauge boson. The relic density is obtained by freeze-out of Boltzmann suppressed annihilations to a light fermionic species. The self-interaction is a one-loop process and constrained to be between 0.1 to 1 cm2/g. Severe constraints from the BBN on 𝑁eff require that the dark and visible sector are not in thermal equilibrium during freeze-out. The effect of this temperature asymmetry is studied.