Dark Matter Freeze-out During Matter Domination

TL;DR

This paper explores how dark matter freeze-out dynamics are altered during a matter-dominated era, affecting relic density calculations and requiring different particle properties than in standard radiation-dominated scenarios.

Contribution

It provides a detailed analysis of dark matter freeze-out during matter domination, highlighting the impact on relic density and particle parameters, which differs from conventional models.

Findings

Freeze-out during matter domination changes the Hubble rate and dynamics.

Decay of the dominant species affects dark matter relic density.

Masses and couplings for dark matter can differ significantly from radiation-dominated cases.

Abstract

We highlight the general scenario of dark matter freeze-out whilst the energy density of the universe is dominated by a decoupled non-relativistic species. Decoupling during matter domination changes the freeze-out dynamics, since the Hubble rate is parametrically different for matter and radiation domination. Furthermore, for successful Big Bang Nucleosynthesis the state dominating the early universe energy density must decay, this dilutes (or repopulates) the dark matter. As a result, the masses and couplings required to reproduce the observed dark matter relic density can differ significantly from radiation dominated freeze-out.