Dark Matter Production in an Early Matter Dominated Era

TL;DR

This paper explores how an early matter-dominated era affects dark matter production, considering various production mechanisms and temperature-dependent effects, revealing new parameter space regions and bounds on particle masses.

Contribution

It provides a detailed analysis of dark matter production during an early matter-dominated era, including direct decay contributions and temperature-dependent effects on relic density.

Findings

Additional parameter space regions with correct DM relic density identified.

Temperature dependence of $g_*$ can significantly alter DM density.

Upper bounds on long-lived particle mass derived for non-thermal DM scenarios.

Abstract

We investigate dark matter (DM) production in an early matter dominated era where a heavy long-lived particle decays to radiation and DM. In addition to DM annihilation into and thermal DM production from radiation, we include direct DM production from the decay of the long-lived particle. In contrast to earlier treatments the temperature dependence of the number of degrees of freedom $g_*$ in the Standard Model (SM) plasma is treated carefully. Besides the well-known cases of thermal hot and cold DM, additional regions of parameter space with the approximately correct DM relic density appear. In some of these regions the temperature dependence of $g_*$ can change the final DM density by several hundred percent. Furthermore, we analyze the effect of allowing nonvanishing initial abundances for radiation and DM. We find an upper bound on the mass of the long-lived particle if the DM annihilation cross section is below that corresponding to thermal WIMP (Weakly Interactive Massive Particle) DM in standard cosmology.