Enhancement of the Dark Matter Abundance Before Reheating: Applications to Gravitino Dark Matter

TL;DR

This paper investigates how particle production at high temperatures during the early stages of reheating affects the final abundance of dark matter particles, with implications for gravitino dark matter in various supersymmetric models.

Contribution

It analyzes the impact of early particle production on dark matter abundance considering different temperature dependencies of production cross sections, highlighting when enhancement or dilution occurs.

Findings

For n<6, early production is diluted by later entropy generation.

For n≥6, early production leads to a significant enhancement in particle abundance.

Implications for gravitino dark matter vary with supersymmetry scale and temperature dependence.

Abstract

In the first stages of inflationary reheating, the temperature of the radiation produced by inflaton decays is typically higher than the commonly defined reheating temperature $T_{RH} \sim (\Gamma_\phi M_P)^{1/2}$ where $\Gamma_\phi$ is the inflaton decay rate. We consider the effect of particle production at temperatures at or near the maximum temperature attained during reheating. We show that the impact of this early production on the final particle abundance depends strongly on the temperature dependence of the production cross section. For $\langle \sigma v \rangle \sim T^n/M^{n+2}$, and for $n < 6$, any particle produced at $T_{\rm max}$ is diluted by the later generation of entropy near $T_{RH}$. This applies to cases such as gravitino production in low scale supersymmetric models ($n=0$) or NETDM models of dark matter ($n=2$). However, for $n\ge6$ the net abundance of particles produced during reheating is enhanced by over an order of magnitude, dominating over the dilution effect. This applies, for instance to gravitino production in high scale supersymmetry models where $n=6$.