On finite density effects on cosmic reheating and moduli decay and implications for Dark Matter production

TL;DR

This paper investigates how finite density effects influence the damping of scalar fields like the inflaton or moduli, significantly impacting the universe's thermal history and dark matter production.

Contribution

It provides new analytic and numerical estimates of the maximal and reheating temperatures considering finite density corrections.

Findings

Finite density effects can greatly increase the maximal and reheating temperatures.

Enhanced temperatures can lead to higher dark matter abundance than previously estimated.

Analytic estimates are validated through numerical simulations.

Abstract

We study the damping of an oscillating scalar field in a Friedmann-Robertson-Walker spacetime by perturbative processes, taking into account the finite density effects that interactions with the plasma of decay products have on the damping rate. The scalar field may be identified with the inflaton, in which case this process leads to the reheating of the universe after inflation. It can also resemble a modulus that dominates the energy density of the universe at later times. We find that the finite density corrections to the damping rate can have a drastic effect on the thermal history and considerably increase both, the maximal temperature in the early universe and the reheating temperature at the onset of the radiation dominated era. As a result abundance of some Dark Matter candidates may be considerably larger than previously estimated. We give improved analytic estimates for the maximal and the reheating temperatures and confirm them numerically in a simple model.