Prethermalization production of dark matter

Abstract

At the end of inflation, the inflaton field decays into an initially non-thermal population of relativistic particles which eventually thermalize. We consider the production of dark matter from this relativistic plasma, focusing on the pre-thermal phase. We find that for a production cross-section $\sigma (E)\sim E^n$ with $n>2$, the present dark matter abundance is produced during the pre-thermal phase of its progenitors. For $n\le 2$, entropy production during reheating makes the non-thermal contribution to the present dark matter abundance sub-dominant compared to that produced thermally. As specific examples, we verify that the non-thermal contribution is irrelevant for gravitino production in low scale supersymmetric models ($n=0$), and is dominant for gravitino production in high scale supersymmetry models ($n=6$).