WIMPs during Reheating

TL;DR

This paper explores how WIMP dark matter particles can undergo thermal freeze-out during the reheating phase after inflation, revealing new parameter spaces and implications for dark matter detection.

Contribution

It investigates WIMP freeze-out during reheating with a generic inflaton potential, showing enlarged viable parameter space and lower annihilation cross-sections compared to standard models.

Findings

Reheating phase affects WIMP freeze-out dynamics.

Entropy injection during reheating broadens viable dark matter parameters.

Lower annihilation cross-sections are compatible with observed relic abundance.

Abstract

Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. In the standard scenario where the freeze-out occurs well after the end of inflationary reheating, they are in tension with the severe experimental constraints. Here, we investigate the thermal freeze-out of WIMPs occurring {\it during} reheating, while the inflaton $\phi$ coherently oscillates in a generic potential $\propto \phi^n$. Depending on the value of $n$ and the spin of the inflaton decaying products, the evolution of the radiation and inflaton energy densities can show distinct features, therefore, having a considerable impact on the freeze-out behavior of WIMPs. As a result of the injection of entropy during reheating, the parameter space compatible with the observed DM relic abundance is enlarged. In particular, the WIMP thermally averaged annihilation cross-section can be several magnitudes lower than that in the standard case. Finally, we discuss the current bounds from dark matter indirect detection experiments, and explore future challenges and opportunities.