From WIMPs to FIMPs with Low Reheating Temperatures

TL;DR

This paper explores how low reheating temperatures after inflation influence the production of dark matter particles via WIMP and FIMP mechanisms, highlighting the impact of reheating details on dark matter genesis and experimental detectability.

Contribution

It demonstrates the transition between WIMP and FIMP regimes at low reheating temperatures and provides a numerical analysis of the singlet-scalar dark matter model under these conditions.

Findings

Reheating temperature affects dark matter production mechanisms.

FIMP regions are testable by current direct detection experiments.

Transition between WIMP and FIMP regimes is smooth at low reheating temperatures.

Abstract

Weakly- and Feebly-Interacting Massive Particles (WIMPs and FIMPs) are among the best-motivated dark matter (DM) candidates. In this paper, we investigate the production of DM through the WIMP and FIMP mechanisms during inflationary reheating. We show that the details of the reheating, such as the inflaton potential and the reheating temperature, have a strong impact on the genesis of DM. The strong entropy injection caused by the inflaton decay has to be compensated by a reduction of the portal coupling in the case of WIMPs, or by an increase in the case of FIMPs. We pinpoint the smooth transition between the WIMP and the FIMP regimes in the case of low reheating temperature. As an example, we perform a full numerical analysis of the singlet-scalar DM model; however, our results are generic and adaptable to other particle DM candidates. Interestingly, in the singlet-scalar DM model with low-reheating temperature, regions favored by the FIMP mechanism are already being tested by direct detection experiments such as LZ and XENONnT.