From WIMPs to FIMPs with 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.

Confronting dark matter freeze-in during reheating with constraints from inflation

“…In particular, in this study, we investigate scenarios of bosonic and fermionic reheating, where the inflaton decays dominant into pairs of bosons or fermions. Such cosmological histories have been recently considered in the context of DM freeze-in with (non-)renormalizable operators [20,21,[32][33][34][35][36][37], WIMPs [38], in the singlet-scalar DM model [39], CMB constraints on DM production [40][41][42][43], and freeze-in Baryogenesis [44].…”