Probing low-reheating scenarios with minimal freeze-in dark matter

TL;DR

This paper investigates how different reheating scenarios in the early universe affect the production of minimal freeze-in dark matter, highlighting the importance of quantum statistics and cosmic dynamics in determining detectable parameter spaces.

Contribution

It provides a detailed analysis of dark matter production during various reheating phases, extending beyond the instantaneous approximation to include matter-domination and kination effects.

Findings

Reheating dynamics significantly influence dark matter relic abundance.

Low-temperature reheating enhances dark matter coupling requirements.

Next-generation experiments will probe broader parameter regions.

Abstract

The parameter space of freeze-in dark matter (DM) with mass $m_\chi$ through light dark photon (``minimal freeze-in DM'') is currently being probed by direct detection experiments through electron and nuclear recoil. Exploring the DM production in the mass range $10^{-2}~{\rm MeV} < m_\chi < 10^3$ TeV, we quantify the impact of quantum statistics and the reheating dynamics (beyond the instantaneous reheating approximation) on the DM production in the early universe, in particular, the dependence on the cosmic equation of state and the scaling of the temperature of the Standard Model bath during reheating. Special cases corresponding to matter-domination and kination are carefully studied. To fit the entire observed DM relic abundance, low-temperature reheating scenarios require an increase in the coupling between dark and visible sectors which, in turn, enhances the regions of the parameter space that are already tested and will be probed by next-generation direct detection experiments for diverse reheating scenarios.