Minimal Dark Matter Freeze-in with Low Reheating Temperatures and Implications for Direct Detection

TL;DR

This paper explores how low reheating temperatures affect freeze-in dark matter production mediated by an ultralight dark photon, revealing increased coupling and detection prospects in direct detection experiments.

Contribution

It introduces a new regime with low initial temperatures below DM mass, showing the need for larger portal couplings and enhanced detection signals.

Findings

Boltzmann suppression reduces DM production at low temperatures

Larger portal couplings are required to achieve observed relic abundance

Enhanced DM-electron scattering cross sections improve detection prospects

Abstract

We investigate the influence of the reheating temperature of the visible sector on the freeze-in dark matter (DM) benchmark model for direct detection experiments, where DM production is mediated by an ultralight dark photon. Here we consider a new regime for this benchmark: we take the initial temperature of the thermal Standard Model (SM) bath to be below the DM mass. The production rate from the SM bath is drastically reduced due to Boltzmann suppression, necessitating a significant increase in the portal coupling between DM and the SM to match the observed relic DM abundance. This enhancement in coupling strength increases the predicted DM-electron scattering cross section, making freeze-in DM more accessible to current direct detection experiments.