Probing High Reheating Temperatures by Direct Detection Experiments

TL;DR

This paper shows that direct detection experiments can probe high reheating temperatures in the early universe by considering both gravitational and dark photon mediated production of dark matter, revealing new sensitivity to cosmological history.

Contribution

It introduces a combined UV and IR freeze-in framework for dark matter production, highlighting the impact of high reheating temperatures on direct detection signals.

Findings

Current experiments exclude the benchmark model over a wide mass range.

Gravitational production relaxes the coupling constraints needed for relic abundance.

Experiments now indirectly probe the universe's reheating temperature.

Abstract

We argue that the benchmark freeze in dark matter (DM) scenario for direct detection experiments, in which a DM candidate interacts with the Standard Model (SM) through an ultralight dark photon, becomes sensitive to the visible sector reheating temperature if it is sufficiently high. At such temperatures, the irreducible ultraviolet (UV) freeze in production of DM through graviton exchange becomes important and must be combined with the infrared (IR) freeze in yield mediated by the dark photon. As long as gravitationally produced DM does not equilibrate through annihilation into dark photons and the subsequent formation of a dark thermal bath, it retains information about the reheating phase. Including this gravitational contribution relaxes the required DM and SM portal coupling and allows smaller values than those that would match the observed relic abundance through IR freeze in alone. Since current direct detection experiments have excluded the benchmark freeze in model over a wide range of DM masses, they are now effectively probing high reheating temperatures and the gravitational freeze in of DM.