Probing High Reheating Temperatures by Direct Detection Experiments

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.

Figures (2)

• Figure 1: The DM-electron cross section for sub-GeV freeze-in DM, when gravitational production at reheating is included. For $m_\chi\ll T_{\rm rh}\ll10^{17}\,{\rm GeV}$, UV freeze-in production is negligible, and we obtain the standard IR freeze-in benchmark (black solid line), which is taken from Ref. Essig:2011nj. For $T_{\rm rh}\gtrsim 10^{17}\,{\rm GeV}$, the gravitational contribution increases and leads to a smaller DM-electron cross section. Consequently, the freeze-in scenario can extend to values below the black solid line (black dashed lines). The black dotted line corresponds to couplings that would produce $10\%$ of the final DM abundance via IR freeze-in (the remaining $90\%$ of the DM abundance is produced gravitationally). The gray shaded regions display exclusion limits from DAMIC-M DAMIC-M:2025luv and PandaX-4T Zhang:2025ajc experiments.
• Figure 2: The DM-SM coupling for GeV-TeV freeze-in DM by including gravitational production at reheating. For $m_\chi\ll T_{\rm rh}\ll10^{15}\,{\rm GeV}$, UV freeze-in production is insignificant, and we recover the standard IR freeze-in benchmark (black solid line), which is taken from Ref. Bhattiprolu:2023akk. For higher $T_{\rm rh}$, the gravitational contribution leads to a smaller coupling (black dashed lines). The black dotted line is described in the same way as in Fig \ref{['fig:1']}. We plot the current exclusion limits from XENON1T XENON:2018voc and LUX–ZEPLIN (LZ) LZ:2024zvo experiments, using the recast LZ constraints from Ref. Bernal:2024ndy, in gray shades.