Freeze-in at stronger coupling

The predictivity of many nonthermal dark matter (DM) models is marred by the gravitational production background. Nevertheless, if the reheating temperature <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>T</a:mi><a:mi>R</a:mi></a:msub></a:math> is low, the gravitationally produced relics can be diluted. We study the freeze-in dark matter production mechanism at temperatures below the dark matter mass. In this case, the coupling to the thermal bath has to be significant to account for the observed dark matter relic density. As a result, the direct DM detection experiments already probe such freeze-in models, excluding significant parts of parameter space. Published by the American Physical Society 2024