Low-reheating temperature dark matter

The freeze-in mechanism offers an alternative to the standard thermal freeze-out paradigm for dark matter production. In this contribution, we review recent advances in freeze-in dark matter production, emphasizing how the issue of gravitational production during inflation and reheating can be resolved and how this resolution leads to new phenomenology in the regime of stronger couplings. We discuss how a prolonged matter-dominated epoch can restore the predictivity of freeze-in by diluting the initially produced gravitational relics. This long matter-dominated epoch in turn leads to low reheating temperatures. We show that this allows freeze-in production at couplings as large as [Formula: see text]. Furthermore, we show that freeze-in at low reheating temperatures can fill the overproduction gap between freeze-in and freeze-out, reproducing the observed dark matter abundance for all couplings between the FIMP and WIMP regimes. This framework has rich phenomenology: it can be probed in current and future direct detection and collider experiments and applies broadly to extensions of the Standard Model.