Probing low-reheating scenarios with freeze-in dark matter

The feebly-interacting massive particle (FIMP) paradigm offers an intriguing
solution to the dark matter (DM) puzzle, with FIMPs produced via the
freeze-in mechanism due to extremely weak interactions with the standard
model (SM) plasma. After reviewing the basics of the freeze-in production,
this talk explores how reheating dynamics after cosmic inflation affects DM
production, focusing on matter-domination and kination scenarios. While
instantaneous reheating is often assumed, this simplification breaks down
for reheating temperatures comparable to or below the DM production scale.
In such cases, the equation-of-state parameter of the inflaton and the
scaling of the SM temperature during reheating become crucial. Low reheating
temperature scenarios necessitate stronger couplings between the dark and
visible sectors to reproduce the observed DM relic abundance, thereby
enlarging the parameter space regions probed by current and future DM
experiments.