From WIMP to FIMP during reheating: collider vs non-collider probes for p-wave annihilation

By examining the transition from freeze-out to freeze-in dark matter (DM) production within the framework of perturbative reheating, where DM interacts with the visible sector through effective operators of dimension six, we have investigated how a broad range of new physics probes can reveal the nature of the pre-BBN Universe. Incorporating constraints from direct and indirect DM searches, invisible decay measurements, collider experiments, and gravitational wave observations, our analysis demonstrates that both current and forthcoming experimental sensitivities can serve as powerful tools for probing as well as constraining the post-inflationary era, together with new physics beyond the SM. Our analysis demonstrates that collider experiments at both the intensity and energy frontiers can impose strong bounds on derivative operators whose interactions are typically {\it p-wave suppressed}, and therefore only weakly constrained by astrophysical observations. In particular, these complementary searches can significantly restrict the allowed reheating temperature, DM mass and effective interaction scale required to reproduce the observed DM abundance for DM produced during the epoch of reheating.