Speaker
Description
Future high-energy $e^+e^-$ colliders offer an unprecedented opportunity to explore dark matter scenarios with feeble interactions that remain inaccessible to current hadron colliders. In this presentation, we demonstrate how future lepton colliders can not only discover such dark matter candidates but also probe the thermal history of the Universe. We investigate two scenarios: (1) ultraviolet freezing-in dark matter, and (2) non-standard freezing-out dark matter scenarios, in which the relic abundance is established during the reheating epoch, rendering it sensitive to the reheating temperature and dynamics. Considering effective interactions between Dark Matter and the Standard Model, we analyze multiple collider signatures including mono-$\gamma$, dilepton, and mono-$h$ plus missing energy channels at future high-energy International Linear Collider runs with polarized and unpolarized beams. We show that these clean experimental environments enable sensitivity to the feeble couplings responsible for the observed relic abundance. Combining collider observables with cosmological constraints, we demonstrate that collider measurements can indirectly constrain the reheating temperature, distinguish different reheating dynamics, and identify viable cosmological histories. Our results demonstrate the capability of future linear colliders to bridge particle physics and cosmology, transforming precision collider measurements into powerful probes of physics beyond the Standard Model.