Higgs portal vector dark matter at a low reheating temperature

Abstract

In this study, we explore vector dark matter (DM) production in the early Universe focusing on a scenario with a low reheating temperature. One can achieve low reheat temperature in many ways, for example, by considering a longer lifetime of the inflaton field. We analyze the impact of various model parameters on DM production, including gauge coupling and reheat temperature, while incorporating all relevant constraints from DM relic density, collider bounds, and DM direct and indirect detection experiments. Our results reveal a strong correlation between DM mass and reheat temperature, with viable parameter space requiring $T_R/M_{W_D} \sim 0.1$. While DM production from decays is generally subdominant, we identify a regime where freeze-in production from decay is dominant due to the phase space suppression. For DM masses below 100 GeV, production is primarily driven by SM fermions, whereas higher masses come due to the Higgses annihilation. The enhanced coupling strength in our framework enables potential detection in direct and indirect detection and collider experiments. The direct detection experiments have already explored some parts of the region and future DARWIN will explore the further region whereas for indirect detection, the detection prospects for the present case are futile. We found that a very narrow region of the parameter space has been explored by the DM direct detection contrary to the WIMP DM case where most of the parameter space has been ruled out.