$Z^\prime$-mediated dark matter freeze-in at stronger coupling

Abstract

We study freeze-in production of fermionic dark matter mediated by a $Z^\prime$ gauge boson. In particular, we explore the regime of Boltzmann-suppressed production, when the Standard Model (SM) thermal bath temperature never exceeds the dark matter mass. The corresponding gauge coupling is then required to be significant, up to order one. As a result, this class of freeze-in models can be probed by the current and future direct dark matter detection experiments.