Fingerprints of freeze-in dark matter in an early matter-dominated era
  We study the impact of an alternate cosmological history with an early
matter-dominated epoch on the freeze-in production of dark matter. Such early
matter domination is triggered by a meta-stable matter field dissipating into
radiation. In general, the dissipation rate has a non-trivial temperature and
scale factor dependence. Compared to the usual case of dark matter production
via the freeze-in mechanism in a radiation-dominated universe, in this
scenario, orders of magnitude larger coupling between the visible and the dark
sector can be accommodated. Finally, as a proof of principle, we consider a
specific model where the dark matter is produced by a sub-GeV dark photon
having a kinetic mixing with the Standard Model photon. We point out that the
parameter space of this model can be probed by the experiments in the presence
of an early matter-dominated era.
