Reviving $Z$ and Higgs Mediated Dark Matter Models in Matter Dominated
  Freeze-out
  It is quite conceivable that dark matter freeze-out occurred during an early
period of matter domination, in which case the evolution and relic abundance
differ from standard freeze-out calculations which assume a radiation dominated
universe. Here we re-examine the classic models in which dark matter
interactions with the Standard Model are mediated via either the Higgs or $Z$
boson in the context of matter dominated freeze-out. We highlight that while
these classic models are largely excluded by searches in the radiation
dominated case, matter dominated freeze-out can relax these limits and thus
revive the Higgs and $Z$ portals. Additionally, we discuss the distinctions
between matter dominated freeze-out and decoupling during the transition from
matter domination to radiation domination, and we comment on the parameter
regimes which lead to non-negligible dark matter production during this
transition.
