Reviving $Z$ and Higgs Mediated Dark Matter Models in Matter Dominated Freeze-out

TL;DR

This paper revisits Higgs and Z mediated dark matter models assuming an early matter dominated universe, showing that such conditions can relax experimental constraints and revive these models which are otherwise excluded.

Contribution

It demonstrates that matter dominated freeze-out alters dark matter relic abundance calculations, reviving Higgs and Z portal models previously excluded under radiation domination assumptions.

Findings

Matter dominated freeze-out relaxes experimental limits on Higgs and Z portal models.

Classic models are largely excluded in radiation era but viable in matter dominated scenarios.

Transition effects from matter to radiation domination can significantly influence dark matter production.

Abstract

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.