Thermal Dark Matter From A Highly Decoupled Sector

TL;DR

This paper explores how highly decoupled dark sectors can produce heavy thermal dark matter through late decays and reheating, expanding viable mass ranges beyond traditional WIMP models.

Contribution

It provides a systematic analysis of cosmological histories allowing very heavy dark matter via decays and reheating in decoupled sectors.

Findings

Heavy dark matter (~PeV) can achieve correct relic abundance in decoupled sectors.

Decays of long-lived dark sector particles can reheat the visible universe and dilute dark matter.

Parameter space exists for heavy dark matter with various portal interactions.

Abstract

It has recently been shown that if the dark matter is in thermal equilibrium with a sector that is highly decoupled from the Standard Model, it can freeze-out with an acceptable relic abundance, even if the dark matter is as heavy as ~1-100 PeV. In such scenarios, both the dark and visible sectors are populated after inflation, but with independent temperatures. The lightest particle in the dark sector will be generically long-lived, and can come to dominate the energy density of the universe. Upon decaying, these particles can significantly reheat the visible sector, diluting the abundance of dark matter and thus allowing for dark matter particles that are much heavier than conventional WIMPs. In this paper, we present a systematic and pedagogical treatment of the cosmological history in this class of models, emphasizing the simplest scenarios in which a dark matter candidate annihilates into hidden sector particles which then decay into visible matter through the vector, Higgs, or lepton portals. In each case, we find ample parameter space in which very heavy dark matter particles can provide an acceptable thermal relic abundance. We also discuss possible extensions of models featuring these dynamics.