PeV-Scale Dark Matter as a Thermal Relic of a Decoupled Sector

TL;DR

This paper explores a scenario where PeV-scale dark matter, part of a hidden sector, freezes out via annihilation to a lighter state, which then decays to reheat the universe and allow for very heavy dark matter.

Contribution

It introduces a model of heavy dark matter in a decoupled sector with a novel freeze-out and decay mechanism, expanding the viable mass range beyond the weak scale.

Findings

Dark matter can be as heavy as 1-100 PeV without overproduction.

The decay of the metastable state reheat the universe and dilute relics.

Viable parameter space identified for PeV-scale dark matter.

Abstract

In this letter, we consider a class of scenarios in which the dark matter is part of a heavy hidden sector that is thermally decoupled from the Standard Model in the early universe. The dark matter freezes-out by annihilating to a lighter, metastable state, whose subsequent abundance can naturally come to dominate the energy density of the universe. When this state decays, it reheats the visible sector and dilutes all relic abundances, thereby allowing the dark matter to be orders of magnitude heavier than the weak scale. For concreteness, we consider a simple realization with a Dirac fermion dark matter candidate coupled to a massive gauge boson that decays to the Standard Model through its kinetic mixing with hypercharge. We identify viable parameter space in which the dark matter can be as heavy as ~1-100 PeV without being overproduced in the early universe.