Higgs portal dark matter in non-thermal cosmologies

TL;DR

This paper explores Higgs portal dark matter within non-thermal cosmologies, demonstrating its viability across various masses and couplings, especially with late-time matter domination scenarios, and discusses potential experimental signatures.

Contribution

It introduces a non-thermal cosmological framework allowing Higgs portal dark matter to evade previous constraints, expanding viable parameter space especially for sub-GeV masses.

Findings

Dark matter < GeV is possible without hidden sectors.

Late-time matter domination enables viable Higgs portal dark matter.

Future experiments can probe significant parameter space.

Abstract

A scalar particle with a relic density set by annihilations through a Higgs portal operator is a simple and minimal possibility for dark matter. However, assuming a thermal cosmological history this model is ruled out over most of parameter space by collider and direct detection constraints. We show that in theories with a non-thermal cosmological history Higgs portal dark matter is viable for a wide range of dark matter masses and values of the portal coupling, evading existing limits. In particular, we focus on the string theory motivated scenario of a period of late time matter domination due to a light modulus with a decay rate that is suppressed by the Planck scale. Dark matter with a mass < GeV is possible without additional hidden sector states, and this can have astrophysically relevant self-interactions. We also study the signatures of such models at future direct, indirect, and collider experiments. Searches for invisible Higgs decays at the high luminosity LHC or an e+ e- collider could cover a significant proportion of the parameter space for low mass dark matter, and future direct detection experiments will play a complementary role.