SIMPs through the axion portal

TL;DR

This paper proposes a model where SIMP dark matter interacts via an axion-like particle, maintaining thermal equilibrium and satisfying observational constraints, with promising experimental prospects for detection.

Contribution

It introduces a novel mechanism for SIMP dark matter to stay in equilibrium using an axion-like portal, expanding the viable parameter space for such models.

Findings

Viable parameter space with axion-like particles near the SIMP mass

Strong constraints from experiments and astrophysical observations

Upcoming experiments will probe the predicted parameter space

Abstract

Dark matter could be a thermal relic comprised of strongly interacting massive particles (SIMPs), where $3 \rightarrow 2$ interactions set the relic abundance. Such interactions generically arise in theories of chiral symmetry breaking via the Wess-Zumino-Witten term. In this work, we show that an axion-like particle can successfully maintain kinetic equilibrium between the dark matter and the visible sector, allowing the requisite entropy transfer that is crucial for SIMPs to be a cold dark matter candidate. Constraints on this scenario arise from beam dump and collider experiments, from the cosmic microwave background, and from supernovae. We find a viable parameter space when the axion-like particle is close in mass to the SIMP dark matter, with strong-scale masses of order a few hundred MeV. Many planned experiments are set to probe the parameter space in the near future.