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.
Highlights
Dark matter (DM) comprises the majority of the matter budget of the Universe, but its microphysical properties and origin remain unknown
We show that an axionlike 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
We find a viable parameter space when the axionlike particle is close in mass to the SIMP dark matter, with strong-scale masses of order a few hundred MeV
Summary
Dark matter (DM) comprises the majority of the matter budget of the Universe, but its microphysical properties and origin remain unknown. The number density of WIMPs is set by 2 → 2 annihilations of the DM into standard model (SM) particles, and the observed DM relic abundance is achieved when both the DM mass and coupling to SM particles are near the scales relevant for electroweak processes. [1] where 3 → 2 DM self-interactions set its abundance In this scenario, the observed relic density indicates that the DM mass and self-coupling should be near the strong scale. The observed relic density indicates that the DM mass and self-coupling should be near the strong scale This mechanism of strongly interacting massive particles. In addition to providing a novel thermal mechanism for explaining the dark matter abundance, SIMPs offer a possible explanation for issues related to small-scale structure formation.
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