Gravitational SIMPs

TL;DR

This paper investigates how thermalization and number-changing processes in the dark sector influence gravitationally produced dark matter, expanding viable parameter space and considering different dark matter spins and a specific scalar model.

Contribution

It provides a model-independent analysis of how dark matter self-interactions affect the relic abundance and viable parameter space in gravitational production scenarios.

Findings

Self-interactions enlarge the viable parameter space.

Lower reheating temperatures can produce correct relic abundance.

Results are applicable to scalar, fermion, and vector dark matter.

Abstract

We study the impact of thermalization and number-changing processes in the dark sector on the yield of gravitationally produced dark matter (DM). We take into account the DM production through the $s$-channel exchange of a massless graviton both from the scattering of inflatons during the reheating era, and from the Standard Model bath via the UV freeze-in mechanism. By considering the DM to be a scalar, a fermion, and a vector boson we show, in a model-independent way, that DM self-interaction gives rise to a larger viable parameter space by allowing lower reheating temperature to be compatible with Planck observed relic abundance. As an example, we also discuss our findings in the ontext of the $\mathbb{Z}_2$-symmetric scalar singlet DM model.