Self-interacting dark matter with a stable vector mediator

TL;DR

This paper explores a model of self-interacting dark matter with a stable vector mediator that can address small-scale structure issues without conflicting with cosmic microwave background constraints.

Contribution

It demonstrates that a stable vector mediator can produce velocity-dependent dark matter self-interactions while remaining consistent with cosmological bounds.

Findings

Viable parameter space for stable vector mediators exists.

Self-interactions can solve small-scale structure problems.

Model remains consistent with CMB and BBN constraints.

Abstract

Light vector mediators can naturally induce velocity-dependent dark matter self-interactions while at the same time allowing for the correct dark matter relic abundance via thermal freeze-out. If these mediators subsequently decay into Standard Model states such as electrons or photons however, this is robustly excluded by constraints from the Cosmic Microwave Background. We study to what extent this conclusion can be circumvented if the vector mediator is stable and hence contributes to the dark matter density while annihilating into lighter degrees of freedom. We find viable parts of parameter space which lead to the desired self-interaction cross section of dark matter to address the small-scale problems of the collisionless cold dark matter paradigm while being compatible with bounds from the Cosmic Microwave Background and Big Bang Nucleosynthesis observations.