Strong constraints on self-interacting dark matter with light mediators

TL;DR

This paper demonstrates that models coupling dark matter to light mediators, which produce velocity-dependent self-interactions, face strong constraints from cosmic observations due to Sommerfeld-enhanced annihilation, ruling out key parameter spaces.

Contribution

It provides a detailed analysis of Sommerfeld enhancement effects in dark matter models with light mediators and derives constraints from cosmic microwave background and indirect detection data.

Findings

Constraints exclude large self-interaction parameter space for s-wave annihilation

Sommerfeld effect significantly enhances annihilation rates

Models addressing small-scale structure problems are strongly constrained

Abstract

Coupling dark matter to light new particles is an attractive way to combine thermal production with strong velocity-dependent self-interactions. Here we point out that in such models the dark matter annihilation rate is generically enhanced by the Sommerfeld effect, and we derive the resulting constraints from the Cosmic Microwave Background and other indirect detection probes. For the frequently studied case of s-wave annihilation these constraints exclude the entire parameter space where the self-interactions are large enough to address the small-scale problems of structure formation.