Structure Formation Constraints on Sommerfeld-Enhanced Dark Matter Annihilation

TL;DR

This paper investigates how Sommerfeld-enhanced dark matter annihilation affects cosmic structure growth, setting upper limits on the annihilation cross-section and exploring implications for dark matter models and cosmic microwave background data.

Contribution

It provides the first constraints on Sommerfeld-enhanced dark matter annihilation using structure formation data, considering relativistic species from dark matter annihilation.

Findings

No evidence for Sommerfeld-enhanced dark matter annihilation

Derived upper limits on the annihilation cross-section

Explored potential origin of relativistic species from dark matter

Abstract

We study the growth of cosmic structure under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic species that only interacts gravitationally with the standard model. This assumption also allows us to test whether the additional relativistic species mildly favored by cosmic-microwave background data could originate from dark matter annihilation. We do not find evidence for Sommerfeld-enhanced dark matter annihilation and derive the corresponding upper limits on the annihilation cross-section.