Relic densities including Sommerfeld enhancements in the MSSM

TL;DR

This paper introduces a comprehensive formalism for calculating Sommerfeld enhancement effects in multi-state fermion systems and applies it to improve relic density predictions for neutralino dark matter in the MSSM, revealing significant density suppression in certain parameter regions.

Contribution

It presents a novel, general method to include Sommerfeld enhancements in relic density calculations for multi-state fermion systems, specifically applied to the MSSM neutralinos.

Findings

Relic density can be suppressed by a factor of a few in certain parameter regions.

Significant density suppression occurs for Wino-like neutralinos around a few TeV.

Resonance effects can lead to an order of magnitude reduction in relic density.

Abstract

We have developed a general formalism to compute Sommerfeld enhancement (SE) factors for a multi-state system of fermions, in all possible spin configurations and with generic long-range interactions. We show how to include such SE effects in an accurate calculation of the thermal relic density for WIMP dark matter candidates. We apply the method to the MSSM and perform a numerical study of the relic abundance of neutralinos with arbitrary composition and including the SE due to the exchange of the W and Z bosons, photons and Higgses. We find that the relic density can be suppressed by a factor of a few in a seizable region of the parameter space, mostly for Wino-like neutralino with mass of a few TeV, and up to an order of magnitude close to a resonance.