Gamma-ray Signals from Dark Matter Annihilation Via Charged Mediators

TL;DR

This paper analyzes gamma-ray signals from Majorana dark matter annihilation via charged mediators, deriving general spectra and ratios for gamma-ray lines, with implications for MSSM dark matter searches.

Contribution

It provides the most general gamma-ray spectrum for internal bremsstrahlung considering fermion mass, mixing, and CP violation, and explores the impact on dark matter detection.

Findings

Derived the general spectrum for internal bremsstrahlung.

Analyzed the ratio of gamma-ray line cross sections as a function of model parameters.

Applied results to constrain MSSM dark matter models.

Abstract

We consider a simplified model in which Majorana fermion dark matter annihilates to charged fermions through exchange of charged mediators. We consider the gamma-ray signals arising from the processes $XX \rightarrow \bar f f \gamma$, $\gamma \gamma$, and $\gamma Z$ in the most general case, including non-trivial fermion mass and non-trivial left-right mixing and $CP$-violating phase for the charged mediators. In particular, we find the most general spectrum for internal bremsstrahlung, which interpolates between the regimes dominated by virtual internal bremsstrahlung and by final state radiation. We also examine the variation in the ratio $\sigma(\gamma \gamma) / \sigma (\gamma Z)$ and the helicity asymmetry in the $XX \rightarrow \gamma \gamma$ process, each as a function of mixing angle and $CP$-violating phase. As an application, we apply these results to searches for a class of MSSM models.