Bremsstrahlung and Gamma Ray Lines in 3 Scenarios of Dark Matter Annihilation

TL;DR

This paper compares gamma ray spectral signatures from three dark matter annihilation scenarios, highlighting their differences and providing new calculations for scalar DM annihilation into two gamma rays, aiding indirect detection efforts.

Contribution

It introduces a new calculation for scalar dark matter annihilation into two gamma rays and compares spectral signatures across three dark matter models.

Findings

Distinct gamma ray spectral signatures for each scenario.

Scalar DM annihilation into two gammas has a unique amplitude calculation.

Phenomenological differences help distinguish dark matter models.

Abstract

Gamma ray spectral features are of interest for indirect searches of dark matter (DM). Following Barger et al, we consider 3 simple scenarios of DM that annihilates into Standard Model (SM) fermion pairs. Scenario 1 is a Majorana DM candidate coupled to a charged scalar, scenario 2 is a Majorana DM coupled to a charged gauge boson and scenario 3 is a real scalar DM coupled a charged vector-like fermion. As shown by Barger et al, these 3 scenarios share precisely the same internal Bremsstrahlung spectral signature into gamma rays. Their phenomenology is however distinct. In particular for annihilation into light SM fermions, in the chiral limit, the 2-body annihilation cross section is p-wave suppressed for the Majorana candidates while it is d-wave suppressed for the real scalar. In the present work we study the annihilation into 2 gammas, showing that these three scenarios have distinct, and so potentially distinguishable, spectral signatures into gamma rays. In the case of the real scalar candidate we provide a new calculation of the amplitude for annihilation into 2 gammas.