Initial State Radiation in Majorana Dark Matter Annihilations

TL;DR

This paper demonstrates that initial state radiation of gauge bosons can lift helicity suppression in Majorana dark matter annihilations, significantly affecting the expected signals in indirect detection experiments.

Contribution

It introduces a mechanism where initial state gauge boson emission enables s-wave annihilation of Majorana dark matter, altering the predicted energy spectra of Standard Model particles.

Findings

Initial state radiation lifts helicity suppression.

Enhanced s-wave annihilation cross section.

Altered energy spectra impact indirect detection.

Abstract

The cross section for a Majorana Dark Matter particle annihilating into light fermions is helicity suppressed. We show that, if the Dark Matter is the neutral Majorana component of a multiplet which is charged under the electroweak interactions of the Standard Model, the emission of gauge bosons from the initial state lifts the suppression and allows an s-wave annihilation. The resulting energy spectra of stable Standard Model particles are importantly affected. This has an impact on indirect searches for Dark Matter.