Likely Dominance of WIMP Annihilation to Fermion Pair + W/Z

TL;DR

This paper investigates how electroweak bremsstrahlung lifts helicity suppression in Majorana dark matter annihilation, leading to enhanced gauge boson radiation that impacts cosmic ray signatures and challenges existing models.

Contribution

It demonstrates that gauge boson radiation dominates Majorana DM annihilation, significantly affecting predicted cosmic ray signals and constraining model viability.

Findings

Radiation removes helicity suppression in Majorana DM annihilation.

Enhanced W/Z production leads to increased antiprotons.

Contrasts with positron observations challenge current models.

Abstract

Arguably, the most popular candidate for Dark Matter (DM) is a massive, stable, Majorana fermion. However, annihilation of Majorana DM to two fermions features a helicity-suppressed s-wave rate. The process radiating a gauge boson via electroweak (EW) and electromagnetic (EM) bremsstrahlung removes this s-wave suppression, and is likely to be the dominant modes of gauge-singlet Majorana DM annihilation. Given their enhanced annihilation rate with radiatedW and Z gauge bosons, and the subsequent dominant W/Z decays via hadronic channels, Majorana DM tends to produce more antiprotons than positrons. This result contrasts with observations, thereby presenting a challenge to model building with Majorana DM.