  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.
