Initial State Radiation in Majorana Dark Matter Annihilations
  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. 
Paolo Ciafaloni, Marco Cirelli, Denis Comelli, Andrea De Simone,   Antonio Riotto, Alfredo Urbano
hep-ph