  We consider effective operators describing Dark Matter (DM) interactions with
Standard Model fermions. In the non-relativistic limit of the DM field, the
operators can be organized according to their mass dimension and their velocity
behaviour, i.e. whether they describe s- or p-wave annihilations. The analysis
is carried out for self-conjugate DM (real scalar or Majorana fermion). In this
case, the helicity suppression at work in the annihilation into fermions is
lifted by electroweak bremsstrahlung. We construct and study all dimension-8
operators encoding such an effect. These results are of interest in indirect DM
searches.
