Constraints on dark matter annihilation to fermions and a photon
  We consider Majorana dark matter annihilation to fermion - anti-fermion pair
and a photon in the effective field theory paradigm, by introducing dimension 6
and dimension 8 operators in the Lagrangian. For a given value of the cut-off
scale, the latter dominates the annihilation process for heavier dark matter
masses. We find a cancellation in the dark matter annihilation to a fermion -
anti-fermion pair when considering the interference of the dimension 6 and the
dimension 8 operators. Constraints on the effective scale cut-off is derived
while considering indirect detection experiments and the relic density
requirements and they are compared to the bound coming from collider
experiments.
