Fermi-lat limits on mass degenerate dark matter scenarios

We analyze scenarios where the dark matter is constituted by Majorana fermions which interact via a Yukawa coupling with a Standard Model fermion and a scalar. In this class of scenarios, the higher order annihilation process into a fermion-antifermion pair with the associated emission of a photon can have a sizable cross section and even be the dominant annihilation channel. Futhermore, the energy spectrum of photons presents a sharp feature towards the endpoint of the spectrum that resembles a distorted line. We have searched in the Fermi-LAT data for the gamma-ray produced in this process and we have set stringent limits on the annihilation cross section which are a factor of a few above the expected value for a thermal relic. In fact, we already find a weak indication, with a significance of 3.1σ (4.3σ) when (not) taking into account the look-elsewhere effect, for a signal that would correspond to a dark matter mass of ~ 150 GeV. We also discuss the constraints on this class of scenarios from antiproton limits and direct search experiments.