Model-independent dark matter annihilation bound from the diffuse gamma ray flux
M. Kachelriess, P. D. Serpico
TL;DR
The paper develops a model-independent bound on the dark matter annihilation cross section by comparing predicted gamma-ray flux from DM annihilation to the observed diffuse gamma-ray background. It shows that electroweak bremsstrahlung yields electromagnetic final states even for neutrino-only couplings, making gamma-ray bounds competitive with neutrino-based bounds at TeV masses. By focusing on the Galactic halo's smooth DM distribution and using an NFW profile, the authors derive a conservative bound based on EGRET data, with the potential for improvement from GLAST. They also argue that the strongest and most robust constraint comes from the Galactic halo signal, and discuss how angular information and halo substructure could tighten the bounds.
Abstract
An upper limit on the total annihilation cross section of dark matter (DM) has recently been derived from the observed atmospheric neutrino background. We show that comparable bounds are obtained for DM masses around the TeV scale by observations of the diffuse gamma-ray flux by EGRET, because electroweak bremsstrahlung leads to non-negligible electromagnetic branching ratios, even if DM particles only couple to neutrinos at tree level. A better mapping and the partial resolution of the diffuse gamma-ray background into astrophysical sources by the GLAST satellite will improve this bound in the near future.