Conservative upper limits on WIMP annihilation cross section from Fermi-LAT γ-rays

Abstract

The spectrum of an isotropic extragalactic γ-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subtraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain conservative upper limits on their annihilation cross section 〈σν〉. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, would 〈σν〉 be inversely proportional to the WIMP velocity, very severe limits are derived for the velocity-independent term of the annihilation cross section.