Isotropic diffuse gamma-ray background: unveiling Dark Matter components beyond the contribution of astrophysical sources

Abstract: We present the first interpretation of the new isotropic diffuse gamma-ray background (IGRB), measured by the Fermi Large Area Telescope (LAT), based on a statistical analysis. We demonstrate that the gamma-ray emission from unresolved active galactic nuclei and star forming galaxies is consistent with the Fermi-LAT IGRB data within the uncertainties both on the choice of the Galactic diffuse emission model and on the gamma-ray emission mechanism of these sources. Furthermore, adding to the extragalactic sources the contribution from a smooth Galactic halo of annihilating weakly interacting dark matter (DM) particles, we are able to set stringent limits on the DM annihilation cross section. Finally, we demonstrate that the addition of DM can significantly improve the fit to IGRB data.