If the dark matter is unstable , the decay of these particles throughout the universe and in the halo of the Milky Way could contribute significantly to the isotropic gamma-ray background ( IGRB ) as measured by Fermi .
In this article , we calculate the high-latitude gamma-ray flux resulting from dark matter decay for a wide range of channels and masses , including all contributions from inverse Compton scattering and accounting for the production and full evolution of cosmological electromagnetic cascades .
We also make use of recent multi-wavelength analyses that constrain the astrophysical contributions to the IGRB , enabling us to more strongly restrict the presence any component arising from decaying dark matter .
Over a wide range of decay channels and masses ( from GeV to EeV and above ) , we derive stringent lower limits on the dark matter ’ s lifetime , generally in the range of \tau \sim ( 1 - 5 ) \times 10 ^ { 28 } s .