Constraining Metastable Very Heavy Dark Matter using the Extragalactic Gamma-ray Background

We constrain the mass and lifetime of metastable very heavy dark matter particles (VHDM) using blazar emissions and the extragalactic gamma-ray background (EGB) as observed using the Fermi Gamma-ray Space Telescope. We calculate J factors along lines of sight and gamma-ray spectra from dark matter decay channels. Our results suggest that if VHDM particles contribute to the EGB, they must have lifetimes in excess of 10^25 seconds.