Constraints on massive unstable dark matter from ultrahigh-energy γ-ray flux

Abstract

We ruled out regions in parameter space of the mass, lifetime and branching ratio for radiative decay of massive unstable dark matter particles based on upper limits to the ultrahigh-energy cosmic diffuse γ-ray spectrum. The lifetime of massive unstable particles is shown to be no shorter than ∼ 1017 s if they exist at a density equal to the cosmological critical density. The branching ratio for radiative decay of such massive unstable particles is less than 10-11 at mass of 1 GeV and 10-2 at 105 GeV.