A Lifetime Bound for Decaying Dark Matter from the Isotropic Background, and Why It Is Conservative

Decaying dark matter would contribute a smooth, nearly isotropic gamma-ray component whose intensity is set by the particle's mass and lifetime. Inverting the published isotropic background intensity in a transparent, calibrated form, this paper derives a lower bound on the lifetime as a function of mass from ten GeV to ten TeV. It finds bound at 100GeV s = 1.000e+28; bound at 1TeV s = 3.981e+27. Because the Galactic decay signal, which is anisotropic and additional, is not used, the isotropic-only bound understates the full constraint, and the paper states that conservatism as part of the result. The study is simulated and computed, not measured.