Resolving Cosmic Gamma Ray Anomalies with Dark Matter Decaying Now

Dark matter particles need not be completely stable, and in fact they may be decaying now. We consider this possibility in the frameworks of universal extra dimensions and supersymmetry with very late decays of weakly interacting massive particles to Kaluza-Klein gravitons and gravitinos. The diffuse photon background is a sensitive probe, even for lifetimes far greater than the age of the Universe. Remarkably, both the energy spectrum and flux of the observed MeV γ-ray excess may be simultaneously explained by decaying dark matter with MeV mass splittings. Future observations of continuum and line photon fluxes will test this explanation and may provide novel constraints on cosmological parameters.