Abstract
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 gamma-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.
Highlights
Dark matter particles need not be completely stable, and they may be decaying. 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 abundance of dark matter is well known from observations of supernovae, galaxies and galactic clusters, and the cosmic microwave background (CMB) [1], but its identity remains elusive
In this Letter, we study the contribution to the cosmic gamma ray background (CGB) from dark matter decaying
Summary
Both the energy spectrum and flux of the observed MeV -ray excess may be simultaneously explained by decaying dark matter with MeV mass splittings. In supersymmetry (SUSY) and other widely studied scenarios, it is just as natural for WIMPs to decay after freeze-out to other stable particles with similar masses, which automatically inherit the right relic density to be dark matter [3].
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