Gamma-rays from Light Dark Matter Decaying Through a Gravity Portal
Technical University of Munich & Max Planck Institute for Physics, Munich
One of the key properties of dark matter particles is their longevity. However, even if dark matter is absolutely stable against decay in flat spacetime, as commonly assumed in the literature, the presence of non-minimal couplings to gravity of the dark matter field can spoil this stability in curved spacetime, with potentially remarkable phenomenological implications. More specifically, a scalar dark matter candidate with a mass in the MeV-GeV range, destabilized through a linear coupling to the Ricci scalar, can decay into electron-positron pairs and photons. In this case, observations of the cosmic microwave background by the Planck satellite and of the extragalactic isotropic gamma-ray background by COMPTEL, EGRET and Fermi LAT can be used to constrain the size of the non-minimal coupling parameter.