The Shadow of Dark Matter

We carry out a model independent study of resonant photon scattering off dark matter (DM) particles. The DM particle chi_1 can feature an electric or magnetic transition dipole moment which couples it with photons and a heavier neutral particle chi_2. Resonant photon scattering then takes place at a special energy set by the masses of chi_1 and chi_2, with the width of the resonance set by the size of the transition dipole moment. We compute the constraints on the parameter space of the model from stellar energy losses, data from SN 1987A, the Lyman-alpha forest, Big Bang nucleosynthesis, electro-weak precision measurements and accelerator searches. We show that the velocity broadening of the resonance plays an essential role for the possibility of the detection of a spectral feature originating from resonant photon-DM scattering. Depending upon the particle setup and the DM surface mass density, the favored range of DM particle masses lies between tens of keV and a few MeV, while the resonant photon absorption energy is predicted to be between tens of keV and few GeV.