Novel Spectral Features in MeV Gamma Rays from Dark Matter
  Astrophysical searches for gamma rays are one of the main strategies to probe the annihilation or decay of dark matter particles. We present a new class of distinct sub-GeV spectral features that generically appear in kinematical situations where the available center-of-mass energy in such processes is just above threshold to produce excited meson states. Using a Fisher forecast with realistic astrophysical backgrounds, we demonstrate that for upcoming experiments like e-ASTROGAM and ComPair these signals can turn out to be the smoking gun in the search for particle dark matter. 
Torsten Bringmann, Ahmad Galea, Andrzej Hryczuk and Christoph Weniger
hep-ph