Novel gamma-ray features from dark matter cascade processes involving scalars and fermions as intermediate states

We present novel gamma-ray features that are almost exclusively a consequence of kinematical considerations in one-step cascade processes. These features arise from relativistic effects on final state photons from decaying intermediate states. Depending on the spin of the intermediate state the specific shape of the signal varies: a scalar or Majorana fermion intermediate state produces gamma-ray boxes, whereas a Dirac fermion intermediate state produces gamma-ray triangles. We refer to physical realisations that produce such features. Finally, we illustrate their strong constraining power using data drawn from the Fermi-LAT instrument. (paper)