Effective Theory of Dark Matter Decay into Monochromatic Photons and its
  Implications: Constraints from Associated Cosmic-Ray Emission
  We show that there exists only a quite limited number of higher dimensional
operators which can naturally lead to a slow decay of dark matter particles
into monochromatic photons. As each of these operators inevitably induces
decays into particles other than photons, we show that the gamma-lines it
induces are always accompanied by a continuum flux of cosmic rays. Hence
constraints on cosmic-ray fluxes imply constraints on the intensity of
gamma-lines and vice-versa. A comparison with up to date observational bounds
shows the possibilities to observe or exclude cosmic rays associated to
gamma-line emission, so that one could better determine the properties of the
DM particle, possibly discriminating between some of the operators.
