Constraining Dark-Matter Ensembles with Supernova Data
  The constraints on non-minimal dark sectors involving ensembles of unstable
dark-matter species are well established and quite stringent in cases in which
these species decay to visible-sector particles. However, in cases in which
these ensembles decay exclusively to other, lighter dark-sector states, the
corresponding constraints are less well established. In this paper, we
investigate how information about the expansion rate of the universe at low
redshifts gleaned from observations of Type Ia supernovae can be used to
constrain ensembles of unstable particles which decay primarily into dark
radiation.
