A Model For Late Dark Matter Decay
  The standard cold dark matter cosmological model, while successful in
explaining the observed large scale structure of the Universe, tends to
overpredict structure on small scales. It has been proposed this problem may be
alleviated in a class of late-decaying dark matter models, in which the parent
dark matter particle decays to an almost degenerate daughter, plus a
relativistic final state. We construct explicit particle physics models that
realize this goal while obeying observational constraints. To achieve this, we
introduce a pair of fermionic dark matter candidates and a new scalar field,
which obey either a Z4 or a U(1) symmetry. Through the spontaneous breaking of
these symmetries, and coupling of the new fields to standard model particles,
we demonstrate that the desired decay process may be obtained. We also discuss
the dark matter production processes in these models.
