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 Z(4) 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.