Dark radiation and small-scale structure problems with decaying
  particles
  Although the standard {\Lambda}CDM model describes the cosmic microwave
background radiation and the large scale structure of the Universe with great
success, it has some tensions with observations in the effective number of
neutrino species (dark radiation) and the number of small scale structures
(overabundance problem). Here we propose a scenario which can relax these
tensions by producing both dark matter and dark radiation by late decays of
heavy particle. Thanks to the generation mechanism, dark matters are rather
warm so that the small-scale structure problem is resolved. This scenario can
be naturally realized in supersymmetric axion model, in which axions produced
by saxion decays provide dark radiation, while axinos from saxion decays form
warm dark matter. We identify a parameter region of supersymmetric axion model
satisfying all known cosmological constraints.
