Non-Thermal Dark Matter Mimicking An Additional Neutrino Species In The
  Early Universe
  The South Pole Telescope (SPT), Atacama Cosmology Telescope (ACT), and
Wilkinson Microwave Anisotropy Probe (WMAP) have each reported measurements of
the cosmic microwave background's (CMB) angular power spectrum which favor the
existence of roughly one additional neutrino species, in addition to the three
contained in the standard model of particle physics. Neutrinos influence the
CMB by contributing to the radiation density, which alters the expansion rate
of the universe during the epoch leading up to recombination. In this paper, we
consider an alternative possibility that the excess kinetic energy implied by
these measurements was possessed by dark matter particles that were produced
through a non-thermal mechanism, such as late-time decays. In particular, we
find that if a small fraction (<1%) of the dark matter in the universe today
were produced through the decays of a heavy and relatively long-lived state,
the expansion history of the universe can be indistinguishable from that
predicted in the standard cosmological model with an additional neutrino.
Furthermore, if these decays take place after the completion of big bang
nucleosynthesis, this scenario can avoid tension with the value of three
neutrino species preferred by measurements of the light element abundances.
