Dark Radiation or Warm Dark Matter from long lived particle decays in the light of Planck

Although Planck data supports the standard ACDM model, it still allows for the presence of Dark Radiation corresponding up to about half an extra standard neutrino species. We propose a scenario for obtaining a fractional effective neutrino species from a thermally produced particle which decays into a much lighter stable relic plus standard fermions. At lifetimes much longer than similar to 1 s, both the relic particles and the non-thermal neutrino component contribute to Dark Radiation. By increasing the stableto-unstable particle mass ratio, the relic particle no longer acts as Dark Radiation but instead becomes a candidate for Warm Dark Matter with mass O(1 keV-100 GeV). In both cases it is possible to address the lithium problem. (C) 2013 Elsevier B.V. All rights reserved.