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The South Pole Telescope (SPT), Atacama Cosmology Telescope (ACT), andWilkinson Microwave Anisotropy Probe (WMAP) have each reported measurements ofthe cosmic microwave background's (CMB) angular power spectrum which favor theexistence of roughly one additional neutrino species, in addition to the threecontained in the standard model of particle physics. Neutrinos influence theCMB by contributing to the radiation density, which alters the expansion rateof the universe during the epoch leading up to recombination. In this paper, weconsider an alternative possibility that the excess kinetic energy implied bythese measurements was possessed by dark matter particles that were producedthrough a non-thermal mechanism, such as late-time decays. In particular, wefind that if a small fraction (<1%) of the dark matter in the universe todaywere produced through the decays of a heavy and relatively long-lived state,the expansion history of the universe can be indistinguishable from thatpredicted in the standard cosmological model with an additional neutrino.Furthermore, if these decays take place after the completion of big bangnucleosynthesis, this scenario can avoid tension with the value of threeneutrino species preferred by measurements of the light element abundances.

Non-Thermal Dark Matter Mimicking An Additional Neutrino Species In The Early Universe