Neutrino masses and cosmic radiation density: Combined analysis

Abstract

We determine the range of neutrino masses and cosmic radiation content allowed by the most recent CMB and large-scale structure data. In contrast to other recent works, we vary these parameters simultaneously and provide likelihood contours in the two-dimensional parameter space of N_eff}, the usual effective number of neutrino species measuring the radiation density, and \sum m_nu. The allowed range of \sum m_nu and N_eff has shrunk significantly compared to previous studies. The previous degeneracy between these parameters has disappeared, largely thanks to the baryon acoustic oscillation data. The likelihood contours differ significantly if \sum m_nu resides in a single species instead of the standard case of being equally distributed among all flavors. For \sum m_nu=0 we find 2.7 < N_eff < 4.6 at 95% CL while \sum m_nu < 0.62 eV at 95% CL for the standard radiation content.