Neutrino masses and cosmic radiation density: Combined analysis
Steen Hannestad, Georg G. Raffelt
TL;DR
The paper tackles joint constraints on the total neutrino mass $\sum m_\nu$ and the cosmic radiation density $N_{\rm eff}$ using the latest CMB and large-scale-structure data. It performs a likelihood analysis with $\sum m_\nu$ and $N_{\rm eff}$ treated as free parameters, exploring three neutrino-mass-distribution scenarios, and excludes Lyman-$\alpha$ data. A major finding is that BAO data remove the prior degeneracy between $\sum m_\nu$ and $N_{\rm eff}$, yielding robust 95% CL bounds: $2.7 < N_{\rm eff} < 4.6$ and $\sum m_\nu<0.62$ eV for the standard case; the LSND 3+1 scenario tightens to $\sum m_\nu<0.45$ eV. Overall, the results show near-independence of the two parameters and that current cosmological data are consistent with the standard neutrino sector, while allowing limited room for nonstandard radiation.
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.