Sterile neutrinos: Cosmology versus short-baseline experiments

Abstract

Cosmology and short-baseline (SBL) neutrino oscillation data both hint at the existence of light sterile neutrinos with masses in the 1 eV range. Here we perform a detailed analysis of the sterile neutrino scenario using both cosmological and SBL data. We have additionally considered the possibility that the extra neutrino degrees of freedom are not fully thermalized in the early universe. Even when analyzing only cosmological data we find a preference for the existence of massive sterile neutrinos in both (3+1) and (3+2) scenarios, and with the inclusion of SBL data the evidence is formally at the 3.3σ level in the case of a (3+1) model. Interestingly, cosmological and SBL data both point to the same mass scale of approximately 1 eV. In the (3+1) framework WMAP9+SPT provide a value of the sterile mass eigenstate m₄=(1.72±0.65)eV; this result is strengthened by adding the prior from SBL posterior to m₄=(1.27±0.12)eV [m₄=(1.23±0.13)eV when data from the Sloan Digital Sky Survey is also considered in the cosmological analysis]. In the (3+2) scheme, two additional, nonfully thermalized neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of m₄=(0.95±0.30)eV and m₅=(1.59±0.49)eV. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, by invoking a partial thermalization the 3+1 model is still consistent with the latest data.