Sterile Neutrinos: Cosmology vs Short-BaseLine Experiments

TL;DR

This paper analyzes the compatibility of light sterile neutrinos with cosmological and short baseline experimental data, finding consistent evidence for ~1 eV mass scale and partial thermalization scenarios.

Contribution

It provides a comprehensive combined analysis of cosmological and SBL data, considering partial thermalization, and identifies consistent sterile neutrino mass scales around 1 eV.

Findings

Preference for sterile neutrinos in both (3+1) and (3+2) scenarios.

Evidence at 3.3 sigma for (3+1) model with SBL data.

Mass scale around 1 eV for sterile neutrinos from combined data.

Abstract

Cosmology and short baseline 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 thermalised 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 3.3sigma 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 m_4 = (1.72 \pm 0.65) eV: this result is strenghtened by adding the prior from SBL posterior to m_4 = (1.27 \pm 0.12) eV (m_4 = (1.23 \pm 0.13) eV when SDSS is also considered in the cosmological analysis). In the (3+2) scheme, two additional, non--fully thermalized, neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of m_4 = (0.95 \pm 0.30) eV and m_5 = (1.59 \pm 0.49) eV. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, invoking a partial thermalisation the 3+1 model is still consistent with the latest data.