Sterile Neutrinos: Cosmology vs Short-BaseLine Experiments
  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.
