Light sterile neutrinos after BICEP-2
  The recent discovery of B-modes in the polarization pattern of the Cosmic
Microwave Background by the BICEP2 experiment has important implications for
neutrino physics. We revisit cosmological bounds on light sterile neutrinos and
show that they are compatible with all current cosmological data provided that
the mass is relatively low. Using CMB data, including BICEP-2, we find an upper
bound of $m_s < 0.85$ eV ($2\sigma$ Confidence Level). This bound is
strengthened to 0.48 eV when HST measurements of $H_0$ are included. However,
the inclusion of SZ cluster data from the Planck mission and weak gravitational
measurements from the CFHTLenS project favours a non-zero sterile neutrino mass
of $0.44^{+0.11}_{-0.16}$ eV. Short baseline neutrino oscillations, on the
other hand, indicate a new mass state around 1.2 eV. This mass is highly
incompatible with cosmological data if the sterile neutrino is fully
thermalised ($\Delta \chi^2>10$). However, if the sterile neutrino only partly
thermalises it can be compatible with all current data, both cosmological and
terrestrial.
