Cosmological bounds on active-sterile neutrino mixing after Planck data

Light sterile neutrinos can be produced by oscillations with active neutrinos in the early universe. Their properties can be constrained by their contribution as extra-radiation, parametrized in terms of the effective number of neutrino species N_eff, and to the universe energy density today Ω_vh². Both these parameters have been measured to quite a good precision by the Planck satellite experiment. We use these results to update the bounds on the parameter space of (3+1) sterile neutrino scenarios, with an active-sterile neutrino mass squared splitting in the range (10⁻⁵ — 10²)eV². For the first time we take into account the possibility of two non-vanishing active-sterile mixing angles. We find that the mass and mixing parameter space is severely constrained. In particular sterile neutrinos with m ∼ O(1) eV are strongly disfavoured by neutrino mass bound. (paper)