Constraints on massive sterile neutrino species from current and future
  cosmological data
  Sterile massive neutrinos are a natural extension of the Standard Model of
elementary particles. The energy density of the extra sterile massive states
affects cosmological measurements in an analogous way to that of active
neutrino species. We perform here an analysis of current cosmological data and
derive bounds on the masses of the active and the sterile neutrino states as
well as on the number of sterile states. The so-called (3+2) models with three
sub-eV active massive neutrinos plus two sub-eV massive sterile species is well
within the 95% CL allowed regions when considering cosmological data only. If
the two extra sterile states have thermal abundances at decoupling, Big Bang
Nucleosynthesis bounds compromise the viability of (3+2) models. Forecasts from
future cosmological data on the active and sterile neutrino parameters are also
presented. Independent measurements of the neutrino mass from tritium beta
decay experiments and of the Hubble constant could shed light on sub-eV massive
sterile neutrino scenarios.
