Constraints on dark radiation from cosmological probes
  We present joint constraints on the number of effective neutrino species
N_eff and the sum of neutrino masses M_nu, based on a technique which exploits
the full information contained in the one-dimensional Lyman-Alpha forest flux
power spectrum, complemented by additional cosmological probes. In particular,
we obtain N_eff=2.91(+0.21)(-0.22) (95% CL) and M_nu<0.15 eV (95% CL) when we
combine BOSS Lyman-Alpha forest data with CMB (Planck+ACT+SPT+WMAP
polarization) measurements, and N_eff=2.88(+0.20)(-0.20) (95% CL) and M_nu<0.14
eV (95% CL) when we further add baryon acoustic oscillations. Our results
provide evidence for the Cosmic Neutrino Background from N_eff~3 (N_eff=0 is
rejected at more than 14 sigma), and rule out the possibility of a sterile
neutrino thermalized with active neutrinos (i.e., N_eff=4) - or more generally
any decoupled relativistic relic with Delta N_eff ~ 1 - at a significance of
over 5 sigma, the strongest bound to date, implying that there is no need for
exotic neutrino physics in the concordance LCDM model.
