Dark radiation sterile neutrino candidates after Planck data

Abstract

Recent Cosmic Microwave Background (CMB) results from the Plancksatellite, combined with previous CMB data and Hubble constantmeasurements from the Hubble Space Telescope, provide a constraint on theeffective number of relativistic degrees of freedom 3.62+0.50−0.48 at 95% CL. New Planck data provide a unique opportunity to place limitson models containing relativistic species at the decouplingepoch. We present here the bounds on sterile neutrino models combiningPlanck data with galaxy clustering information. Assuming Neff active plus sterile massive neutrinospecies, in the case of a Planck+WP+HighL+HST analysis we find mν, sterileeff < 0.36 eV and 3.14 < Neff < 4.15 at95% CL, while using Planck+WP+HighL data in combination with the fullshape of the galaxy power spectrum from the Baryon Oscillation Spectroscopic Survey BOSS DataRelase 9 measurements, we find that 3.30 < Neff < 4.43 and mν, sterileeff < 0.33 eV both at95% CL with the three active neutrinos having the minimummass allowed in the normal hierarchy scheme, i.e. ∑mν ∼ 0.06 eV. These values compromise the viability of the (3+2) massive sterile neutrinomodels for the parameter region indicated by global fits of neutrinooscillation data. Within the (3+1) massive sterile neutrino scenario, we find mν, sterileeff < 0.34 eV at95% CL. While the existence of one extra sterile massive neutrino state iscompatible with current oscillation data, the values for thesterile neutrino mass preferred by oscillation analyses are significantlyhigher than the current cosmological bound. We review as well the bounds on extended dark sectors with additional light species based on the latest Planck CMB observations.