Probing the properties of relic neutrinos using the cosmic microwave background, the Hubble Space Telescope and galaxy clusters

Abstract We investigate the observational constraints on the cosmic neutrino background (CNB) given by the extended ΛCDM scenario (ΛCDM $+ N_{\rm eff} + \sum m_{\nu } + c^2_{\rm eff} + c^2_{\rm vis} + \xi _{\nu }$) using the latest observational data from the cosmic microwave background (CMB) as observed by Planck (i.e. temperature power spectrum, low-polarization and lensing reconstruction), baryon acoustic oscillations (BAOs), the new recent local value of the Hubble constant from the Hubble Space Telescope (HST) and information on the abundance of galaxy clusters (GCs). We study the constraints on the CNB background using CMB + BAO + HST data with and without the GC data. We find ΔNeff = 0.614 ± 0.26 at the 68 per cent confidence level when the GC data are added to the analysis. We do not find any significant deviation for sound speed in the CNB rest frame. We also analyse the particular case ΛCDM +Neff + ∑mν + ξν with the observational data. Within this scenario, we find ΔNeff = 0.60 ± 0.28 at the 68 per cent confidence level. In both scenarios, no mean deviations are found for the degeneracy parameter.