Refitting Cosmological Data with Neutrino Mass and Degeneracy

Abstract

A simple and natural extension of the standard Lambda cold dark matter (ΛCDM) model is to allow relic neutrinos to have finite chemical potentials. We confront this ΛCDM ξ model, a ΛCDM with neutrino mass M _ν and degeneracy ξ _3 as additional parameters, with various cosmological data sets. We find that the H _0 and S _8 tensions become significant only in the presence of the cosmic microwave background (CMB) polarization data. Specifically, the global and local measurements agree to within 0.8 σ and 1.6 σ for the H _0 and S _8 tensions, respectively, when the CMB polarization data are not included. Therefore, the H _0 and S _8 tensions exist between CMB temperature and polarization data, both being global measurements. Fitting the ΛCDM ξ model to the CMB temperature data, we find 3 σ evidence for nonzero neutrino mass ( ${M}_{\nu }=0.5{7}_{-0.13}^{+0.17}\,{{\rm{eV}}}$ ) and degeneracy ( ${\xi }_{3}=1.1{3}_{-0.19}^{+0.41}$ ), and the ${ \mathcal O }(1)$ neutrino degeneracy parameter is compatible with Big Bang nucleosynthesis data. The scalar index n _s exceeds 1 slightly, which is compatible with some hybrid inflation models. Furthermore, the recent DESI baryon acoustic oscillation data prefer the ΛCDM ξ model to the Planck ΛCDM model. Similar results are obtained when including additional supernova data, while the inclusion of the Atacama Cosmology Telescope τ prior shifts the preferred M _ν and ξ _3 values closer to zero and brings n _s back to the values favored when the polarization data are included.

Keywords

• Cosmic microwave background radiation
• Cosmological parameters
• Cosmological neutrinos