Relic neutrino degeneracies and their impact on cosmological parameters

In the standard ACDM model, neutrinos are treated as radiation, with their masses and possible degeneracy ignored. In this paper, we compute the impact of a finite relic neutrino degeneracy xi on the CMB angular power spectra, and obtain constraints on using current cosmological data sets. We find that xi approximate to O(1) is still allowed. We also study the correlations between xi, the Hubble parameter H-0, and the spectral index n(s). Due to these correlations, the CMB constraints on inflation models are loosened when xi is fitted together with other cosmological parameters, such that some models excluded at 95% confidence level by standard fittings without xi could be revived. Furthermore, the tension in CMB and local measurements of H-0 is slightly alleviated. Our results suggest that xi is a non-negligible physical parameter for cosmological analyses.

Automated summary

This study investigates the impact of a finite relic neutrino degeneracy on the CMB angular power spectra and its correlations with other cosmological parameters. The results suggest that the relic neutrino degeneracy is a significant physical parameter for cosmological analyses, potentially loosening constraints on inflation models and slightly alleviating tensions in measurements.