Abstract
In the standard ΛCDM 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 ξ on the CMB angular power spectra, and obtain constraints on ξ using current cosmological data sets. We find that ξ≈ O(1) is still allowed. We also study the correlations between ξ, the Hubble parameter H 0, and the spectral index n s. Due to these correlations, the CMB constraints on inflation models are loosened when ξ is fitted together with other cosmological parameters, such that some models excluded at 95% confidence level by standard fittings without ξ could be revived. Furthermore, the tension in CMB and local measurements of H 0 is slightly alleviated. Our results suggest that ξ is a non-negligible physical parameter for cosmological analyses.
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