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.

在标准 ΛCDM 模型中，中微子被视为辐射，其质量和可能的简并性被忽略。在本文中，我们计算了有限遗迹中微子简并 ξ 对 CMB 角功率谱的影响，并使用当前宇宙学数据集获得对 ξ 的约束。我们发现 ξ≈ O(1) 仍然是允许的。我们还研究了 ξ、哈勃参数H ₀和光谱指数n _s之间的相关性。由于这些相关性，当 ξ 与其他宇宙学参数一起拟合时，CMB 对暴胀模型的约束会放宽，从而可以恢复一些被标准拟合排除在 95% 置信水平下而没有 ξ 的模型。此外，CMB 中的张力和H _{0 的}局部测量略有缓解。我们的结果表明 ξ 是宇宙学分析中不可忽略的物理参数。