Relic Neutrino Degeneracies and Their Impact on Cosmological Parameters. (arXiv:2010.01696v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Yeung_S/0/1/0/all/0/1">Shek Yeung</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lau_K/0/1/0/all/0/1">King Lau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chu_M/0/1/0/all/0/1">M.-C. Chu</a>
In the standard $Lambda$CDM 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 $xi$ using current cosmological data sets.
We find that $xi approx O(1)$ 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.
In the standard $Lambda$CDM 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 $xi$ using current cosmological data sets.
We find that $xi approx O(1)$ 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.
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