Constraints on Neutrino Degeneracy from the Cosmic Microwave Background and Primordial Nucleosynthesis

Details Constraints on Neutrino Degeneracy from the Cosmic Microwave Background and Primordial Nucleosynthesis Constraints on Neutrino Degeneracy from the Cosmic Microwave Background and Primordial Nucleosynthesis

2002-03-20

arxiv.org/abs/astro-ph/0203352v1

Phys.Rev. D65 (2002) 123504

Astronomy and Astrophysics

Astrophysics

8 pages, 5 figures, Phys. Rev. D. Submitted

Scientific paper

10.1103/PhysRevD.65.123504

We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy based upon the latest high resolution CMB sky maps from BOOMERANG, DASI, and MAXIMA-1. We generate likelihood functions by marginalizing over $(\omegab h^2,\xinumt, \xinue, \Omega_\Lambda,h,n)$ plus the calibaration uncertainties. We consider flat $\Omega_M + \Omega_\Lambda = 1$ cosmological models with two identical degenerate neutrino species, $\xinumt \equiv \vert \xinum \vert = \vert \xinut \vert$ and a small $\xinue$. We assign weak top-hat priors on the electron-neutrino degeneracy parameter $\xinue$ and $\Omega_b h^2$ based upon allowed values consistent with the nucleosynthesis constraints as a function of $\xinumt$. The change in the background neutrino temperature with degeneracy is also explicitly included, and Gaussian priors for $h = 0.72 \pm 0.08$ and the experimental calibration uncertainties are adopted. The marginalized likelihood functions show a slight (0.5$\sigma$) preference for neutrino degeneracy. Optimum values with two equally degenerate $\mu$ and $\tau$ neutrinos imply $\xinumt = 1.0^{+0.8 (1\sigma)}_{-1.0 (0.5\sigma)}$, from which we deduce $\xi_{\nu_e} = 0.09^{+0.15}_{-0.09}$, and $\Omega_b h^2 = 0.021^{+0.06}_{- 0.002}$. The $2\sigma$ upper limit becomes $ \xinumt \le 2.1$, which implies $\xi_{\nu_e} \le 0.30$, and $\Omega_b h^2 \le 0.030$. For only a single large-degeneracy species the optimal value is $\vert \xinum \vert$ or $\vert \xinut \vert = 1.4$ with a $2\sigma$ upper limit of $\vert \xinum \vert$ or $\vert \xinut \vert \le 2.5$

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