Constraints on neutrino degeneracy from the cosmic microwave background and primordial nucleosynthesis

June 2002 • 2002PhRvD..65l3504O

Authors • Orito, M. • Kajino, T. • Mathews, G. J. • Wang, Y.

Abstract • 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 (Ω_bh²,ξ_νμ,τ,ξ_νe,Ω_Λ,h,n) plus the calibration uncertainties. We consider flat Ω_M+Ω_Λ=1 cosmological models with two identical degenerate neutrino species, ξ_νμ,τ≡\|ξ_νμ\|=\|ξ_ντ\| and a small ξ_νe. We assign weak top-hat priors on the electron-neutrino degeneracy parameter ξ_νe and Ω_bh² based upon allowed values consistent with the nucleosynthesis constraints as a function of ξ_νμ,τ. The change in the background neutrino temperature with degeneracy is also explicitly included, and Gaussian priors for h=0.72+/-0.08 and the experimental calibration uncertainties are adopted. The marginalized likelihood functions show a slight (0.5σ) preference for neutrino degeneracy. Optimum values with two equally degenerate μ and τ neutrinos imply ξ_νμ,τ=1.0^+0.8(1σ)_-1.0(0.5σ), from which we deduce ξ_νe=0.09^+0.15_-0.09, and Ω_bh²=0.021^+0.06_-0.002. The 2σ upper limit becomes ξ_νμ,τ<=2.1, which implies ξ_νe<=0.30, and Ω_bh²<=0.030. For only a single large-degeneracy species the optimal value is \|ξ_νμ\| or \|ξ_ντ\|=1.4 with a 2σ upper limit of \|ξ_νμ\| or \|ξ_ντ\|<=2.5.

Links

• PREPRINT http://arxiv.org/abs/astro-ph/0203352
• SPIRES http://inspirehep.net/search?p=find+j+PHRVA,D65,123504
• ELECTR http://link.aps.org/doi/10.1103/PhysRevD.65.123504
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0203352