New Evidence for Neutrino Degeneracy in the Early Universe

Details New Evidence for Neutrino Degeneracy in the Early Universe New Evidence for Neutrino Degeneracy in the Early Universe

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...197.5601m&link_type=abstract

American Astronomical Society, 197th AAS Meeting, #56.01; Bulletin of the American Astronomical Society, Vol. 32, p.1497

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We reanalyze cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy in light of reanalyzed primordial nucleosynthesis and the recently reported CMB power spectra from BOOMERANG and MAXIMA-1. We explore physically plausible lepton-asymmetric models with large ν μ and ν τ degeneracies together with a moderate ν e degeneracy. We show that primordial nucleosynthesis by itself permits very large neutrino degeneracies 0. <= ξν_μ, ξν_τ <= 40, 0. <= ξνe <= 1.4 together with large baryon densities 0.1 <= Ω b h250 <= 1 as long as some destruction of primordial lithium is assumed. We also show that structure formation and the power spectrum of the cosmic microwave background allows for the possibility of an Ω = 1, Ω Λ = 0.4, cosmological model for which there is both significant lepton asymetry (| ξν_μ | = | ξν_τ | ≈ 11) and a relatively large baryon density (Ω b ≈ 0.06). The best neutrino asymmetric models naturally accommodate the observed suppression of the second acoustic peak in the CMB spectrum. Goodness of fit contours show a well developed minimum with degeneracy parameter ξ ν μ = ξ ν τ ≈ 2, ξ ν e ≈ 0.1, and Ω b h502 ≈ 0.1 for a broad range of cosmological parameters.

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