AAS 197, January 2001
Session 56. Frontiers of Astrophysics III
Joint Special Session Oral, Tuesday, January 9, 2001, 10:30am-12:00noon, Town and Country

[56.01] New Evidence for Neutrino Degeneracy in the Early Universe

G. Mathews (U. Notre Dame), T. Kajino, M. Orito (National Astronomical Observatory, Japan)

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 \nu\mu and \nu\tau degeneracies together with a moderate \nue degeneracy. We show that primordial nucleosynthesis by itself permits very large neutrino degeneracies 0. \le \xi_{\nu_{\mu}}, \xi_{\nu_{\tau}} \le 40, 0. \le \xi_{\nu_{e}} \le 1.4 together with large baryon densities 0.1 \le \Omegab h^{2}_{50} \le 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 \Omega = 1, \Omega\Lambda = 0.4, cosmological model for which there is both significant lepton asymetry (\vert \xi_{\nu_{\mu}} \vert = \vert \xi_{\nu_{\tau}} \vert \approx 11) and a relatively large baryon density (\Omegab \approx 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 \xi\nu_\mu = \xi\nu_\tau \approx 2, \xi\nu_e \approx 0.1, and \Omegab h502 \approx 0.1 for a broad range of cosmological parameters.