Lepton asymmetry, neutrino spectral distortions, and big bang
  nucleosynthesis
  We calculate Boltzmann neutrino energy transport with self-consistently
coupled nuclear reactions through the weak-decoupling-nucleosynthesis epoch in
an early universe with significant lepton numbers. We find that the presence of
lepton asymmetry enhances processes which give rise to nonthermal neutrino
spectral distortions. Our results reveal how asymmetries in energy and entropy
density uniquely evolve for different transport processes and neutrino flavors.
The enhanced distortions in the neutrino spectra alter the expected big bang
nucleosynthesis light element abundance yields relative to those in the
standard Fermi-Dirac neutrino distribution cases. These yields, sensitive to
the shapes of the neutrino energy spectra, are also sensitive to the phasing of
the growth of distortions and entropy flow with time/scale factor. We analyze
these issues and speculate on new sensitivity limits of deuterium and helium to
lepton number.
