Lepton asymmetry, neutrino spectral distortions, and big bang nucleosynthesis

TL;DR

This paper models neutrino energy transport and nuclear reactions during the early universe, showing how lepton asymmetry causes spectral distortions that impact big bang nucleosynthesis yields.

Contribution

It introduces a self-consistent calculation of neutrino spectral distortions with lepton asymmetry, revealing their effects on element formation in the early universe.

Findings

Lepton asymmetry enhances neutrino spectral distortions.

Spectral distortions influence light element abundances.

Different neutrino flavors and energy/entropy densities evolve uniquely.

Abstract

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.