Inhomogeneous Neutrino Degeneracy and Big Bang Nucleosynthesis

Abstract

We examine Big Bang nucleosynthesis (BBN) in the case of inhomogenous neutrino degeneracy, in the limit where the fluctuations are sufficiently small on large length scales that the present-day element abundances are homogeneous. We consider two representive cases: degeneracy of the electron neutrino alone, and equal chemical potentials for all three neutrinos. We use a linear programming method to constrain an arbitrary distribution of the chemical potentials. For the current set of (highly-restrictive) limits on the primordial element abundances, homogeneous neutrino degeneracy barely changes the allowed range of the baryon-to-photon ratio. Inhomogeneous degeneracy allows for little change in the lower bound on the baryon-to-photon ratio, but the upper bound in this case can be as large as 1.1 \times 10^{-8} (only electron neutrino degeneracy) or 1.0 \times 10^{-9} (equal degeneracies for all three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show that there is no BBN upper bound on the neutrino energy density, which is bounded in this case only by limits from structure formation and the cosmic microwave background.

6 pages, no figures

References in corpus (2)

• The Small Observed Baryon Asymmetry from a Large Lepton Asymmetry
• Measuring the cosmological lepton asymmetry through the CMB anisotropy

Cited by in corpus (6)

• Primordial Nucleosynthesis: from precision cosmology to fundamental physics
• The cosmological baryon density from the deuterium to hydrogen ratio towards QSO absorption systems: D/H towards Q1243+3047
• Non equilibrium spectra of degenerate relic neutrinos
• Linear wave spectrum associated with collective neutrino-plasma interactions in the early universe
• Big Bang Nucleosynthesis with Gaussian Inhomogeneous Neutrino Degeneracy
• Does inhomogeneous big bang nucleosynthesis produce an inhomogeneous element distribution today?