Inhomogeneous Big Bang Nucleosynthesis: Upper Limit on Omega_b and Production of Lithium, Beryllium, and Boron

Abstract

We examine the Big Bang nucleosynthesis (BBN) process in the presence of small-scale baryon inhomogeneities. Primordial abundance yields for D, He4, Li6, Li7, Be9, and B11 are computed for wide ranges of parameters characterizing the inhomogeneities taking account of all relevant diffusive and hydrodynamic processes. These calculations may be of interest due to (a) recent observations of the anisotropies in the cosmic microwave background radiation favoring slightly larger baryonic contribution to the critical density, Omega_b, than allowed by a standard BBN scenario and (b) new observational determinations of Li6 and Be9 in metal-poor halo stars. We find considerable parameter space in which production of D and He4 is in agreement with observational constraints even for Omega_b h^2 a factor 2-3 larger than the Omega_b inferred from standard BBN. Nevertheless, in this parameter space synthesis of Li7 in excess of the inferred Li7 abundance on the Spite plateau results. Production of Li6, Be9, and B11 in inhomogeneous BBN scenarios is still typically well below the abundance of these isotopes observed in the most metal-poor stars to date thus neither confirming nor rejecting inhomogeneous BBN. In an appendix we summarize results of a reevaluation of baryon diffusion constants entering inhomogeneous BBN calculations.