Inhomogeneous big bang nucleosynthesis: Upper limit on Ωb and production of lithium, beryllium, and boron

We examine the big bang nucleosynthesis (BBN) process in the presence of small-scale baryon inhomogeneities. Primordial abundance yields for D, ⁴He, ⁶Li, ⁷Li, ⁹Be, and ¹¹B 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, Ω_b, than allowed by a standard BBN scenario and (b) new observational determinations of ⁶Li and ⁹Be in metal-poor halo stars. We find considerable parameter space in which production of D and ⁴He is in agreement with observational constraints even for Ω_bh² a factor 2 or 3 larger than the Ω_b inferred from standard BBN. Nevertheless, in this parameter space synthesis of ⁷Li in excess of the inferred ⁷Li abundance on the Spite plateau results. Production of ⁶Li, ⁹Be, and ¹¹B 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.