Geometrical effects of baryon density inhomogeneities on primordial nucleosynthesis

We discuss effects of fluctuation geometry on primordial nucleosynthesis. For the first time we consider condensed cylinder and cylindrical-shell fluctuation geometries in addition to condensed spheres and spherical shells. We find that a cylindrical shell geometry might allow for an appreciably higher baryonic fraction of the closure density (Ω_bh₅₀² ≲ 0.2) than that allowed in spherical inhomogeneous or standard homogeneous big bang models. This result, which is contrary to those of some other recent studies, is due to both geometry and recently revised estimates of the uncertainties in the observationally inferred primordial light-element abundances. We also find that inhomogeneous primordial nucleo-synthesis in the cylindrical shell geometry can lead to significant Be and B production. In particular, this geometry produces a primordial beryllium abundance as high as [Be] = 12 + log (Be/H) ≈ -3 while still satisfying all of the light-element abundance constraints.