ABSENCE OF A LOWER LIMIT ON Ωb IN INHOMOGENEOUS PRIMORDIAL NUCLEOSYNTHESIS

We show that a class of inhomogeneous big bang nucleosynthesis models exist which yield light-element abundances in agreement with observational constraints for baryon-tophoton ratios significantly smaller than those inferred from standard homogeneous big bang nucleosynthesis (HBBN). These inhomogeneous nucleosynthesis models are characterized by a bimodal distribution of baryons in which some regions have a local baryon-to-photon ratio η ≈ 3×10, while the remaining regions are baryon-depleted. HBBN scenarios with primordial (H+ He)/H ∼ 9 × 10 −5 necessarily require that most baryons be in a dark or non-luminous form, although new observations of a possible high deuterium abundance in Lyman-α clouds may relax this requirement somewhat. The models described here present another way to relax this requirement and can even eliminate any lower bound on the baryon-to-photon ratio. Subject headings: early universe abundances, nuclear reactions, nucleosynthesis, cosmology dark matter