Big bang nucleosynthesis and the quark-hadron transition

An examination and a brief review are made of the effects of quark-hadron transition induced fluctuations on big bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogenous calculations might be loosened by as much as 50%, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N_v ≲ 4. To achieve baryon densities ≲0.3 of critical density would require initial density contrasts R ≫ 10³, whereas the simplest models for the transition seem to restrict R to ≲ 10².