Candidates for a hypercharge axion in extensions of the standard model

Many theoretically well-motivated extensions of the standard model contain heavy pseudoscalars that couple to hypercharge topological density. The cosmological dynamics of such hypercharge axions could, under certain conditions, lead to the generation of a net baryon number in a sufficient amount to explain the observed baryon asymmetry in the universe. We examine the minimal supersymmetric standard model and string or M-theory models and determine specific conditions which heavy axion-like pseudoscalars must satisfy to successfully drive baryogenesis. We find that all candidates in the minimal supersymmetric standard model fail to obey some of the constraints, and that only in special string or M-theory models may some axions be adequate.