  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 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/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/M-theory models some axions may be adequate.
