Candidates for a hypercharge axion in extensions of the standard model - art. no. 055002

Many theoretically well-motivated extensions of the standard model contain heavy pseucloscalars that couple to hypercharge topological density. The co smological dynamics of such hypercharge axions could, under certain conditi ons, lead to the generation of a net baryon number in a sufficient amount t o explain the observed baryon asymmetry in the universe. We examine the min imal supersymmetric. standard model and string or M-theory models and deter mine specific conditions which heavy axion-like pseudoscalars must satisfy to successfully drive baryogenesis. We find that all candidates in the mini mal 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 .