CONSTRAINTS ON BARYOGENESIS FROM THE DECAY OF SUPERSTRING AXIONS

We calculate the dilution of the baryon-to-photon ratio by the decay o f superstring axions, We find that the dilution is of the order of 10( 7). We review several models of baryogenesis and show that most of the m can not tolerate such a large dilution, In particular, only one curr ent model of electroweak baryogenesis possibly survives. The Affleck-D ine mechanism in SUSY GUTs is very robust and the dilution by axions c ould contribute to the dilution required in these models. Baryogenesis scenarios involving topological defects and black hole evaporation ar e also capable of producing a sufficiently large baryon asymmetry.