Baryogenesis from the Kobayashi-Maskawa Phase

Abstract

The smallness of quark masses suppresses the $CP$ violation from the Kobayashi-Maskawa phase to a level that is many orders of magnitude below what is required to explain the observed baryon asym­metry. We point out that if, as a result of time variation in the Yukawa couplings, quark masses were large at the time of the electroweak phase transition, then the Kobayashi-Maskawa mechanism could be the source of the asymmetry. The Froggatt-Nielsen mechanism provides a plausible framework where the Yukawa couplings could all be of order 1 at that time, and settle to their present values before nucleo­synthesis. The problems related to a strong first order electroweak phase transition may also be allevi­ated in this framework. Our scenario reveals a loophole in the commonly held view that the Kobayashi-Maskawa mechanism cannot be the dominant source of $CP$ violation to play a role in baryogenesis.