First-order electroweak phase transition from weakly coupled sub-GeV physics and possible connection to fermion flavor

We propose that the dynamics of a scalar phi of mass O(10) MeV that is weakly coupled to the Higgs can lead to a first-order electroweak phase transition, fulfilling a key requirement for baryogenesis. The stability of the model near the weak scale requires a suppressed-possibly vanishing-top Yulcawa coupling to the Higgs before the transition which rises to the Standard Model value afterwards. This can be accomplished through the dynamics of phi via a dimension-five operator. We conjecture that the entire Standard Model flavor structure could turn on, mutatis mutandis, after the electroweak phase transition, via dimension-five interactions of phi suppressed by scales ranging from O(10(3)) TeV to near the Planck mass. Due to its suppressed couplings, phi is long lived and can lead to missing energy signals in rare kwon decays, which can be probed by the KOTO experiment.