Abstract
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. Stability of the model near the weak scale requires a suppressed - possibly vanishing - top Yukawa 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-5 operator. We conjecture that the entire Standard Model flavor structure could turn on, mutatis mutandis, after the electroweak phase transition, via dimension-5 interactions of $\phi$ suppressed by scales ranging from $O(10^3)$ TeV to near Planck mass. Due to its suppressed couplings, $\phi$ is long-lived and can lead to missing energy signals in rare kaon decays, which can be probed by the KOTO experiment.
Highlights
It is widely accepted that the Standard Model (SM) does not contain sufficient ingredients to generate the observed baryon asymmetry of the Universe (BAU) [1]
Another class of solutions for achieving a first-order phase transition (FOPT) entails the addition of higher-dimension operators ðH†HÞn, with integer n > 2. Such interactions would allow deviations from the SM value of λH in order to satisfy the condition (1) and obtain a first-order transition [23,24]. In this class of models, it is generally required that the higher-dimension operators are suppressed by scales Λ ∼ 1 TeV, which implies the presence of new physics not far above mH
We propose an alternative approach to generating an electroweak FOPT, where a light new scalar φ, with suppressed couplings to the Higgs boson and other SM particles, appears at energies well below the weak scale
Summary
It is widely accepted that the Standard Model (SM) does not contain sufficient ingredients to generate the observed baryon asymmetry of the Universe (BAU) [1]. Such interactions would allow deviations from the SM value of λH in order to satisfy the condition (1) and obtain a first-order transition [23,24] In this class of models, it is generally required that the higher-dimension operators are suppressed by scales Λ ∼ 1 TeV, which implies the presence of new physics not far above mH. We propose an alternative approach to generating an electroweak FOPT, where a light new scalar φ, with suppressed couplings to the Higgs boson and other SM particles, appears at energies well below the weak scale. The only other field that we explicitly introduce is a scalar with a mass ∼10 TeV after the transition and a small coupling to φ, which is largely inaccessible This typically leads to the only observable new effects being from φ, which in our setup is a weakly coupled sub-GeV state. We will introduce an explicit model that realizes our FOPT scenario
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