$b \to s\gamma$, electron EDM and electroweak baryogenesis: a study in general 2HDM

Abstract

We study inclusive $b \to s\gamma$ decay in the context of electron EDM and baryogenesis. The general 2HDM (i.e. without $Z_2$) that possesses an extra set of Yukawa matrices can drive electroweak baryogensis via $\lambda_t {\rm Im}\rho_{tt}$, where $\rho_{tt}$ is the extra diagonal top Yukawa coupling, with the $e$EDM constraint evaded by an exquisite flavor cancellation mechanism. We touch upon the current status of direct search for exotic $H$, $A$ and $H^+$ scalars at the LHC, while for the plethora of flavor observables in $g$2HDM, we focus on $b\to s\gamma$, pointing out $chiral$ enhancement of a $\rho_{tt}\rho_{bb}$ effect in $g$2HDM, which can bring in a CPV phase. We first explore the inclusive ${\cal B}(b \to s\gamma)$ rate, then showcase the progress that Belle II can make in the future, illustrating a potential 3$\sigma$ effect for the inclusive $B^+ \to X_s^+\gamma$ vs $B^0 \to X_s^0\gamma$ CPV rate difference, $\Delta A_{\rm CP}$. Especially if $e$EDM emerges swiftly, perhaps one should pursue further upgrade beyond Belle II.