$\epsilon'_K/\epsilon_K$ and $K \to \pi \nu \bar\nu$ in a two-Higgs doublet model

TL;DR

This paper investigates how charged-Higgs contributions in a two-Higgs-doublet model can account for the observed Kaon direct CP violation and predict rare decay rates, offering testable predictions for upcoming experiments.

Contribution

It demonstrates that charged-Higgs effects can enhance Kaon CP violation and rare decay branching ratios within a two-Higgs-doublet model, consistent with existing constraints.

Findings

Kaon direct CP violation can reach ~8 x 10^{-4} from charged-Higgs effects.

Predicted branching ratios for rare decays are BR(K+→π+νν̄)~14 x 10^{-11} and BR(KL→π0νν̄)~3.6 x 10^{-11}.

Results are testable by NA62 and KOTO experiments.

Abstract

The Kaon direct CP violation $Re(\epsilon'_K/\epsilon_K)$ below the experimental data of a $2\sigma$ in the standard model, which is calculated using the RBC-UKQCD lattice and a large $N_c$ dual QCD, indicates the necessity of a new physics effect. In order to resolve the insufficient $Re(\epsilon'_K/\epsilon_K)$, we study the charged-Higgs contributions in a generic two-Higgs-doublet model. If we assume that the origin of the CP-violation phase is uniquely from the Kobayashi-Maskawa (KM) phase when the constraints from the $B$- and $K$-meson mixings, $B\to X_s \gamma$, and Kaon indirect CP violating parameter $\epsilon_K$ are simultaneously taken into account, it is found that the Kaon direct CP violation through the charged-Higgs effects can reach $Re(\epsilon'_K/\epsilon_K)_{H^\pm}\sim 8 \times 10^{-4}$. Moreover, with the constrained values of the parameters, the branching ratios of the rare $K\to \pi \nu \bar\nu$ decays can be $BR(K^+\to \pi^+ \nu \bar\nu)\sim 14 \times 10^{-11}$ and $BR(K_L\to \pi^0 \nu \bar\nu)\sim 3.6 \times 10^{-11}$, where the results can be tested through the NA62 experiment at CERN and the KOTO experiment at J-PARC, respectively.