CP violation in $D^0 \to K^+ \pi^- $

TL;DR

This paper analyzes the direct CP asymmetry in the decay $D^0 o K^+ \pi^-$ within the Standard Model and a two Higgs doublet model, finding the latter can produce significantly larger asymmetries.

Contribution

It provides a detailed calculation of CP asymmetry contributions in both the Standard Model and a two Higgs doublet model with generic Yukawa couplings, highlighting potential new physics effects.

Findings

Standard Model predicts CP asymmetry of order 10^{-9}.

Two Higgs doublet model can enhance CP asymmetry to order 10^{-3}.

Charged Higgs couplings significantly increase CP violation potential.

Abstract

In this paper we study the direct CP asymmetry of the doubly Cabibbo-suppressed decay mode $D^0 \to K^+ \pi^- $ within standard model and two Higgs doublet model with generic Yukawa structure. In the standard model we derive the corrections to the tree level amplitude, generated from the box and di-penguin diagrams, required for generating the weak CP violating phases. We show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-9}$. Regarding the two Higgs doublet model with generic Yukawa structure we derive the Wilson coefficients relevant to $D^0 \to K^+ \pi^- $. After taking into account all constraints on the parameter space of the model we show that charged Higgs couplings to quarks can lead to a direct CP asymmetry of order $10^{-3}$ which is $6$ orders of magnitude larger than the standard model prediction.