# Direct CP violation in $D^+ \to K^0(\bar K^0) \pi^+$ decays as a probe for new physics

## TL;DR

This paper investigates direct CP violation in charged D meson decays, showing that standard model predictions are negligible, but certain new physics models can produce significantly larger CP asymmetries, making these decays promising probes for new physics.

## Contribution

The study calculates CP asymmetries in D+ decays within the standard model and explores enhancements possible in two Higgs doublet and left-right symmetric models, highlighting their potential to reveal new physics.

## Key findings

- Standard model predicts CP asymmetry of order 10^{-11}
- Two Higgs doublet model can enhance asymmetry by 6-7 orders of magnitude
- Left-right symmetric models can produce asymmetries around 10^{-3}

## Abstract

In this paper we investigate CP violation in charged decays of $D$ meson. Particularly, we study the direct CP asymmetry of the Cabibbo favored non-leptonic $D^+ \rightarrow \bar K^0 \pi^+$ and the doubly Cabibbo-suppressed decay mode $D^+ \rightarrow K^0 \pi^+$ within standard model, two Higgs doublet model with generic Yukawa structure and left right symmetric models. In the standard model, we first derive the contributions from box and di-penguin diagrams contributing to their amplitudes which are relevant to the generation of the weak phases essential for non-vanishing direct CP violation. Then, we show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-11}$ in both decay modes. Regarding the two Higgs doublet model with generic Yukawa structure and after taking into account all constraints on the parameter space of the model, we show that the enhanced direct CP asymmetries can be 6 and 7 orders of magnitudes larger than the standard model prediction for $D^+ \rightarrow \bar K^0 \pi^+$ and $D^+ \rightarrow K^0 \pi^+$ respectively. Finally, within left right symmetric models, we find that sizable direct CP asymmetry of ${\mathcal O } (10^{-3})$ can be obtained for the decay mode $D^+ \rightarrow \bar K^0 \pi^+$ after respecting all relevant constraints.