  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.

High Energy Physics - Phenomenology;High Energy Physics - Experiment