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Direct CP violation in the hadronic charm decays provides a good testingground for the Kobayashi-Maskawa mechanism in the Standard Model. Anysignificant deviations from the expectation would be indirect evidence ofphysics beyond the Standard Model. In view of improved measurements from LHCband BESIII experiments, we re-analyze the Cabibbo-favored $D \to P\!P$ and$V\!P$ decays in the topological diagram approach. By assuming certainSU(3)-breaking effects in the tree-type amplitudes, we make predictions forboth branching fractions and CP asymmetries of the singly Cabibbo-suppresseddecay modes. While the color-allowed and -suppressed amplitudes are preferredto scale by the factor dictated by factorization in the $P\!P$ modes, no suchscaling is required in the $V\!P$ modes. The $W$-exchange amplitudes are foundto change by 10\% to 50\% and depend on whether $d\overline{d}$ or$s\overline{s}$ pair directly emerges from $W$-exchange. The predictions ofbranching fractions are generally improved after these SU(3) symmetry breakingeffects are taken into account. We show in detail how the tree-type,QCD-penguin, and weak penguin-annihilation diagrams contribute and modify CPasymmetry predictions. Future measurements of sufficiently many direct CPasymmetries will be very useful in removing a discrete ambiguity in the strongphases as well as discriminating among different theory approaches. Inparticular, we predict $a_{CP}(K^+K^-)-a_{CP}(\pi^+\pi^-) = (-1.14 \pm 0.26)\times 10^{-3}$ or $(-1.25 \pm 0.25) \times 10^{-3}$, consistent with thelatest data, and $a_{CP}(K^+K^{*-})-a_{CP}(\pi^+\rho^-) = (-1.52 \pm 0.43)\times 10^{-3}$, an attractive and measurable observable in the near future.Moreover, we observe that such CP asymmetry differences are dominated bylong-distance penguin-exchange through final-state rescattering.

Revisiting CP violation in $D\to P\!P$ and $V\!P$ decays