# Repercussions of flavour symmetry breaking on CP violation in D-meson decays

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## Abstract

We investigate to what extent the recently measured value for a non-vanishing direct CP asymmetry in *D* ^{0} → *K* ^{+} *K* ^{−} and D^{0} → *π* ^{+} *π* ^{−} decays can be accommodated in the Standard Model (SM) or extensions with a constrained flavour sector, for instance from a sequential 4^{th} generation of quarks (4 G). From the comparison with *D* ^{0} → *K* ^{−} *π* ^{+} branching ratios, we establish large U-spin symmetry (*d* ↔ *s*) breaking effects with large strong phases between different interfering amplitudes. On the basis of conservative estimates on amplitude ratios — which are supported by an analysis of the breaking of a *c* ↔ *u* symmetry in non-leptonic B^{0} decays — we find that, in the SM, direct CP asymmetries in the *π* ^{+} *π* ^{−} or *K* ^{+} *K* ^{−} modes (or in their difference) of the order of several per mille are still plausible. Due to the constraints on the new CP phases in the 4 G model, only moderate effects compared to the SM estimates are possible. We suggest CP studies at LHCb as well as at (Super)B-factories of several distinctive modes, such as *D* + → \( \overline K \) ^{(∗)0} *π* ^{+}, *ϕπ* ^{+} and *D* _{ s } → *K* ^{(∗)0} *π* ^{+}, *ϕπ* ^{+}(*K* ^{+}) etc., which should shed more light on the short- and long-distance issues underlying CP violation in non-leptonic D-meson decays.

## Keywords

Rare Decays CP violation Standard Model Beyond Standard Model## References

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