A consistent picture for large penguins in D → π ⁺π ^-, K ⁺K ^-

A long-standing puzzle in charm physics is the large difference between the D ⁰→ K ⁺K ^- and D ⁰→ π ⁺π ^- decay rates. Recently, the LHCb and CDF collaborations reported a surprisingly large difference between the direct CP asymmetries, ΔACP, in these two modes. We show that the two puzzles are naturally related in the Standard Model via s- and d-quark "penguin contractions". Their sum gives rise to ΔACP, while their difference contributes to the two branching ratios with opposite sign. Assuming nominal SU(3) breaking, we perform a U-spin based fit to the D ⁰ → K ⁺π ^-; π ⁺K ^- ; π ⁺π ^- ;K ⁺K ^- decay rates, which yields large penguin contractions that naturally explain ΔACP. Expectations for the individual CP asymmetries are also discussed.