Shedding Light on CP Violation in the Charm System via D → V γ Decays

Recent evidence for direct CP violation in nonleptonic charm decays cannot be easily accommodated within the standard model. On the other hand, it fits well in new physics models generating CP violating Delta C = 1 chromomagnetic dipole operators. We show that in these frameworks sizable direct CP asymmetries in radiative D -> P+ P- gamma decays (P = pi, K), with M (PP) close to the rho or the phi peak, can be expected. Enhanced matrix elements of the electromagnetic dipole operators can partly compensate the long distance dominance in these decays, leading to CP asymmetries of the order of several percent. If observed at this level, these would provide a clean signal of physics beyond the standard model and of new dynamics associated with dipole operators. We briefly comment on related CP violating observables accessible via time dependent D((D) over bar) -> P+ P- gamma studies and angular decay product distributions in rare semileptonic D decays.