Radiative three-body D-meson decays in and beyond the standard model

We study radiative charm decays D -> P1P2 gamma, P1,2=pi ,K in QCD factorization at leading order and within heavy hadron chiral perturbation theory. Branching ratios including resonance contributions are around similar to 10-3 for the Cabibbo-favored modes into K pi gamma and similar to 10-5 for the singly Cabibbo-suppressed modes into pi+pi-gamma ,K+K-gamma, and thus in reach of the flavor factories BES III and Belle II. Dalitz plots and forward-backward asymmetries reveal significant differences between the two QCD frameworks; such observables are therefore ideally suited for a data-driven identification of relevant decay mechanisms in the standard-model dominated D -> K pi gamma decays. This increases the potential to probe new physics with the D -> pi+pi-gamma and D -> K+K-gamma decays, which are sensitive to enhanced dipole operators. CP asymmetries are useful to test the SM and look for new physics in neutral |Delta C|=1 transitions. Cuts in the Dalitz plot enhance the sensitivity to new physics due to the presence of both s- and t, u-channel intermediate resonances.

Automated summary

The study investigates radiative charm decays in QCD factorization and heavy hadron chiral perturbation theory, revealing differences in branching ratios and observables between the two frameworks. These differences can help in identifying relevant decay mechanisms and probing new physics in standard-model dominated decays, potentially with enhanced sensitivity to new physics through specific cuts in the Dalitz plot.