LARGE-NC HIGHER-ORDER WEAK CHIRAL LAGRANGIANS COUPLED TO EXTERNAL ELECTROMAGNETIC-FIELDS - APPLICATIONS TO RADIATIVE KAON DECAYS

Using factorization and bosonization of quark currents derived from the anomalous Wess-Zumino-Witten terms and from the electroweak perturbations to a QCD-motivated model for nonanomalous p4 chiral Lagrangians, we obtain leading 1Nc fourth-order S=1 weak chiral Lagrangians coupled to external electromagnetic fields, valid to the zeroth order of gluonic corrections. Applications to radiative K decays, e.g., K*l+l-, K, K, and Kl, are studied. The twofold ambiguity for the predictions of Kl+l- is suggestively resolved. The branching ratio of K±± is predicted to be 5.1 × 10-7, while the current upper bound based on a pion phase-space spectrum is 10-6. The direct K±±0 decays offer an excellent test on both anomalous and nonanomalous weak chiral Lagrangians; the agreement between theory and experiment is marvelous. The branching ratio of the interference between innerbremsstrahlung and direct-emission amplitudes in the process KLe is found to be of order 10-5. © 1990 The American Physical Society.