Rare kaon decays revisited

Abstract

We present an updated discussion of K→πl̄l decays in a combined framework of chiral perturbation theory and large-Nc QCD, which assumes the dominance of a minimal narrow resonance structure in the invariant mass dependence of the l̄l pair. The proposed picture reproduces very well, both the experimental K+→π+e+e− decay rate and the invariant e+e− mass spectrum. The predicted Br(KS→π0e+e−) is, within errors, consistent with the recently reported result from the NA48 Collaboration. Predictions for the K→πμ+μ− modes are also obtained. We find that the resulting interference between the direct and indirect CP-violation amplitudes in KL→π0e+e− is constructive.