Short- and long-distance contributions to the rare decay KL → μ+μ−

Abstract

The interplay between short- and long-distance contributions to the K L → μ + μ − decay amplitude is analyzed. The long-distance piece is estimated using chiral perturbation theory techniques and large- N c considerations, leading to a consistent description of the π 0 → e + e −, η → μ + μ −, and K L → μ + μ − branching ratios [1].