Long vs. short distance dispersive two-photon K_L \to \mu^+ \mu^- amplitude

Abstract

We report on the calculation of the two-loop electroweak, two-photon mediated short-distance dispersive K_L \to \mu^+\mu^- decay amplitude. QCD corrections change the sign of this contribution and reduce it by an order of magnitude. The resulting amplitude enables us to provide a constraint on the otherwise uncertain long-distance dispersive amplitude.

Comments: 5 pages, 2 figures, presented by K.K. on the conference "Nuclear and Particle Physics with CEBAF", Dubrovnik, Croatia, Nov 3-10, 1998