Long-distance contribution to the muon-polarization asymmetry in K+→π+μ+μ- -: art. no. 076001

We reexamine the calculation of the long-distance contribution to the muon-polarization asymmetry Delta(LR), which arises, in K+-->pi(+)mu(+)mu(-), from the two-photon intermediate state. The parity-violating amplitude of this process, induced by the local anomalous K(+)pi(-)gamma(*)gamma(*) transition, is analyzed; unfortunately, one cannot expect to predict its contribution to the asymmetry by using chiral perturbation theory alone. Here we evaluate this amplitude and its contribution to Delta(LR) by employing a phenomenological model called the FMV model (factorization model with vector couplings), in which the use of the vector and axial-vector resonance exchange is important to soften the ultraviolet behavior of the transition. We find that the long-distance contribution is of the same order of magnitude as the standard model short-distance contribution.