Long distance contribution to K+->pi(+)nu(nu)over-bar at O(p(4)) in ChPT

We calculate the long distance contributions to K+ --> pi(+) nu(nu)over-bar within the framework of chiral perturbation theory (ChPT). We derive a gen eral form of the weak Lagrangian of O(p(4)) in the chiral expansion from th e factorization model. We estimate the decay branching ratio of K+ --> pi() nu(nu)over-bar at the level of O(p(4)) for both tree and complete one-loo p contributions, and compare our results with those in the literature.