Comments on long distance contribution to K+ → π+νν

We study the long distance contribution to K+ → π+νν by using chiral perturbation theory. We find that the tree level O(P2) contribution vanishes identically without assuming the large Nc limit. The leading contribution arises from the one-loop amplitude, which is O(P4) in the chiral power counting. The branching ratio of the long distance contribution is found to be of order 10−7 smaller compared with that of short distance one and hence is completely negligible.