Virtual photon correction to the K+→π+π0π0 decay

We consider electromagnetic corrections to the nonleptonic kaon decay, K+→π+π0π0, due to explicit virtual photons only. The decay amplitude is calculated at a one-loop level in the framework of chiral perturbation theory. The interest in this process is twofold: It is actually measured by the NA48 Collaboration from one side, and, the value of the amplitude at the ππ threshold gives access to ππ scattering lengths from the other side. We found that the present correction is about 5 to 6% the value of the Born amplitude squared. Combined with another paper published recently, this fixes the size of the isospin breaking correction to the amplitude squared to 7% its one-loop level value in the absence of isospin breaking and at the center of the Dalitz plot