$K\to\pi\pi$ Decays in SU(2) Chiral Perturbation Theory

Abstract

We study the decays $K\to\pi\pi$ in one-loop two-flavour Chiral Perturbation Theory. We provide arguments why the calculation of the coefficient of the pionic chiral logarithm $\logm = M^2\log M^2$ is unique and then perform the calculation. As a check we perform the reduction of the known three-flavour result. The underlying arguments are expected to be valid for heavier particles and other processes as well.