Application of chiral perturbation theory to K

Chiral perturbation theory is applied to the decay K2. It is shown that, to quadratic order in meson masses, the amplitude for K2 can be written in terms of the unphysical amplitudes K and K0, where 0 is the vacuum. One may then hope to calculate these two simpler amplitudes with lattice Monte Carlo techniques, and thereby gain understanding of the I=1/2 rule in K decay. The reason for the presence of the K0 amplitude is explained: it serves to cancel off unwanted renormalization contributions to K. We make a rough test of the practicability of these ideas in Monte Carlo studies. We also describe a method for evaluating meson decay constants which does not require a determination of the quark masses.