Including electromagnetism in $K\to\pi\pi$ decay calculations

Abstract

Because of the small size of the ratio A_2/A_0 of the I=2 to I=0 K -> pipi decay amplitudes (the Delta I=1/2 rule) the effects of electromagnetism on A_2 may be a factor of 20 larger than given by a naive O(alpha) estimate. Thus, if future calculations of A_2 and epsilon'/epsilon are to achieve 10% accuracy, these effects need to be included. Here we present the first steps toward including electromagnetism in a calculation of the standard model K -> pipi decay amplitudes using lattice QCD.