Including electromagnetism in K->pipi decay calculations
Because of the small size of the ratio $A_2/A_0$ of the $I=2$ to $I=0$ $K\to\pi\pi$ 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 $\varepsilon'/\varepsilon$ 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 $K\to\pi\pi$ decay amplitudes using lattice QCD.
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Weak Decays and Matrix Elements