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

TL;DR

This paper discusses the importance of including electromagnetic effects in lattice QCD calculations of K to pi pi decay amplitudes to improve the accuracy of theoretical predictions related to the Delta I=1/2 rule.

Contribution

It presents initial steps toward incorporating electromagnetism into lattice QCD calculations of K to pi pi decays, addressing a significant source of correction.

Findings

Electromagnetic effects on A_2 may be 20 times larger than naive estimates.

Including electromagnetism is necessary for 10% accuracy in future calculations.

First steps toward lattice QCD inclusion of electromagnetism in decay amplitudes.

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.