Additional Isospin-Breaking Effects in epsilon'/epsilon

Abstract

Isospin-breaking effects, in particular those associated with electroweak-penguin contributions and pi0-eta,eta' mixing, have long been known to affect the Standard Model prediction of Re(epsilon'/epsilon) in a significant manner. We have found an heretofore unconsidered isospin-violating effect of importance; namely, the u-d quark mass difference can spawn |Delta I|=3/2 components in the matrix elements of the gluonic penguin operators. Using chiral perturbation theory and the factorization approximation for the hadronic matrix elements, we find within a specific model for the low-energy constants that we can readily accommodate an increase in Re(epsilon'/epsilon) by a factor of two.