Additional Isospin-Breaking Effects in \epsilon^\prime/\epsilon

Abstract

In the analysis of \epsilon^\prime/\epsilon it has been traditional to consider the isospin-breaking effects arising from electroweak-penguin contributions and from \pi^0-\eta and \pi^0-\eta^\prime mixing, yet additional isospin-violating effects exist. In particular, we study the isospin violation which arises from the u-d quark mass difference in the hadronization of the gluonic penguin operator, engendering contributions of an effective \Delta I=3/2 character. 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 \epsilon^\prime/\epsilon by a factor of two.

Comments: 11 pages, LaTeX; notational errors rectified, refs. added, footnote corrected