The strong isospin-breaking correction for the gluonic penguin contribution to epsilon '/epsilon at next-to-leading order in the chiral expansion - art. no. 014008

The strong isospin-breaking correction Omega (st), which appears in estimat es of the standard model value for the direct CP-violating ratio epsilon'/e psilon, is evaluated to next-to-leading order (NLO) in the chiral expansion using chiral perturbation theory. The relevant linear combinations of the unknown NLO CP-odd weak low-energy constants (LEC's) which, in combination with one-leap and strong LEC contributions, are required for a complete det ermination at this order, are estimated using two different models. It is f ound that, to NLO, Omega (st)=0.08 +/- 0.05, significantly reduced from the "standard" value, 0.25+/-0.08, employed in recent analyses. The potentiall y significant numerical impact of this decrease on standard model predictio ns for epsilon'/epsilon, associated with the decreased cancellation between gluonic penguin and electroweak penguin contributions, is also discussed.