The Strong Isospin-Breaking Correction for the Gluonic Penguin   Contribution to epsilon'/epsilon at Next-to-Leading Order in the Chiral   Expansion
  The strong isospin-breaking correction, Omega_{st}, which appears in estimates of the Standard Model value for the direct CP-violating ratio epsilon'/epsilon, 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 1-loop and strong LEC contributions, are required for a complete determination at this order, are estimated using two different models. It is found that, to NLO, Omega_{st}=0.08 +/- 0.05, significantly reduced from the ``standard'' value, 0.25 +/- 0.08, employed in recent analyses. The potentially significant numerical impact of this decrease on Standard Model predictions for epsilon'/epsilon, associated with the decreased cancellation between gluonic penguin and electroweak penguin contributions, is also discussed. 
C. E. Wolfe (1), K. Maltman (2) ((1) Nuclear Theory Center, Indiana   Univ., Bloomington, USA, (2) Dept. of Math and Stats, ...