Isospin-violating contributions to ∈′/∈

The known isospin-breaking contributions to the K → ππ amplitudes are reanalyzed, taking into account our current understanding of the quark masses and the relevant non-perturbative inputs. We present a complete numerical reappraisal of the direct CP-violating ratio ∈′/∈, where these corrections play a quite significant role. We obtain the Standard Model prediction Re (∈′/∈) = (14 ± 5) · 10−4, which is in very good agreement with the measured ratio. The uncertainty, which has been estimated conservatively, is dominated by our current ignorance about 1/NC-suppressed contributions to some relevant chiral-perturbation-theory low-energy constants.