V. Cirigliano, H. Gisbert, A. Pich, Antonio Rodriguez-Sánchez
Isospin-violating contributions to ε'/ε


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 ε'/ε, where these corrections play a quite significant role. We obtain the Standard Model prediction Re (ε'/ε) = (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/N_C-suppressed contributions to some relevant chiral-perturbation-theory low-energy constants.

LU TP 19-51