OFF-SHELL S-]D TRANSITIONS IN K-DECAYS

In an attempt to go beyond the free quark mass-shell, we reveal new contributions to K-meson decays. We account for them by using an effective low-energy QCD, advocated by many authors, where the quarks are coupled to the pseudoscalar mesons pi, K, eta. These couplings are due to their Goldstone character, and reflect chiral-symmetry breaking. Within this scheme we find explicitly that, for the decays K --> pipi and K --> gammagamma, the physical effects of operators involving (igamma.D - m(q)) are not zero, contrary to current statements. To be more specific, one obtains a zero effect only in the limit when the quark-meson interactions are switched off, that is for f(pi) --> infinity. Numerically, we find weak impact on the CP-conserving K --> pipi amplitude, while the impact on K --> gammagamma is substantial in the CP-violating case.