The self-penguin contribution to K->2 pi

We consider the contribution to K --> 2 pi decays from the non-diagonal s --> d quark transition amplitude. First, we calculate the most important part of the s --> d transition, the so-called self-penguin amplitude similar to G(F) alpha(s), including the heavy top-quark case. Second, we calculate the matrix element of the s --> d transition for the physical K --> 2 pi process. This part of the analysis is performed within the Chiral Quark Model where quarks are coupled to the pseudoscalar mesons. The CP-conserving self-penguin contribution to K --> 2 pi is found to be negligible. The obtained contribution to epsilon'/epsilon is sensitive to the values of the quark condensate [(q)over bar>q] and the constituent quark mass M. For reasonable values of these quantities we find that the self-penguin contribution to epsilon'/epsilon is 10-15% of the gluonic penguin contribution and has the same sign. Given the large cancellation between gluonic and electroweak penguin contributions, this means that our contribution is of the same order of magnitude as epsilon'/epsilon itself.