LEADING NONLOGARITHMIC CONTRIBUTION TO THE ELECTROPENGUIN DIAGRAM AND PHENOMENOLOGY OF KAON DECAYS

The leading non-logarithmic contribution which arises in the real part of the Wilson coefficient for the electropenguing operator is re-analized within the four-flavor effective Hamiltonian. The ratio Gamma(K+--->pi+ e+ e-)/Gamma(K+--->pi0 e+ nu_e), the K_L--->pi0 e+ e- decay rate and the Delta I=1/2 rule in the non-leptonic kaon decays are reconsidered by taking into account both the leading non-logarithmic contribution and the strong corrections in log(M_W/mu)^2 up to the next-to-leading order. Their dependence on the QCD parameters is studied and we argue that the inclusion of the strong corrections of order log(m_g/mu)^2 cannot be neglected.