Effects of Superheavy Quarks and Leptons in Low-Energy Weak Processes KL-> Formula, K+-> + Formula and K0 Formula

We investigate potentially important effects due to the existence of superheavy quarks and leptons of the sequential type in higher·order weak processes at low energies. The second-order LlS * 0 neutral-current processes Kl. ~ I'ii, K~ 1[+ vi) and KL-Ks mass difference are analysed allowing for fermions of masses comparable to or larger than the weak-boson mass in the Kobayashi-Maskawa scheme and in the general sequential scheme with an arbitrary number of generations. Possible connection between heavy·quark masses and light-heavy quark mixing are also examined. The requirement that the rare decay processes such as KL ~ l1ii and K+ ~ 1[+ vi) be absent up to order aGF yields a rather stringent bound on the magnitude of light-heavy Quark mixing: Such mixing has to be less than mW/mQuack times a factor much smaller than unity.