IMPACT OF A LARGE FB ON RARE KAON DECAYS

We examine the effects of a large B-meson decay constant f(B) which has been obtained by recent lattice QCD calculations on rare K decays. We find that the short-distance contributions to the branching ratios of CP conserving decays such as K(L) --> mu-mu-BAR and K+ --> pi+-nu-nu-BAR much smaller than previously expected and estimated to be in the tighter ranges of (0.2-1.5)X 10(-9) and (0.4 - 1.6) X 10(-10), respectively, whereas that of CP violating ones K(L) --> pi-0e+e- and K(L) --> pi-0-nu-nu-BAR are enhanced with f(B) = 250 +/- 50 MeV, m(c) = 1.2-1.8 GeV and m(t) = 90-200 GeV.