2-LOOP LARGE-M(T) ELECTROWEAK CORRECTIONS TO K-]PI-NU(NU)OVER-BAR FORAN ARBITRARY HIGGS-BOSON MASS

We consider for the first time the leading, large top quark mass corre ctions, arising at higher order in electroweak interactions, to the ra re decays K-->pi nu<(nu)over bar> and the related modes B-->X-s nu<(nu )over bar> and B-->l(+)l(-). Higher order effects of similar type have previously been calculated in the large-m(t) limit for key observable s of precision electroweak physics at Z factories. Here we obtain the corresponding corrections of order O(G(F)(2)m(t)(4)) at the amplitude level for short-distance dominated rare meson decays. This allows us t o quantify the importance of higher order electroweak effects for thes e processes, which can be reliably computed and have very small uncert ainties from strong interactions. Simultaneously it becomes possible t o remove, to some extent, ambiguities in the definition of electroweak parameters describing the strength of flavor-changing neutral current interactions. The corrections we discuss are at the level of a few pe rcent. [S0556-2821(98)02001-3].