Ksub(L) -> μ+μ-, top mass and bottom lifetime

We study a class of diagrams, that has previously overlooked, contributing to the (dispersive) electromagnetic part of the Ksub(L) -> μ+μ- amplitude. The strength of this extra contribution can be estimated in different models and could be measured in related processes. By combining these results with those coming from the K0-anti K0 transition (evaluated in the Kobayashi-Maskawa scheme) we obtain rather strong constraints on the t quark mass and the B meson lifetime. The recently measured value for the B meson lifetime is difficult to accommodate unless the t quark is very heavy; msub(t) > 100 GeV could be natural values according to the analysis. (orig.)