The Mssm with Large Tan Β beyond the Decoupling Limit *

The Minimal Supersymmetric Standard Model (MSSM) contains two Higgs doublets Hu and Hd coupling to upand down-type quark fields, respectively. The neutral components of these Higgs doublets acquire vacuum expectation values (vevs) vu and vd with the sum v 2 u+v 2 d being fixed to v ≈ (174 GeV) and the ratio tan β ≡ vu/vd remaining as a free parameter. Large values of tanβ (∼ 50) are theoretically motivated by bottom-top Yukawa unification, which occurs in SO(10) GUT models with minimal Yukawa sector, and phenomenologically preferred by the anomalous magnetic moment of the muon [1]. Since a large value of tanβ corresponds to vd ≪ vu, it leads to enhanced corrections in amplitudes where the treelevel contribution is suppressed by the small vev vd but the loop-correction involves vu instead. In such cases the ratio of one-loop to tree-level contribution receives an enhancement-factor tan β which may lift the loopsuppression rendering the ratio of order O(1). In order not to spoil the perturbative expansion a special treatment is required for these tanβ-enhanced corrections to resum them to all orders. There are two possible ways to deal with them. The first is to