Optimal charge and color breaking conditions in the MSSM

In the MSSM, we make a careful tree-level study of charge and color breaking conditions in the plane (H-2, (u) over tilde (L), (u) over tilde (R)), focusing on the top quark scalar case. A simple and fast procedure to compute the VEVs of the dangerous vacuum is presented and used to derive a model-independent optimal CCB bound on At. This bound takes into account all possible deviations of the CCB vacuum from the D-flat directions. For large tan beta, it provides a CCB maximal mixing for the stop scalar fields (t) over tilde (1), (t) over tilde (2), which automatically rules out the Higgs maximal mixing \A(t)\ = root 6m((t) over tilde). As a result, strong limits on the stop mass spectrum and a reduction, in some cases substantial, of the one-loop upper bound on the CP-even lightest Higgs boson mass, m(h), are obtained. To incorporate one-loop leading corrections, this tree-level CCB condition should be evaluated at an appropriate renormalization scale which proves to be the SUSY scale. (C) 2001 Elsevier Science B.V. All rights reserved.