Résumé
Nucl.Phys. B518 (1998) 3-36 We present, in the context of the Minimal Supersymmetric Standard Model, a detailed one-loop analytic study of the minimization conditions of the effective potential in the Higgs sector. Special emphasis is put on the role played by$Str M^4$in the determination of the electroweak symmetry breaking conditions, where first and second order derivatives of the effective potential are systematically taken into account. Novel, necessary (and sufficient in the Higgs sector) model-independent constraints, are thus obtained analytically, leading to new theoretical lower and upper bounds on$\tan \beta$ . Although fully model-independent, these bounds are found to be much more restrictive than the existing model-dependent ones! A first illustration is given in the context of a SUGRA-GUT motivated scenario.