Towards a dynamical determination of parameters in the Minimal Supersymmetric Standard Model

In the Minimal Supersymmetric Standard Model (MSSM), the scale M_{SUSY} of soft supersymmetry breaking is usually {\em assumed} to be of the order of the electroweak scale. We reconsider here the possibility of treating M_{SUSY} as a dynamical variable. Its expectation value should be determined by minimizing the vacuum energy, after including MSSM quantum corrections. We point out the crucial role of the cosmological term for a dynamical generation of the desired hierarchies m_Z, M_{SUSY} << M_P. Inspired by four-dimensional superstring models, we also consider the Yukawa couplings as dynamical variables. We find that the top Yukawa coupling is attracted close to its effective infrared fixed point, corresponding to a top-quark mass in the experimentally allowed range. As an illustrative example, we present the results of explicit calculations for a special case of the MSSM.