Phenomenological and cosmological aspects of the breaking of the electroweak and global symmetries in the MSSM and the NMSSM

The predictions of the MSSM are discussed in the light of recent LEP and SL D precision data. The full supersymmetric one-loop corrections to the effec tive weak mixing angle are considered. Potentially dangerous, large logarit hmic sparticle corrections are cancelled. The relative difference factor De lta k between the mixing angle defined as a ratio of couplings and the expe rimentally obtained angle is discussed and it is found that Delta k is domi nated by the oblique corrections, while the non-oblique overall supersymmet ric EW and SQCD corrections are negligible. We also reconsider the next to minimal supersymmetric standard model (NMSSM) as a natural solution to the mu problem and show that both the stability and the cosmological domain wal l problems are eliminated if we impose a discrete Z(2) R-symmetry on the no n-renormalizable operators of the theory.