Phenomenology of supersymmetric models with a singlet

The supersymmetric extension of the standard model with an additional gauge singlet is analysed in detail in the light of the recent experimental bounds on supersymmetric particles. The useful part of the parameter space and the particle spectrum are displayed. We find that once the recent bounds on the chargino mass are imposed, all other new particles practically satisfy the present experimental limits. Special attention is given to particles to be searched for in the future experiments. The singlet fields tend to decouple and give rise to an effective MSSM, enlarging the validity of many phenomenological analyses based in the minimal field content. However, in some ranges of the parameters the singlino is the lightest neutralino, which modifies the signature for susy particles. Simple analytical approximations are developed that qualitatively explain the numerical results.