Low-energy limits of theories with two supersymmetries

Given its non-renormalization properties, low-energy supersymmetry provides an attractive framework for extending the standard model and for resolving the hierarchy problem. Models with softly broken $N=1\mathrm{}$ supersymmetry have been extensively studied and are phenomenologically successful. However, it could be that an extended $N=2\mathrm{}$ supersymmetry survives to low energies, as suggested by various constructions. We examine the phenomenological viability and implications of such a scenario. We show that consistent chiral fermion mass generation emerges in $N=2\mathrm{}$ theories, which are vectorial, as a result of supersymmetry breaking at low energies. A rich mirror quark and lepton spectrum near the weak scale with model-dependent decay modes is predicted. A $Z_2$ mirror parity is shown to play an important role in determining the phenomenology of the models. It leads, if conserved, to a new stable particle, the LMP. Consistency of the $N=2\mathrm{}$ framework and its unique spectrum with electroweak precision data is considered, and the discovery potential in the next generation of hadron collider experiments is stressed. Mirror quark pair production provides the most promising discovery channel. Higgs boson searches are also discussed and it is shown that there is no upper bound on the prediction for the Higgs boson mass in the framework of low-energy supersymmetry breaking, in general, and in the $N=2\mathrm{}$ framework, in particular. Possible $N=2\mathrm{}$ realizations of flavor symmetries and of neutrino masses are also discussed.