Four-generation low energy supersymmetry with a light top quark

A supersymmetric model with four generations is proposed, in which the top quark is approximately degenerate in mass with the W^{\pm} gauge boson, m_t\simeq m_W, leading to values of R_b in better agreement with the present experimental data than in the Standard Model. The model shares many of the good features of the minimal supersymmetric extension of the Standard Model (MSSM), such as the unification of gauge and Yukawa couplings at a common high-energy scale. The model differs from the MSSM by re-interpreting the Tevatron ``top-quark'' events as the production of the fourth generation quark t\pri, which decays dominantly to bW^+. The top quark decays primarily into supersymmetric particles, t\rta\widetilde t\widetilde\chi^0_1, with \widetilde t\rta c\widetilde\chi^0_1, thereby evading previous searches. Light supersymmetric particles are predicted to lie in the mass range between 25 and 70 GeV, which together with the fourth generation leptons provide a rich spectrum of new physics which can be probed at LEP-2 and the Tevatron.