4-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-+/- gauge bo son, m(t) similar or equal to m(W), leading to values of R(b) in bette r agreement with the present experimental data than in the Standard Mo del. The model shares many of the good features of the minimal supersy mmetric extension of the Standard Model (MSSM), such as the unificatio n of gauge and Yukawa couplings at a common high energy scale. The mod el differs from the MSSM by re-interpreting the Tevatron ''top-quark'' events as the production of the fourth generation quark t', which dec ays dominantly to bW(+). The top quark decays primarily into supersymm etric particles, t --> (t) over tilde<(chi)over tilde (0)(1)>, with (t ) over tilde --> <c(chi)over tilde (0)(1)>, thereby evading previous s earches. Light supersymmetric particles are predicted to lie in the ma ss range between 25 and 70 GeV, which together with the fourth generat ion leptons provide a rich spectrum of new physics which can be probed at LEP-2 and the Tevatron.