Can the rho parameter allow for the existence of a nondegenerate fourth family?

Abstract

The question of mass splitting within a doublet of heavy fermions, in particular a fourth generation of quarks and leptons, is reexamined with emphasis on the contribution of possible heavy-fermion ``vector-meson'' bound states to the \ensuremath{\rho} parameter. The heavy-fermion bound states are formed by the exchange of the Higgs boson. We have found that, in the minimal model, the constraint on mass splitting which now also depends on the Higgs boson mass gives rise to some interesting phenomena, including the possibility of having a top-quark mass greater than 180 GeV.