Quark and lepton masses from renormalization-group fixed points

The renormalization-group equations describing the evolution of fermion-Higgs-boson Yukawa coupling constants down from MX in a grand unified theory possess fixed points which may lead to universal predictions for fermion masses independent of symmetry considerations at MX. Our analysis predicts {≈} 240 GeV for the fixed-pint t-quark mass. Alternatively, a sufficiently heavy fourth SU(5) generation cannot be ruled out by existing bounds on the number of fermion generations, nf, and we find fixed-point mass predictions of mT≈219 GeV, mB≈215 GeV, and mE≈60 GeV.