The conventional left-right gauge model based on the group SU(3)×SU(2${)}_{\mathrm{L}}$×SU(2${)}_{\mathrm{R}}$×U(1) is extended to include singlet quarks and leptons but the usual Higgs-boson doublet-doublet is replaced by two doublet-singlets and two singlet-doublets. As a result, realistic radiative masses for light quarks and leptons can be obtained. Neutrino masses are further suppressed by the seesaw mechanism. There is no need for any assumed discrete symmetry.

• Received 24 February 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.1042