Radiatively generated fermion masses in SU(4)xSU(2)(L)xSU(2)(R)

We propose a model based on the gauge group SU(4) x SU(2)(L) x SU(2)(R) where the Dirac masses of all the known fermions are generated as one-loop radiative corrections. We are able to generate realistic quark and lepton masses and mixings without a large hierarchy of Yukawa couplings or extra symmetries. The neutrino masses, which are seesaw suppressed, lie in the mass range favored to solve the solar neutrino problem. The importance of threshold corrections to tree-level mass relations in certain nonsupersymmetric GUT's is demonstrated.