MODELS OF FERMION MASS MATRICES BASED ON A FLAVOR-DEPENDENT AND GENERATION-DEPENDENT U(1) GAUGE-SYMMETRY

We study models of fermion mass matrices based on a flavor- and genera tion-dependent string-motivated U(1)(A) gauge symmetry and report two new classes of solutions to the requisite consistency conditions. In p articular, we explore the idea that the fundamental reason underlying the striking feature m(b), m(tau) much less than m(t) is that all of t he elements of the down-quark and charged lepton effective Yukawa matr ices actually arise from higher-dimension operators, suppressed by inv erse powers of the Planck mass. We construct an explicit model embodyi ng this idea, in which only the jk = 33 element of the Q = 2/3 effecti ve Yukawa matrix Y-jk(u) arises from dimension-4 operators.