UNIFIED THEORIES WITH U(2) FLAVOR SYMMETRY

A general operator expansion is presented for quark and lepton mass ma trices in unified theories based on a U(2) flavor symmetry, with break ing parameter of order V-cb approximate to m(s)/m(b) approximate to ro ot m(c)/m(t). While solving the supersymmetric flavor-changing problem , a general form for the Yukawa couplings follows, leading to nine rel ations among the fermion masses and mixings, five of which are precise . The combination of grand unified and U(2) symmetries provides a symm etry understanding for the anomalously small values of m(u)/m(c) and m (c)/m(t). A fit to the fermion mass data leads to a prediction for the angles of the CKM unitarity triangle, which will allow a significant test of these unified U(2) theories. A particular SO(10) model provide s a simple realization of the general operator expansion. The lighter generation masses and the non-trivial structure of the CKM matrix are generated from the exchange of a single U(2) doublet of heavy vector g enerations. This model suggests that CP is spontaneously broken at the unification scale-in which case there is a further reduction in the n umber of free parameters. (C) 1997 Elsevier Science B.V.