New fermion mass textures from anomalous U(1) symmetries with baryon and lepton number conservation

In this paper we present solutions to the fermion mass hierarchy problem in the context of the minimal supersymmetric standard theory augmented by an anomalous family dependent U(I)(X) symmetry. The latter is spontaneously br oken by non-zero vevs of a pair of singlet fields whose magnitude is determ ined through the D- and F-flatness conditions of the superpotential. We der ive the general solutions to the anomaly cancellation conditions and show t hat they allow numerous choices for the U(I), fermion charges which give se veral fermion mass textures in agreement with the observed fermion mass hie rarchy and mixing. Solutions with U(1)(X) fermion charge assignments are fo und which forbid or substantially suppress the dangerous baryon and lepton number violating operators and the lepton-Higgs mixing coupling while a Hig gs mixing mass parameter ( mu-term) can be fixed at the electroweak level. We give a general classification of the fermion mass textures with respect to the sum of the doublet-Higgs U(I), charges and show that suppression of dimension-five operators naturally occurs for various charge assignments. W e work out cases which retain a quartic term providing the left-handed neut rinos with Majorana masses in the absence of right-handed neutrino componen ts and consistent with the experimental bounds. Although there exist soluti ons which naturally combine all the above features with rather natural U(1) (X) charges, the suppression of the mu-term occurs for particular assignmen ts. (C) 2000 Elsevier Science B.V. All rights reserved.