HIERARCHICAL FERMION MASSES AND MIXING ANGLES FROM THE FLIPPED STRING

We present a general method to obtain specific predictions for the fermion masses and mixings in the low-energy theory of the flipped SU(5) × U(1) superstring model. The condition of unbroken N = 1 supergravity at MPl in the presence of an anomalous UA(1) symmetry gives strong constraints on the parameters of the model. We obtain: (i) a top quark mass between 60 and 100 GeV, with values close to 100 GeV strongly favored; (ii) up- and down-type quark and lepton mass ratios and Cabibbo-Kobayashi-Maskawa mixings, which could be found consistent with their accepted values simultaneously in parameter space; (iii) a direct connection between the hierarchical fermion mass spectrum and baryon decay modes, we find p → μ+π0, νμπ+; n → μ+π-, νμπ0, with τp ∼ τn ∼ 1035±2y; and (iv) a vanishing bare u quark mass that solves the strong CP problem in this model and is not in conflict with previous expectations. We stress that a full dynamical calculation would unambigously determine these observables and hence constitute a definite test of the model. However, the whole framework is so constrained that crucial information can already be extracted from the model at this stage. © 1980.