The flipped SU(5)×U(1) string model revamped

Abstract

We present a refined version of our three-generation flipped ,SU(5)×U(1) string model with the following properties. • -The complete massless spectrum is derived and shown to be free of all gauge and mixed anomalies apart from a single anomalous U(1). • -The imaginary part of the dilaton supermultiplet is eaten by the anomalous U(1) gauge boson, and the corresponding D-term is cancelled by large VEVs for singlet fields that break surplus U(1) gauge factors, leaving a supersymmetric vacuum with an SU(5)×U(1) visible gauge group and an SO(10)×SO(6) hidden gauge group. • -There are sufficient Higgs multiplets to break the visible gauge symmetry down to the standard model in an essentially unique way. • -All trilinear superpotential couplings have been calculated and there are in particular some giving m t , m b , m τ ≠0. • -A renormalization group analysis shows that m t <190 GeV and m b ≅3 m τ . • -Light Higgs doublets are split automatically from heavy Higgs triplets, leaving no residual dimension-five operators for baryon decay, and the baryon lifetime τ B ∼ 2×10 34±2 yr. • -There are no tree-level flavour-changing neutral currents, but μ→ eγ may occur at a detectable level: B( μ→ eγ) ∼ 10 −11 −10 −14.