Phenomenological implications of the flipped SU(5) × U(1) superstring model

TLDR: In this article, the authors studied the SU(5)×U(1)1.1.4×U (1)4×SO (10)×SO(6) superstring model and showed that the model describes two massive generations of quarks and leptons as well as a massless generation expected to receive naturally suppressed masses from higher order nonrenormalizable terms.

Abstract: We study in detail gauge symmetry breaking in the SU(5)×U(1)1×U(1)4×SO(10)×SO(6) superstring model, solving the D and F-flatness conditions and taking into account quartic and quintic superpotential terms. We find that, to this order, the model describes two massive generations of quarks and leptons as well as a massless generation expected to receive naturally suppressed masses from higher order non-renormalizable terms. D and F-flatness restricts the number of massless isodoublets to four. We solve the coupled renormalization group equations for the gauge and Yukawa couplings in the two-loop approximation and obtain the top-quark mass as a function of two parameters of the model which could be chosen to be ratios of singlet v.e.v's associated with the surplu s (U(1))4 breaking. We obtain a heavy top-quark with 150GeV ≤ m1