We construct an MSSM-like model from intersecting D-branes in Type IIA theory on the Z2 ×Z2 orientifold where the D-branes wrap rigid 3-cycles. Because the 3-cycles are rigid, there are no extra massless fields in the adjoint representation, arising as open-string moduli. The presence of these unobserved fields would create difficulties with asymptotic freedom as well as the prediction of gauge...

In family unification models, all three families of quarks and leptons are grouped together into an irreducible representation of a simple gauge group, thus unifying the Standard Model gauge symmetries and a gauged family symmetry. Large orthogonal groups, and the exceptional groups E7 and E8 have been much studied for family unification. The main theoretical difficulty of family unification is...

We examine the low energy structure of N = 1 supersymmetric SO(10) gauge theory with matter chiral superfields in NQ spinor and Nf vector representations. We construct a dual to this model based upon an SU(Nf + 2NQ − 7)×Sp(2NQ − 2) gauge group without utilizing deconfinement methods. This product theory generalizes all previously known Pouliot-type duals to SO(Nc) models with spinor and vector ...

We study the mass spectrum of superparticles within supersymmetric grand unified models. For gaugino masses, it is pointed out that the GUT-relation in the SU(5) model is applicable to a more general case where a grand-unified gauge group breaks down to the standard model gauge group by several steps. We also show that the mass spectrum of squarks and sleptons carries the information on the bre...

A five-dimensional SU(5) grand unified theory is constructed on the orbifold S/Z2, with gauge symmetry breaking accomplished by a background gauge field. The theory is shown to be equivalent to one with gauge symmetry breaking by orbifold boundary conditions — the two pictures are related by a non-periodic gauge transformation. This effective field theory possesses localized explicit breaking o...

We construct a supersymmetric grand unified model in the framework of a latticized extra dimension. The SU(5) symmetries on the lattice are broken by the vacuum expectation values of the link fields connecting adjacent SU(5) sites, leaving just the MSSM at low energies. Below the SU(5) breaking scale, the theory gives rise to a similar spectrum as in orbifold breaking of SU(5) symmetry in 5 dim...

In 1954, Yang and Mills founded the non-Abel gauge field theory [1 ]. Since then, the gauge field theory has developed greatly, and has been widely applied to elementary particle theory. Now, we believe that, four kinds of fundamental interactions in nature are all gauge interactions and can be described by gauge field theories. It is generally believed that the principle of local gauge invaria...

The recent LEP data for gauge coupling constants constrain many grand unified models. In this paper, we study several possibilities for unification of gauge coupling constants. Without an intermediate scale, the minimal supersymmetric standard model with two Higgs doublets is the only possibility. For one intermediate scale, we present a few unification schemes without supersymmetry. One of the...