Flavor Symmetry in Gauge-Higgs-Matter Unified Orbifold GUTs

We construct an orbifold model in which all the standard model particles are unified in a gauge multiplet in higher dimensional supersymmetric gauge theory. We find that a flavor symmetry has to remain in four dimensions due to the discrete charge conservation for orbifold conditions if the colored Higgs components in the gauge multiplet are projected out. When the flavor symmetry originates from the E_8 bulk gauge symmetry, the successful unification model can be constructed. In the model, all the Dirac Yukawa couplings for quarks and leptons are generated by the higher dimensional gauge interaction.