Supersymmetric grand unification model with the orbifold symmetry breaking in the six-dimensional supergravity

We construct supersymmetric (SUSY) grand unification (GUT) models in the six-dimensional space–time where the GUT symmetry is broken down to the standard-model gauge group by a simple orbifolding T2/Z4 or T2/Z6 and a pair of massless Higgs doublets in the SUSY standard model are naturally obtained. Since the background geometry here is simple compared with models using the Scherk–Schwarz mechanism, one might hope for an approximate gauge coupling unification in the present models. Here, the presence of the massless Higgs multiplets in the bulk is quite natural, since the anomaly cancellation in the six-dimensional space–time requires N=2 hyper multiplets in the bulk, some of which are origins of the Higgs doublets. However, the origin of the quarks and leptons is still not clear at all.