Gauge-Higgs Unification from the Heterotic String

We present a 6D orbifold model on T 2/Z2 which emerges as intermediate step in the compactification of the heterotic string to the supersymmetric standard model in four dimensions. It has SU(6) gauge symmetry in the bulk and two pairs of inequivalent fixed points with unbroken SU(5) and SU(2)× SU(4) symmetry, respectively. All anomalies are cancelled by the GreenSchwarz mechanism. Two quark-lepton generations are located at the SU(5) branes, the third family is composed of split bulk hypermultiplets. The model has vacua with partial or full gauge-Higgs unification and non-vanishing Yukawa couplings which generically avoid the unsuccessful SU(5) mass relations.