2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/186698We 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 $\SU6$ gauge symmetry in the bulk and two pairs of inequivalent fixed points with unbroken $\SU5$ and $\SU2 \times \SU4$ symmetry, respectively. All anomalies are cancelled by the Green-Schwarz mechanism. Two quark-lepton generations are located at the $\SU5$ 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 $\SU5$ mass relations.Talk given at 13th International Symposium on Particles, Strings and Cosmology (PASCOS 07), London, England, 2-7 Jul 2007High Energy Physics - Theorytext