Non-Abelian Brane Worlds: The Open String Story
  We extend the string model building rules for the construction of chiral supersymmetric Type I compactifications on smooth Calabi-Yau manifolds. These models contain stacks of D9-branes endowed with general stable U(n) bundles on their world-volume and D5-branes wrapping holomorphic curves on the Calabi-Yau. 
Ralph Blumenhagen, Gabriele Honecker, Timo Weigand