Spectra of 4D, N=1 Type I String Vacua on Non-Toroidal CY Threefolds
  We compute the massless spectra of some four dimensional, N=1 supersymmetric compactifications of the type I string. The backgrounds are non-toroidal Calabi-Yau manifolds described at special points in moduli space by Gepner models. Surprisingly, the abstract conformal field theory computation reveals Chan-Paton gauge groups as big as SO(12) x SO(20) or SO(8)^4 x SO(4)^3. 
Ralph Blumenhagen and Andreas Wisskirchen