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)⊗SO(20) or SO(8)4⊗SO(4)3.