Abstract :
We use the crosscap constraint to construct open descendants of the 0B string compactified on T6/Z3 and on T4/Z2 free of tachyons both in the closed and in the open unoriented sectors. In four dimensions the construction results in a Chan-Paton gauge group U(8)⊗U(12)⊗U(12) with three generations of chiral fermions in the representations (8,1,12)⊕(8,12,1)⊕(1,66,1)⊕(1,1,66).
