STRINGS FROM ORIENTIFOLDS

We construct models in 1+1 dimensions with chiral (0, N) supersymmetry by taking orientifolds of type IIB on an eight-torus identified by di fferent numbers of reflections. The resulting models have Dirichlet st rings, 5-branes and 9-branes stretched along different directions. The cases we study in detail have residual chiral supersymmetry (0, 8), ( 0,4) and (0, 2). The gravitational anomaly in all cases is shown to ca ncel. (C) 1998 Elsevier Science B.V.