TOROIDAL ORBIFOLD MODELS WITH A WESS-ZUMINO TERM

Closed bosonic string theory on toroidal orbifolds is studied in a Lag rangian path integral formulation. It is shown that a level one twiste d WZW action whose field value is restricted to Cartan subgroups of si mply-laced Lie groups on a Riemann surface is a natural and nontrivial extension of a first quantized action of string theory on orbifolds w ith an antisymmetric background field.