MODULAR-GROUPS FOR TWISTED NARAIN MODELS

We demonstrate how to find modular discrete symmetry groups for Z(N) o rbifolds. The Z7 orbifold is treated in detail as a nontrivial example of a (2,2) orbifold model. We give the generators of the modular grou p for this case which, surprisingly, does not contain SL(2;Z)3 as had been speculated. The treatment models with discrete Wilson lines are a lso discussed. We consider examples which demonstrate that discrete Wi lson lines affect the modular group in a nontrivial manner. In particu lar, we show that it is possible for a Wilson line to break SL(2,Z).