Self-Dual Nonsupersymmetric Type II String Compactifications

It has recently been proposed that certain nonsupersymmetric type II orbifolds have vanishing perturbative contributions to the cosmological constant. We show that techniques of Sen and Vafa allow one to construct dual type II descriptions of these models (some of which have no weakly coupled heterotic dual). The dual type II models are given by the same orbifolds with the string coupling $S$ and a $T^2$ volume $T$ exchanged. This allows us to argue that in various strongly coupled limits of the original type II models, there are weakly coupled duals which exhibit the same perturbative cancellations as the original models.