Exact Monodromy Group of N=2 Heterotic Superstring

We describe an N = 2 heterotic superstring model of rank-3 which is dual to the type-II string compactified on a Calabi-Yau manifold with Betti numbers b 1,1 = 2 and b 1,2 = 86. We show that the exact duality symmetry found from the type II realization contains the per-turbative duality group of the heterotic model, as well as the exact quantum monodromies of the rigid SU(2) super-Yang-Mills theory. Moreover, it contains a non-perturbative mon-odromy which is stringy in origin and corresponds roughly to an exchange of the string 1 Laboratoire Propre du CNRS UPR A.0014.