N=2 supersymmetric theories, dyonic charges and instantons

Abstract

In the first part of this thesis we give an introduction to electric-magnetic duality and N=2 supersymmetry. After that we describe type II string theory instantons in the supergravity approximation. These instantons correspond to D-branes and NS-fivebranes wrapping non-vanishing cycles in the internal Calabi-Yau manifold. In the last chapter, we construct N=2 supersymmetric gauge theories involving both electric and magnetic (dyonic) charges. In these systems the electric-magnetic duality structure of the ungauged theories is preserved.