Würzburg Seminar on Quantum Field Theory and Gravity

After reviewing S-duality in 4d and mirror symmetry in 3d, I will discuss the dynamics of three-dimensional Maxwell theory coupled to a level- Chern-Simons term. 
Motivated by S-duality in string theory, I will argue that the theory admits an S-dual description. The S-dual theory contains a non gauge one-form field, previously proposed by Deser and Jackiw and a Chern-Simons term, . The couplings to external electric and magnetic currents and their string theory realizations will also be discussed.