The Dual Faces of String

Duality symmetries for strings moving in non-trivial spacetime backgrounds are analysed. It is shown that, for backgrounds generated from compact WZW and coset models, such duality symmetries are exact to all orders in string perturbation theory. A global treatment of duality symmetries is given, by associating them to the known symmetries of affine current algebras ( affine-Weyl group and external automorphisms). It is argued that self-duality symmetries of WZW and coset models generate the duality symmetries of their moduli space. Some remarks are presented, concerning the survival of such symmetries in the non-compact case. The implications of duality symmetries for string dynamics in non-trivial/singular spacetimes are discussed. CERN-TH.7012/93 September 1993 Talk presented at the ”Strings 93” Conference, May 1993, Berkeley. To appear in the Proceedings.