Supersymmetry and Dualities in Various Dimensions

Abstract

Since the seventies string theory has been discussed as a possible candidate for a theory which unifies all known particle interactions including gravity. Until recently, however, string theory has only been known in its perturbative regime. That is, the (particle) excitations of a string theory are computed in the free theory (g s = 0), while their scattering processes are evaluated in a perturbative series for g s ≪ 1. The string coupling constant g s is a free parameter of string theory but for g s O(1) no method of computing the spectrum or the interactions had been known. This situation dramatically changed during the past three years. For the first time it became possible to go beyond the purely perturbative regime and to reliably compute some of the nonperturbative properties of string theory. The central point of these developments rests on the idea that the strong-coupling limit of a given string theory can be described in terms of another, weakly coupled, ‘dual theory’. This dual theory can take the form of either a different string theory, or the same string theory with a different set of perturbative excitations, or a new theory termed M-theory.