No abstract

T-DUALITYA perturbative symmetry of string theory that relates large and small distances in the spacetime. In toroidal compactifications it is realized aswhere R is the compactification radius and a 0 the inverse of the string tension, with the coupling constant transforming as [3] g ! g ffiffiffiffi a 0 p =R: This spacetime transformation is accompanied by the interchange between momentum and winding states of closed strings. It relates the two Type II ten dimensional superstring theories [4,5], as well as the two heterotic theories, with gauge groups SO(32) and E 8 Â E 8 [6]. T-duality of open strings gives rise to D-branes (nonperturbative extended objects charged with respect to the Ramond Ramond fields of the closed string spectrum) [5], which play an essential role in the string unification conjecture within (eleven dimensional) M-theory.