Aspects of double string theory actions

In this thesis a manifestly T-duality invariant formulation of closed bosonic string theory is examined. The world-sheet action associated with this model depends explicitly on both the string coordinates and their T-duals, so doubling the number of dynamical variables along the compactified dimensions. The first order Lagrangians obtained describe constrained systems and require Dirac's quantization procedure. It results that the string coordinates and their duals behave like noncommuting variables. Nevertheless, once expressed in terms of Fourier modes, they give the same oscillator algebra as the one of the standard formulation.