2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/56336String theory compactified on a three-torus possesses an SL(5,Z) U-duality group. We investigate the realisation of this symmetry on the Born-Infeld theory on a three-brane, and discuss a U-duality covariant formulation of the BPS sector of the theory where the rank of the gauge group is treated on an equal footing with the fluxes.6 pages, talk presented at QFTHEP'99, Moscow, May 27 - June 2, 1999 and at the TMR-meeting `Quantum aspects of gauge theories, supersymmetry and unification', Paris ENS, September 1-7, 1999High Energy Physics - Theorytext