2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55086We describe an approach to understanding exponential decay of correlation functions in asymptotically free theories. This approach is systematic; it does not start from any conjectured mechanism or picture. We begin by studying the metric on the space of configurations and the behavior of the potential-energy function on this space. We describe how these ideas fit in the framework of QCD, as discussed earlier by one of us (P.O.). We then consider the 1+1-dimensional O(2) and O(3) nonlinear sigma models and show that no gap exists in the former at weak coupling. In the O(3) model a new kind of strong/weak-coupling duality is realized. We briefly outline our proposals for understanding the spectrum.15 pages, latex2e, three figures, uses plenum.sty Invited talk by P. Orland at the NATO Advanced Workshop, ``New Developments in Quantum Field Theory", Zakopane, Poland, June 14-19, 1997, proceedings to be published by Plenum PressHigh Energy Physics - Theorytext