Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
1998-12-19
JHEP 9904 (1999) 002
Physics
High Energy Physics
High Energy Physics - Theory
45 pages, latex, eight eps figures (three in color)
Scientific paper
10.1088/1126-6708/1999/04/002
The O(n) nonlinear sigma model in 1+1 dimensions is examined as quantum mechanics on an infinite-dimensional configuration space. Two metrics are defined in this space. One of these metrics is the same as Feynman's distance, but we show his conclusions concerning potential energy versus distance from the classical vacuum are incorrect. The potential-energy functional is found to have barriers; the configurations on these barriers are solitons of an associated sigma model with an external source. The tunneling amplitude is computed for the O(2) model and soliton condensation is shown to drive the phase transition at a critical coupling. We find the tunneling paths in the configuration space of the O(3) model and argue that these are responsible for the mass gap at $\theta=0$. These tunneling paths have half-integer topological charge, supporting the conjecture due to Affleck and Haldane that there is a massless phase at $\theta=\pi$.
Moreno Esteban
Orland Peter
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