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Nonperturbative effects of a topological theta term on principal chiral nonlinear sigma models in 2 + 1 dimensions
Cenke Xu1, Andreas W W Ludwig1
1Department of Physics, University of California, Santa Barbara, California 93106, USA.
Abstract:
We study the effects of a topological Theta term on 2+1-dimensional principal chiral models, which are nonlinear sigma models defined on Lie group manifolds. We find that when Θ=π, the nature of the disordered phase of the principal chiral model is strongly affected by the topological term: it is either a gapless conformal field theory, or it is gapped and twofold degenerate. The result of our Letter can be used to analyze the boundary states of three-dimensional symmetry protected topological phases.
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