Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2001-11-13
Phys.Lett. B529 (2002) 261-264
Physics
High Energy Physics
High Energy Physics - Theory
6 pages; v2: a couple of clarifying sentences added; v3: references added
Scientific paper
10.1016/S0370-2693(02)01261-3
The dependence on the topological theta angle term in quantum field theory is usually discussed in the context of instanton calculus. There the observables are 2 pi periodic, analytic functions of theta. However, in strongly coupled theories, the semi-classical instanton approximation can break down due to infrared divergences. Instances are indeed known where analyticity in theta can be lost, while the 2 pi periodicity is preserved. In this short note we exhibit a simple two dimensional example where the 2 pi periodicity is lost. The observables remain periodic under the transformation theta -> theta + 2 k pi for some k >= 2. We also briefly discuss the case of four dimensional N=2 supersymmetric gauge theories.
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