Causality and CPT violation from an Abelian Chern–Simons-like term Original Research Article

We study a class of generalized Abelian gauge field theories where CPT symmetry is violated by a Chern–Simons-like term which selects a preferred direction in spacetime. Such Chern–Simons-like terms may either emerge as part of the low-energy effective action of a more fundamental theory or be produced by chiral anomalies over a nonsimply connected spacetime manifold. Specifically, we investigate the issues of unitarity and causality. We find that the behaviour of these gauge field theories depends on whether the preferred direction is spacelike or timelike. For a purely spacelike preferred direction, a well-behaved Feynman propagator exists and microcausality holds, which indicates the possibility of a consistent quantization of the theory. For timelike preferred directions, unitarity or causality is violated and a consistent quantization does not seem to be possible.