SPURIOUS 1ST-ORDER PHASE-TRANSITIONS FROM TOPOLOGICAL EFFECTS ON THE LATTICE

The discrete nature of the topological charge, Q, leads to sudden jumps in observables when Q changes by +/- 1 in lattice gauge theory Monte Carlo simulations. This is especially apparent for couplings for which Q = 0 and Q = +/- 1 are the dominant configurations for the lattice being studied. Metastability of gauge configurations responsible for topological charge, and the strong dependence of quantities such as <psi-psi-BAR> on Q leads to behavior that has very much the appearance of a first-order chiral phase transition. However, this is only a result of topological charge quantization, the effects of which disappear in the infinite-lattice limit, and not a true phase transition. The phenomenon is demonstrated with Monte Carlo simulations of two-dimensional U(1) lattice gauge theory. The possibility that some signals attributed to first-order chiral transitions in four-dimensional theories could be due to this effect is discussed.