PHASE-STRUCTURE AND MONOPOLES IN U(1) GAUGE-THEORY

We investigate the phase structure of pure compact U(1) lattice gauge theory in four dimensions with the Wilson action supplemented by a monopole term. To overcome the suppression of transitions between the phase in the simulations we make the monopole coupling a dynamical variable. We determine the phase diagram and find that the strength of the first-order transition decreases with the increasing weight of the monopole term, the transition thus ultimately reaching second order. After outlining the appropriate topological characterization of networks of currents lines, we present an analysis of the occurring monopole currents which shows that the phases are related to topological properties. © 1994 The American Physical Society.