A lattice model with a theta term in three dimensions

We study a three-dimensional abelian lattice model in which the analogue of a theta term can be defined. This term is defined by introducing a neutral scalar field and its effect is to couple magnetic monopoles to the scalar field and vortices to the gauge field. An interesting feature of this model is the presence of an exact duality symmetry that acts on a three parameter space. It is shown that this model has an interesting phase structure for non-zero values of theta. In addition to the usual confinement and vortex phases there are phases in which loops with composite charges condense. The presence of novel point like excitations also alters the physical properties of the system.