Unitary matrix models and phase transition

Abstract

We study the unitary matrix model with a topological term. We call the topological term the theta term. In the symmetric model there is the phase transition between the strong and weak coupling regime at λ c =2. If the Wilson term is bigger than the theta term, there is the strong-weak coupling phase transition at the same λ c . On the other hand, if the theta term is bigger than the Wilson term, there is only the strong coupling regime. So the topological phase transition disappears in this case.