CRITICAL PROPERTIES AND MONOPOLES IN U(1) LATTICE GAUGE-THEORY

We present a detailed study of the properties of the phase transition in the four-dimensional compact U(1) lattice gauge theory supplemented by a monopole term, for values of the monopole coupling lambda such t hat the transition is of second order. By a finite size analysis we sh ow that at lambda = 0.9 the critical exponent is already characteristi c of a second-order transition. Moreover, we find that this exponent i s definitely different from the one of the Gaussian case. We further o bserve that the monopole density becomes approximately constant in the second-order region. Finally we reveal the unexpected phenomenon that the phase transition persists up to very large values of lambda, wher e the transition moves to (large) negative beta.