Finite size analysis of the U(1) background field effective action

We apply the finite size scaling analysis to the derivative of the density of the effective action for the lattice U(1) pure gauge theory in an external constant magnetic field. We found evidence of a continuous phase transition. Our estimate of the critical parameters gives support to a recent claim of a non-Gaussian fixed point in four-dimensional compact U(1) gauge theory on the lattice. (C) 1997 Published by Elsevier Science B.V