Non-Gaussian fixed point in four-dimensional pure compact U(1) gauge theory on the lattice

The line of phase transitions separating the confinement phase from the Coulomb phase in the four-dimensional pure compact U(1) gauge theory with extended Wilson action is reconsidered. By means of a high precision simulation on spherical lattices and a finite-size scaling analysis we find that along a part of this line, including the Wilson action the critical scaling behavior is determined by one fixed point with non-Gaussian critical exponent nu = 0.365(8). This indicates the existence of a nontrivial and nonasymptotically free continuum limit of this theory, as well as of its dual equivalent.