Universality of the gauge-ball spectrum of the four-dimensional pure U(1) gauge theory

We continue numerical studies of the spectrum of the pure U(1) lattice gaug e theory in the confinement phase, initiated in Nucl. Phys. B 499 (1997) 37 1. Using the extended Wilson action S = -Sigma(P)[beta cos(Theta(P)) + gamm a cos(2 Theta(P))] we address the question of universality of the phase tra nsition line in the (beta,gamma) plane between the confinement and the Coul omb phases. Our present results at gamma = -0.5 for the gauge-ball spectrum are fully consistent with the previous results obtained at gamma = -0.2. A gain, two different correlation length exponents, nu(ng) = 0.35(2) and nu(g ) = 0.51(3), are obtained in different channels. We also confirm the stabil ity of the values of these exponents with respect to the variation of the d istance from the critical point at which they are determined. These results further demonstrate universal critical behaviour of the model at least up to correlation lengths of 4 lattice spacings when the phase transition is a pproached in some interval at gamma less than or equal to -0.2. (C) 1999 El sevier Science B.V.