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

We investigate the continuum limit of the gauge-ball spectrum in the four-dimensional pure U(1) lattice gauge theory. In the confinement phase we identify various states scaling with the correlation length exponent nu similar or equal to 0.35. The square root of the string tension also scales with this exponent, which agrees with the non-Gaussian fixed point exponent recently found in the finite-size studies of this theory, Possible scenarios for constructing a non-Gaussian continuum theory with the observed gauge-ball spectrum are discussed. The 0(++) state, however, scales with a Gaussian value nu similar or equal to 0.5. This suggests the existence of a second, Gaussian continuum limit in the confinement phase and also the presence of a light or possibly massless scalar in the non-Gaussian continuum theory. In the Coulomb phase we find evidence for a few gauge balls, being resonances in multi-photon channels; they seem to approach the continuum limit with as yet unknown critical exponents, The maximal value of the renormalized coupling in this phase is determined and its universality confirmed. (C) 1997 Elsevier Science B.V.