A study of the phase transition in 4D pure compact U(1) LGT on toroidal   and spherical lattices
  We have performed a systematic study of the phase transition in the pure compact U(1) lattice gauge theory in the extended coupling parameter space (\beta, \gamma) on toroidal and spherical lattices. The observation of a non-zero latent heat in both topologies for all investigated \gamma in the interval [+0.2,-0.4], together with an effective exponent \nu = 1/d when large enough lattices are considered, lead us to conclude that the phase transition is first order. For negative \gamma, our results point to an increasingly weak first order transition as \gamma is made more negative. 
Isabel Campos, Andres Cruz and Alfonso Tarancon