Improving the Lattice QED Action
  Strongly coupled QED is a model whose physics is dominated by short-ranged effects. In order to assess which features of numerical simulations of the chiral phase transition are universal and which are not, we have formulated a quenched version of the model in which photon degrees of freedom are defined on a lattice of spacing a, but fermions only on a lattice of spacing 2a. The fermi-photon interaction is then obtained via a blocking procedure, whose parameters allow a degree of control over the relative importance of short wavelength modes. Results from a variety of models are presented; the critical exponents delta and beta governing the transition appear to be independent of the blocking, or even of whether a gauge-invariant action is used for the photons. 
Simon Hands (University of Wales, Swansea)