Strongly coupled compact lattice QED with staggered fermions

We explore the compact U(1) lattice gauge theory with staggered fermions and gauge field action − ∑ P [β cos(ΘP ) + γ cos(2ΘP )], both for dynamical fermions and in the quenched approximation. (ΘP denotes the plaquette angle.) In simulations with dynamical fermions at various γ ≤ −0.2 on 64 lattices we find the energy gap at the phase transition of a size comparable to the pure gauge theory for γ ≤ 0 on the same lattice, diminishing with decreasing γ. This suggests a second order transition in the thermodynamic limit of the theory with fermions for γ below some finite negative value. Studying the theory on large lattices at γ = −0.2 in the quenched approximation by means of the equation of state we find non-Gaussian values of the critical exponents associated with the chiral condensate, β ≃ 0.32 and δ ≃ 1.8, and determine the scaling function. Furthermore, we evaluate the meson spectrum and study the PCAC relation.