Effects of dynamical Wilson fermions and the phase structure of compact QED₄

By comparison of the quenched and full formulations of compact QED with Wilson fermions we single out the effects of dynamical fermions on the `chiral transition line' within the confinement phase. It is shown that this line cannot correspond to the chiral limit of the theory for all values of the gauge coupling. This seems to imply the existence of tri-critical points in this theory, the phase structure of which has a close similarity to QCD at finite temperature.