Tricritical point in compact U(1) lattice gauge theory with dynamical fermions

The compact U(1) lattice gauge theory with dynamical fermions of mass m = 0.1 and 0.05 with the gauge action ε/sub P/(BetacosΘ/sub P/+ γcos2θ/sub P/) is studied numerically along phase-transition lines in the β,γ plane. On a 84 lattice, discontinuities appearing in the internal energy and in the chiral order parameter at γ = 0 are shown to vanish as γ decreases to negative values, indicating a existence of tricritical points. These results are compared with high-statistics data of the internal energy in the pure gauge theory on a 164 lattice