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 εP({B}cosΘP+ {γ}cos2θP) 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 〈{ψ}{}{ψ}〉 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.