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

Abstract

The compact U(1) lattice gauge theory with dynamical fermions of mass m=0.1 and 0.05 with the gauge action ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{P}}$(\ensuremath{\mathrm{B}}cos${\mathrm{\ensuremath{\Theta}}}_{\mathit{P}}$+ \ensuremath{\gamma}cos2${\mathrm{\ensuremath{\theta}}}_{\mathit{P}}$) is studied numerically along phase-transition lines in the \ensuremath{\beta},\ensuremath{\gamma} plane. On a ${8}^{4}$ lattice, discontinuities appearing in the internal energy and in the chiral order parameter 〈\ensuremath{\psi}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\psi}〉 at \ensuremath{\gamma}=0 are shown to vanish as \ensuremath{\gamma} 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 ${16}^{4}$ lattice.