ANALYTICAL METHOD IN LATTICE GAUGE THEORY AT FINITE TEMPERATURE

A variational-cumulant expansion method at finite temperature is developed in the lattice gauge theory. The order parameter < L > (the statistical average of the thermal loop) is analytically calculated to the 3rd order cumulant expansion. The change of < L > = 0 to < L > ≠ 0 clearly shows the existence of a deconfine phase transition of 2nd order in agreement with the latest Monte Carlo simulations.