CRITICAL-TEMPERATURE AND AMPLITUDE RATIOS FROM A FINITE-TEMPERATURE RENORMALIZATION-GROUP

We study lambda phi(4) theory using an environmentally friendly finite temperature renormalization group. We derive flow equations, using a fiducial temperature as flow parameter, develop them perturbatively in an expansion free from ultraviolet and infrared divergences, then int egrate them numerically from zero to temperatures above the critical t emperature. The critical temperature, at which the mass vanishes, is o btained by integrating the flow equations, and is determined as a func tion of the aero temperature mass and coupling. We calculate the field expectation value and the minimum of the effective potential as funct ions of temperature and derive some universal amplitude ratios which c onnect the broken and symmetric phases of the theory. The latter are f ound to be in good agreement with those of the three-dimensional Ising model obtained from high and low temperature series expansions.