HIGH-TEMPERATURE PHASE-TRANSITIONS WITHOUT INFRARED DIVERGENCES

The most commonly used method for the study of high temperature phase transitions is based on the perturbative evaluation of the temperature-dependent effective potential. This method becomes unreliable in the case of a second order or weakly first order phase transition, due to the appearance of infrared divergences. These divergences can be controlled through the method of the effective average action, which employs renormalization group ideas. We report on the study of the high temperature phase transition for the N-component phi4 theory. A detailed quantitative picture of the second order phase transition is presented, including the critical exponents for the behavior in the vicinity of the critical temperature. An independent check of the results is obtained in the large N limit, and contact with the perturbative approach is established through the study of the Schwinger-Dyson equations.