On the finite temperature λφ4 model. Is there a first order phase transition in (λφ4)3?

We investigate the behavior at finite temperature of the massive λ φ4 model in a D-dimensional spacetime, performing a renormalization up to the order of one loop. In this approximation we show that the thermal mass increase with the temperature, while the thermal coupling constant decrease with the temperature. We establish that in the (λφ4)3 model there is a temperature β*-1 above which the coupling constant becomes negative. We argue that the system could develop a first order phase transition, where the origin corresponds to a metastable vacuum. (author). 29 refs