High temperature resummation in the linear delta expansion - art. no. 105005

The optimized linear delta expansion is applied to the lambda phi(4) theory at high temperature. Using the imaginary time formalism the thermal mass i s evaluated perturbatively up to order delta(2). A variational procedure as sociated with the method generates nonperturbative results which are used t o obtain the critical temperature for the phase transition. Our results are compared with the ones given by propagator dressing methods. [S0556-2821(9 9)03518-3].