GAUSSIAN EFFECTIVE POTENTIAL IN VARIATIONAL PERTURBATION-THEORY

The nonperturbative Gaussian effective potential is derived in the lam bdaphi4-theory as the first nontrivial order of variational perturbati on theory. In the framework of the proposed approach the algorithm of calculating corrections is determined from the very beginning. Various ways of constructing the variational procedure for the action functio nal and questions about the convergence of the variational perturbatio n theory series are discussed. The series convergence for the anharmon ic variational perturbation theory functional is proved.