GAUSSIAN EFFECTIVE POTENTIAL IN VARIATIONAL PERTURBATION-THEORY

The nonperturbative Gaussian effective potential is derived in the lambdaphi4-theory as the first nontrivial order of variational perturbation 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 functional and questions about the convergence of the variational perturbation theory series are discussed. The series convergence for the anharmonic variational perturbation theory functional is proved.