Optimized delta expansion for relativistic nuclear models

The optimized $\delta$-expansion is a nonperturbative approach for field theoretic models which combines the techniques of perturbation theory and the variational principle. This technique is discussed in the $\lambda \phi^4$ model and then implemented in the Walecka model for the equation of state of nuclear matter. The results obtained with the $\delta$ expansion are compared with those obtained with the traditional mean field, relativistic Hartree and Hartree-Fock approximations.