Gapless Hartree-Fock Resummation Scheme for the O(N) Model

Abstract

A modified selfconsistent Hartree-Fock approximation to the lambda*phi^4 theory with spontaneously broken O(N) symmetry is proposed. It preserves all the desirable features, like conservation laws and thermodynamic consistency, of the selfconsistent Dyson scheme generated from a 2PI functional, also known as the Phi-derivable scheme, while simultaneously respecting the Nambu-Goldstone theorem in the chiral-symmetry broken phase. Various approximate resummation schemes are discussed.

Comments: 13 pages, 10 figures / Version accepted by Phys. Rev. D: the introduction has been expanded by a few remarks in order to further clarify the goal of the paper