Zero-Temperature Properties of the Many-Fermion System

It is shown that the class of correlation graphs which arise in the calculation of thermodynamic properties in the canonical ensemble can be summed to give renormalized single-particle populations. In the limit of zero temperature the perturbation expansion of the energy then reduces to the adiabatic expansion of Goldstone about the correct model state. Arguments for the consistency of the expansion are developed for the case of the nonspherical Fermi surface.