a Generic way to Look at Many-Body Theory

Based on ideas of density functional theory, we formulate a "generic" many-body theory. It is shown that the ground state configuration of a many-body system can be derived from a variational principle for the energy as a functional of thepair distribution function, and that such a variational principle is consistent with the Feynman-Hellman theorem. The functional is then constructed by postulating that the pair distribution function satisfies the two fundamental equations of many-body theory, namely the Bethe-Goldstone equation and the RPA equation, in a self-consistent manner. The generating energy functional of the theory is identical to the energy functional derived within the optimized HNC theory.