Energy of the Many-Fermion Normal System

Abstract

Perturbation theoretic equations for several properties of the zero- temperature many-fermion normal system are rederived from general considerations. Though none of the equations are new, some of the derivations are, and taken together they form a brief and simple summary of manyfermion relations and a basis for further investigation of the basic perturbation description of thc many- fermion normal system: the Brueckner-Goldstone expansion. A change-of-parameter technique is then developed and employed to investigate the possible use of the true momentum density instead of the unperturbed fermi distribution in the Brueckner-Goldstone expansion and in the Brueckner Kmatrix approximation. The result is a simpler, approximate perturbation series for the interaction energy, whose accuracy for nuclear matter is estimated to be approximately plus or minus 2 Mev. The new approximation is exact to the fourth order. (auth)