Hartree-Fock Theory and the Λ Transformation in Quantum Statistical Mechanics. II. Degenerate Bose System
In a previous paper, a Hartree-Fock theory of the quantum Ursell expansion for Fermi fluids was developed. The same techniques are used in this paper to derive a theory of degenerate Bose fluids from the x-ensemble theory of Lee and Yang. It is shown that this theory is equivalent to the Λ-transformed theory recently derived by Mohling, RamaRao, and Shea. The present approach considerably simplifies the formalism and eliminates the need for the Λ transformation. By working entirely in a quasiparticle framework, we also avoid the problems with unphysical line factors which have appeared in earlier theories. Finally, a greatly simplified Λ transformation is obtained for use in problems in which the potential contains an infinitely repulsive core.