Theory of a degenerate Bose fluid. II

The theory developed in an earlier paper is applied to the degenerate Bose fluid at very low temperatures. It is seen that the transformation functions A(k), B(k), and C(k) can be chosen in such a way that the expansions of the grand potential and the momentum distribution are well behaved at very low temperatures. It is found that with this choice the Bogoliubov theory is an approximation to the first order results obtained with the present theory. The equilibrium properties of the system are calculated in second order and discussed. It is shown that, at least through second order, there is no energy gap at zero momentum in the quasiparticle energy spectrum. (Auth.)