Theory of a degenerate Bose fluid. I

The x-ensemble formulation of Lee and Yang is used as the basis for a theory of the degenerate Bose fluid. The expansions of the grand potential and the momentum distribution are rearranged through a set of simple transformations; the transformed expansions no longer contain free particle energies and distribution functions, and are well behaved at low temperatures. Instead, characteristic quasiparticle energies and distribution functions appear. The quasi-particle energy is seen to be phonon-like at low momenta and particle-like at high momenta. As the macroscopic occupation of the zero momentum state vanishes, the theory reduces to the usual theory of a normal Bose fluid. (Auth.)