2-BODY DENSITY MATRIX OF BOSE FLUIDS

A detailed cluster analysis of the two-body density matrix n(r1, r2, r′1, r′2) and the associated pairing matrix elements is performed for a strongly interacting system of bosons described by a Jastrow wave function. The study employs a multiplicative cluster procedure as suggested by Feenberg. It is demonstrated that the density matrix has a structure f(r)f(r′)n(r)n(r′)exp[-R(r1, r2,r′1,r′2)] where f(r) is the conventional Jastrow factor and n(r) the one-body density matrix corresponding to the Jastrow trial state (r |r1-r2|, r′ |r′1-r′2|). The function R may be expressed by a series of irreducible cluster contributions which are given by a compact expressions in terms of spatial distribution functions. The density matrix exhibits off-diagonal long range order of the type n(r1, r2, r′1, r′2) → f(r)n(r)f(r′)n(r′) as |r1-r′1| → ∞,r,r′ < ∞. The associated pairing matrix elements and pairing energy of a Bose fluid are derived upon proper specialization of our results for the two-body density matrix. © 1979.