One-particle density matrix of liquid $^4\text{He}$

Using the expression for the total density matrix for a system of $N$ interacting Bose particles found in our previous papers, we calculate the one-particle density matrix in the coordinate representation. At low temperatures, the leading approximation of this matrix reproduces the results of the Bogoliubov theory. In the classical limit, the proposed theory reproduces the results of the theory of the classical liquid in the approximation of chaotic phases. From the one-particle density matrix, we find the particle momentum distribution function and the mean kinetic energy of the Bose liquid and investigate the phenomenon of Bose–Einstein condensation.