Eigenvalues and Eigenfunctions of a Bose System of Hard Spheres and Its Low-Temperature Properties

It is shown that the pseudopotential method can be used for an explicit calculation of the first few terms in an expansion in power of ${\left(\rho a^3\right)}^{\frac{1}{2}}$ of the eigenvalues and the corresponding eigenfunctions of a system of Bose particles with hard-sphere interaction. The low-temperature properties of the system are discussed.