Ground State of a Bose System of Hard Spheres

It is shown that the pseudopotential method can be extended to yield further terms in the low-density expansion of the ground-state energy of a system of Boltzmann or Bose particles with hard-sphere interaction. Two terms beyond the known result are found, and the expansion is no longer a power series in ${\left(a^3\rho \right)}^{\frac{1}{2}}$. Other related properties of the system are discussed.