Perturbation theory for quantum fluids at high temperature

A perturbation series is obtained which expresses the pressure, Ursell functions and distribution functions of a quantum fluid in terms of those of the unperturbed fluid having the same temperature and fugacity. The pair interaction potential of the unperturbed fluid is a non-analytic function of the interparticle separation. The advantage of this theory over the usual constant-density theory is that the general term of each series can be given. It is the integral of a product involving generalised Ursell functions of the unperturbed fluid and modified Ursell functions of the quantum fluid and can be conveniently represented by a graph. When this theory is applied to check the results obtained by the constant-density theory, it is found that the first quantum correction to the radial distribution function of the unperturbed fluid obtained by the latter theory needs modification.