Three-phonon vertex corrections to the excitation spectrum and liquid-structure function of liquid4He

The energy spectrum of elementary excitations and the liquid-structure function of liquid⁴He are calculated by means of the method of correlated basis functions in the approximation of second-order perturbation theory. The procedure is based on (i) the construction of phonon functions in terms of collective coordinates and the optimum Bijl-Dingle-Jastrow type of ground-state wave function and (ii) the evaluation of leading correction terms to the Bijl-Feynman excitation spectrum, which are generated by two types of three-phonon vertices. Numerical results are obtained using the optimum liquid-structure function computed by Campbell and Feenberg in the paired-phonon analysis.Research supported in part by the University of Kansas General Research Fund under grant No. 3235-5038.