Microscopic Calculations of the Dynamic Structure Factor of Bulk Liquid 4He

Results of many-body calculations of the dynamic structure factor of bulk liquid 4 He in 2D and 3D are presented and analyzed. The problem is reformulated as one of solving equations of motion for the one- and two-body correlations derived from a microscopic Hamiltonian and from a Jastrow-Feenberg wave function with time-dependent correlation functions through the least-action principle. At the first practical level of implementation this reproduces the correlated basis functions (CBF) theory, which gives qualitatively correct low-energy properties. The theory is used to study the anomalous dispersion of low-momentum phonons and the high-momentum behavior of the single-excitation branch near the two-roton continuum.