Excitations in normal liquid ³He

Abstract

The dynamical density and spin-density response functions are expressed within a dispersion-relation representation in terms of the corresponding static susceptibilities and relaxation kernels. The kernels are approximated by two-mode decay processes. The resulting coupled integral equations are solved to get self-consistent spectral functions of the density and spin-density response. It is found that a density mode can decay into two density modes and two spin-fluctuation excitations whereas a spin-density fluctuation decays only into a density mode and a spin-density excitation. The theory predicts a well-defined zero-sound mode. The calculated excitation spectra of zero sound and spin-fluctuation excitations and their strengths are compared with neutron-scattering results.