Long-Wavelength Excitations in a Bose Gas And Liquid He II at T = 0
There are many assumptions that have been made, both in theoretical1 and experimental2 investigations, about the nature of the long-wavelength excitations of liquid He II. As an example, it is common to assume that the excitation spectrum ω(k) and various structure functions S(k) can be expanded in a power series in the wave vector k. A theoretical justification of the various assumptions is an important problem, but in the absence of a tractable microscopic theory of a strongly interacting Bose system we must look for other ways to test these assumptions. One way is by a qualitative analysis coupled with the use of plausible sum rule arguments. Another way is by a rigorous microscopic analysis of a solvable model of a Bose gas.
KeywordsBose System Density Response Function Dynamic Structure Function Elementary Excitation Spectrum Virtual Phonon
Unable to display preview. Download preview PDF.