ABSTRACT
The beginning of the spectrum is, to a first approximation, linear and represents phonons. However for a certain number of phenomena the dispersion of the phonon part of the spectrum—that is, its departure from a linear dependence, turns out to be of importance. Since this effect is extremely small, it is impossible to determine its magnitude from existing neutron scattering data. It is also not clear whether it can be calculated theoretically by considering a system of interacting phonons. However since the phonon spectrum is stable and the liquid isotropic, one may immediately write down for the initial part of the phonon spectrum the expression () ϵ = cp ( 1 − γ p 2 ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429502897/20d72e0b-9d39-4175-acc6-a943547edf8a/content/eq175.tif"/>
