Comment on anomalous dispersion and scattering rates for multiphonon spontaneous decay in He II.
01 January 1984
It is well known that the dispersion curve of liquid He II at the saturated vapor pressure is anomalous, i.e., the phase velocity has a maximum at finite wave vectors. As a consequence, the spontaneous decay of a high frequency phonon into lower frequency ones is prohibited above a certain threshold energy, E(c). A precise determination of E(c) should allow one to choose between various models of the dispersion curve for He II and shed light on the relevant multiphonon decay processes. In this paper we report on new measurements of E(c) at a temperature of 0.1K.