Density fluctuation spectrum of superfluidHe4at finite temperatures

Very recently, Woods and Svensson have reported neutron scattering experiments which indicate that the temperature-dependent weight of the elementary excitation resonance in superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is directly proportional to the superfluid density ${\rho }_s\mathrm{}\left(T\right)\mathrm{}$. We argue that this result can be easily understood within the general framework of the standard field-theoretic formulation of a Bose-condensed system and that it gives strong evidence in favor of the regularity hypothesis introduced by Hohenberg and Martin.