They propose to measure the linewidth of phonons in the lattice phase of electrons on the surface of liquid helium to check the weak coupling theory of longitudinal phonon linewidths. This theory predicts the linewidths to vary inversely with the phonon frequency, and predicts the density and temperature dependence of the linewidth. A maximum in the linewidth is predicted at about one-tenth the melting temperature. This results from a reduction in scattering at high temperatures due to the Debye-Waller factor. The weak coupling approximation is expected to hold for densities below 107/cm. Their measurements should check the range of validity of this theory.
