Roton liquid theory

A mean field approach, analogous to the Landau theory of Fermi liquids, is developed and applied to the interacting roton liquid present in superfluid /sup 4/He at the temperatures below the lambda-point. We derive stability conditions for the parameters describing the effective roton-roton interaction and use one of these to place a bound on the variation with temperature of the roton energy. By fitting to experimental results on the specific heat and normal fluid density, we obtain the first two moments of the effective roton interaction.