Variational theory of the acoustic impedance of normalHe3

A variational theory of the acoustic impedance of normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is developed within the framework of Landau's theory of Fermi liquids. Expressions are derived for both the longitudinal and transverse impedance using plane-wave trial functions. These expressions are simple and explicitly exhibit the analytical dependence of the impedance on the relevant Landau parameters. They are also accurate with errors less than 1% when compared with exact numerical calculations for physically reasonable values of the parameters.