Hydrodynamic modes of H↓

Abstract
The normal modes of a nonuniform distribution of H↓ atoms are studied in the hydrodynamic regime. Explicit results for the eigenfrequencies, phase velocities, etc., are obtained under special conditions. The two-fluid equations for a uniform H↓ system are then analyzed to show that below the Bose-Einstein condensation temperature there are two modes involving strongly coupled pressure and temperature oscillations.