New effects in the interaction of second sound with superfluid vortex lines

The force terms in the wave equation for second sound which arise from the interaction of rotons and vortex lines are recalculated. When the phase of the perturbation in the roton drift velocity owing to dragging of the rotons by the vortex lines is taken into account, new force terms are found. One of these terms predicts a decrease of the second-sound velocity proportional to the vortex density, in agreement with recent experiments on rotating helium and heat currents. The other term predicts a new contribution to the attenuation of second sound in rotating helium which may be observable.