ABSTRACT
This chapter focuses on "steady" superfluid flow, in which the superfluid velocity, vs, satisfies the equation div vs=0. Such flow can, in principle, occur only in multiply-connected systems. However, it is possible to achieve an equivalent situation in the bulk of the liquid by setting up vortex lines. The major new feature brought in by superfluidity, and a most important one indeed, is the quantization of vortex lines, arising as a consequence of the quantization of circulation. The square terms in correspond to the energy of the single vortex lines, while the cross term describes an interaction energy between two vortex lines. In the absence of vortex lines, the superfluid and normal components of a Bose liquid are completely decoupled. The velocity pattern of the vortex gives rise to a position-dependent energy, which may be used to calculate the scattering. The dynamics of superfluid flow is thus appreciably modified by the presence of vortex lines.
