  It has been known since the pioneering work of Onsager and Feynman that the
statistical mechanics and dynamics of vortices play an essential role in the
behavior of superfluids and superconductors. However, the theory of vortices in
quantum fluids remains in a most unsatisfactory state, with many conflicting
results in the literature. In this paper we review the theory of Thouless, Ao
and Niu, which gives an expression for the total transverse force acting on a
quantized vortex that is in apparent disagreement with the work of Iordanskii
and of Lifshitz and Pitaevskii. In particular, no transverse force proportional
to the asymptotic normal fluid velocity was found. We use two-fluid
hydrodynamics to study this discrepancy.
