Iordanskii force and the gravitational Aharonov-Bohm effect for a moving vortex

I discuss the scattering of phonons by a vortex moving with respect to a superfluid condensate. This allows us to test the compatibility of the scattering-theory derivation of the Iordanskii force with the Galilean invariance of the underlying fluid dynamics. In order to obtain the correct result we must retain ${O(v}_s^2)$ terms in the sound-wave equation, and this reinforces the interpretation, due to Volovik, of the Iordanskii force as an analogue of the gravitational Bohm-Aharonov effect.