Dissipative dynamics of a kink state in a Bose-condensed gas

We develop a theory of dissipative dynamics of a kink state in a finite-temperature Bose-condensed gas. We find that, due to the interaction with the thermal cloud, the kink state accelerates towards the velocity of sound and continuously transforms to the ground-state condensate. We calculate the lifetime of a kink state in a trapped gas and discuss possible experimental implications.