  A Keldysh-contour effective field theory is derived for magnetic vortices in
the presence of current flow. The effect of adiabatic and non-adiabatic spin
transfer torques on vortex motion is highlighted. Similarities to and
differences from the superconducting case are presented and explained. Current
flow across a magnetically ordered state is shown to lead to a defect-unbinding
phase transition which is intrinsically nonequilibrium in the sense of not
being driven by a variation in effective temperature. The dependence of the
density of vortices on the current density is determined.
