  We consider half-integer topological defects in a spinor Bose-Einstein
condensate of exciton-polaritons. We show that they accelerate under the effect
of an in-plane effective magnetic field, like regular electric charges in the
electric field. The trajectories of these analogues of magnetic monopoles are
derived analytically and checked by numerical simulations. We show that these
"magnetic charges" propagate at large in-plane velocities and remain stable up
to a critical magnetic field, thanks to the unique spin-anisotropy of polariton
interactions.
