  It is shown that in a large class of systems plane waves can act as tractor
beams: i.e., an incident plane wave can exert a pulling force on the scatterer.
The underlying physical mechanism for the pulling force is due to the
sufficiently strong scattering of the incoming wave into another mode having a
larger wave number, in which case excess momentum is created behind the
scatterer. Such a tractor beam or negative radiation pressure effect arises
naturally in systems where the coupling between the scattering channels is due
to Aharonov-Bohm (AB) gauge potentials. It is demonstrated that this effect is
also present if the AB potential is an induced, ("artificial") gauge potential
such as the one found in J. March-Russell, J. Preskill, F. Wilczek, Phys. Rev.
Lett. 58 2567 (1992).
