  In this work we present a transport model for the paraxial propagation of
vector beams. Of particular importance is the appearance of a new transverse
momentum term proportional to the linear polarization angle gradient imparted
to the beam during the beam preparation process. The model predicts that during
propagation, this new momentum will be exchanged for classical transverse
momentum, thereby causing the beam to accelerate. We observe the momentum
exchange in experiment by designing the polarization profile in such a way as
to cause the beam centroid to follow a parabolic path through free space.
