  We establish a general vector field model to describe the role of
transverse-momentum currents in the optical Magnus effect in free space. As an
analogy of the mechanical Magnus effect, the circularly polarized wave packet
in our model acts as the rotating ball, and its rotation direction depends on
the polarization state. Based on this model, we demonstrate the existence of an
optical polarization-dependent Magnus effect which is significantly different
from the conventional optical Magnus effect in that light-matter interaction is
not required. Further, we reveal the relation between transverse-momentum
currents and the optical Magnus effect, and find that such a
polarization-dependent rotation is unavoidable when the wave packet possesses
transverse-momentum currents. The physics underlying this intriguing effect is
the combined contributions of transverse spin and orbital currents. We predict
that this effect may be observed experimentally even in the propagation
direction. These findings provide further evidence for the optical Magnus
effect in free space and can be extrapolated to other physical systems.
