  We consider associated production of dark matter with single top quark, in a
simplified dark matter model with spin-0 mediators. The produced top quark is
polarized and the polarization depends on the CP of the mediator. We calculate
both the cross-section and top polarization for these processes. We compute
angular asymmetries which demonstrate the difference between the polarization
expected for the scalar or pseudoscalar mediator. Both the cross section and
top polarization are sensitive to the CP property of the mediator, depending on
the mediator mass. We find that these polarization asymmetries add value to the
determination of the CP property of the mediator particularly in the case of a
state with indeterminate CP.
