  We discuss a schematic model of mode-coupling theory for force-driven active
nonlinear microrheology, where a single probe particle is pulled by a constant
external force through a dense host medium. The model exhibits both a glass
transition for the host, and a force-induced delocalization transition, where
an initially localized probe inside the glassy host attains a nonvanishing
steady-state velocity by locally melting the glass. Asymptotic expressions for
the transient density correlation functions of the schematic model are derived,
valid close to the transition points. There appear several nontrivial time
scales relevant for the decay laws of the correlators. For the nonlinear
friction coeffcient of the probe, the asymptotic expressions cause various
regimes of power-law variation with the external force, and two-parameter
scaling laws.
