  The slow dynamics in a glassy hard-sphere system is dominated by cage
breaking events, i.e., rearrangements where a particle escapes from the cage
formed by its neighboring particles. We study such events for an overdamped
colloidal system by the means of Brownian dynamics simulations. While it is
difficult to relate cage breaking events to structural mean field results in
bulk, we show that the microscopic dynamics of particles close to a wall can be
related to the anisotropic two-particle density. In particular, we study
cage-breaking trajectories, mean forces on a tracked particle, and the impact
of the history of trajectories. Based on our simulation results, we further
construct two different one-particle random-walk models - one without and one
with memory incorporated - and find the local anisotropy and the
history-dependence of particles as crucial ingredients to describe the escape
from a cage. Finally, our detailed study of a rearrangement event close to a
wall not only reveals the memory effect of cages, but leads to a deeper insight
into the fundamental mechanisms of glassy dynamics.
