Non-Additivity of Nonequilibrium Atom-Surface Forces

The motion-induced drag force acting on a particle moving within a planar cavity - a relevant configuration for many experimental investigations - is calculated. This drag force exhibits a markedly non-additive nature and can evaluate to about an order of magnitude larger than the corresponding additive approximation. Particular focus is placed on the nonequilibrium statistics of the interaction and on the interplay of the system's geometry with the different dissipative processes that simultaneously occur in the system.