We present a canonical formalism facilitating investigations of the dynamical
Casimir effect by means of a response theory approach. We consider a massless
scalar field confined inside of an arbitaray domain G(t), which undergoes
small displacements for a certain period of time. Under rather general
conditions a formula for the number of created particles per mode is derived.
The pertubative approach reveals the occurance of two generic processes
contributing to the particle production: the squeezing of the vacuum by
changing the shape and an acceleration effect due to motion af the boundaries.
The method is applied to the configuration of moving mirror(s). Some properties
as well as the relation to local Green function methods are discussed.
PACS-numbers: 12.20; 42.50; 03.70.+k; 42.65.Vh Keywords: Dynamical Casimir
effect; Moving mirrors; Cavity quantum field theory; Vibrating boundary
