The recoils of a dynamical mirror and the decoherence of its fluxes

In order to address the problem of the validity of the ''background field approximation'', we introduce a dynamical model for a mirror described by a massive quantum field. We analyze the properties of the scattering of a massless field from this dynamical mirror and compare the results with the corresponding quantities evaluated using the original Davies Fulling model in which the mirror is represented by a boundary condition imposed on the massless field at its surface. We show that the recoils of the dynamical mirror induce decoherence effects which subsist even when the mass of the mirror is sent to infinity. In particular we study the case of the uniformly accelerated mirror and prove that, after a certain lapse of proper time, the decoherence effects inevitably dominate the physics of the quanta emitted forward. Then, the vanishing of the mean flux obtained in the Davies Fulling model is no longer found but replaced by a positive incoherent flux.