TRANSLATIONAL SYMMETRY AND MICROSCOPIC PREPARATION IN OSCILLATOR MODELS OF QUANTUM DISSIPATION

It is shown that models of quantum dissipation based on interactions w hich are linear both in the bath and in the particle position coordina te cannot be strictly invariant under translations, even if counterter ms are included. This lack of symmetry manifests itself in an unphysic al dependence of the long time dynamics on the choice of initial condi tions for the particle-bath interaction. By properly expanding a Frohl ich type Hamiltonian, a simple model of homogeneous dissipation is dev eloped that is insensitive to the chosen microscopic preparation.