Dressed and half-dressed neutral sources in nonrelativistic QED

A nonrelativistic, quantum-mechanical neutral source is considered, which is coupled to the quantized e.m. field in vacuo. The dressed ground state of the coupled system is obtained in terms of the bare ground state and of other excited states in absence of coupling. This dressed ground state is characterized by a cloud of virtual photons in the space surrounding the source, which yields nonvanishing quantum averages of the magnetic and electric field energy densities. The source-field coupling is modeled by a Craig-Power Hamiltonian, and the ground state energy densities are shown to behave like r-7 at distance r from the dressed source. Half-dressed sources are introduced as sources surrounded by incomplete virtual photon clouds. The time evolution of an initially bare source is discussed in terms of time-dependent field energy densities in the Heisenberg picture and it is shown to lead asymptotically to a fully dressed ground state source. The results obtained, as well as the limits of validity of the approach adopted, are discussed in the light of previous theories for charged half-dressed sources in quantum electro- and mesodynamics. (orig.)