 They implicitly involve initial and final states of the non-interaction Hamiltonian formula_2, gradually transformed into states of the full Hamiltonian in accordance with the adiabatic theorem by "turning on" the interaction Hamiltonian (the gauge coupling).The expansion of the Dyson series in terms of Feynman diagrams will include vertices that couple "physical" particles (those that can appear in asymptotic states of the free Hamiltonian) to "unphysical" particles (states of fields that live outside the kernel of "sB" or inside the image of "sB") and vertices that couple "unphysical" particles to one another.T.