The infrared problem and adiabatic switching

The infrared problem of QED is investigated by means of adiabatic switching of the interaction. The authors prove in lowest-order perturbation theory that the adiabatic limit of the inclusive cross section is independent of the switching function, provided four polarizations of soft bremsstrahlung are taken into account before the limit. This gives the possibility of simulating charged asymptotic states in a Fock space consisting only of free fields. Finally, they show that no (finite) charge renormalization is necessary in order to fix the physical charge. This turns out to be a consequence of the Ward identity.