The fate of infrared divergences in a finite formulation of field theory: QED revisited

Within the framework of the recently proposed Taylor-Lagrange regularization procedure, we reanalyze the calculation of radiative corrections in quantum electrodynamics (QED) at next to leading order. Starting from a well-defined local bare Lagrangian, the use of this regularization procedure enables us to manipulate fully finite elementary amplitudes in the ultra-violet (UV) as well as infrared (IR) regimes, in physical D=4 space-time dimensions and for physical massless photons, as required by gauge invariance. We can thus separately calculate the electromagnetic form factors of the electron and the cross-section for real photon emission, each quantity being finite in these physical conditions. We then discuss the renormalization group (RG) equations within this regularization procedure. Thanks to the taming of IR divergencies, the RG equation associated to the (physical) effective charge exhibits an UV stable fixed point at alpha*=0, showing an asymptotic freedom-type behavior. We finally consider the case of two mass scales, one low and one heavy, paying particular attention to the natural decoupling properties between heavy and light degrees of freedom. As a direct consequence, the fine structure constant should be zero in the limit of massless electrons.