Path integral formulation of quantum electrodynamics from classical particle trajectories

The classical particle interactions based on a covariant action principle directly lead, after path integration to the perturbation expansion of QED and to Feynman graphs without the intermediary of quantized fields Both scalar electrodynamics and spinor electrodynamics are treated The latter is based on a covariant classical model of the Dirac electron which already provides the notion of antiparticles and zitterbewegung so that vacuum polarization and pair production can also be discussed We give a procedure on how classical spin leads to quantum spin in successive time-sliced integrations