Perturbative description of the fermionic projector: normalization, causality and Furry’s theorem

The causal perturbation expansion of the fermionic projector is per- formed with a contour integral method. Different normalization conditions are analyzed. It is shown that the corresponding light-cone expansions are causal in the sense that they only involve bounded line integrals. For the resulting loop diagrams we prove a generalized Furry theorem