Perturbative Description of the Fermionic Projector: Normalization,   Causality and Furry's Theorem
  The causal perturbation expansion of the fermionic projector is performed 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. 
Felix Finster and J\"urgen Tolksdorf
math-ph hep-th math.MP