Evolution modes of the vacuum Wigner function in strong-field QED
The physical content of a non-covariant quantum-field theoretic transport formalism for strong-field QED is addressed within an integral formulation of the evolution equations which highlights the relation to acoustic and Zitterbewegung modes of the field-free limit. Through the computation within this framework of the electric susceptibility of the vacuum at the one-loop level, it is established that the off-shell behaviour of the electron-positron field is correctly incorporated. The Zitterbewegung mode is seen to be solely responsible at the one-loop level for vacuum polarization. Implications for the full renormalisation of the theory are taken up.