Singular structure of the QED effective action
The equations for the QED effective action derived in \cite{fm} are considered using singular perturbation theory. The effective action is divided into regular and singular (in coupling constant) parts. It is shown that expression for the regular part coincides with usual Feynman perturbation series over coupling constant, while the remainder has essential singularity at the vanishing coupling constant: $e\rightarrow 0$. This means that in the frame of quantum field theory it is impossible "to switch off" electromagnetic interaction in general and pass on to "free electron".
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