Abstract:
The complex time method is used to show that length $l_C$ of formation of processes involving emission of photons and production of pairs in a constant external field can be determined correctly and that the resultant values of $l_C$ have not only qualitative, but also quantitative meaning. Analysis based on the complex time method makes it possible to express the amplitudes of processes in the form of rapidly converging integrals. It is found that the radiation formation length for low-energy (soft) photons decreases upon an increase in the radiation frequency in accordance with the familiar law $l_C\sim\omega^{-1/3}$, while for higher frequencies, this dependence changes to $l_C\sim\omega^{-1/2}$. The formulas derived for $l_C$ make it possible to indicate the accuracy with which this quantity can be treated as the radiation formation length.
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