In this article, we review recent theoretical works on the Schwingermechanism
of particle production in external electrical fields. Although the
non-perturbative Schwinger mechanism is at the center of this discussion, many
of the approaches that we discuss can cope with general time and space
dependent fields, and therefore also capture the perturbative contributions to
particle production.Comment: Review for Progress in Particle and Nuclear Physics. 76 pages, 36
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