Schwinger pair creation of particles and strings

I shortly review the worldline instanton method for calculating Schwinger pair production rates in (i) one-loop QED (ii) multiloop QED and (iii) one-loop open string theory. 1. History Already in 1931 F. Sauter [1] realized that Dirac’s theory of the electron predicts that an electric field of sufficient strength and extent can induce spontaneous creation of electron – positron pairs from the vacuum. Naively, a virtual pair turns real by separating out along the field and drawing a sufficient amount of energy from it to make up for both rest mass energies (fig. 1). 2