Schwinger pair production at nonzero temperatures or in compact directions

Electric fields may decay by quantum tunneling: as calculated by Schwinger, an electron-positron pair may be summoned from the vacuum. In this paper, I calculate the pair-production rate at nonzero temperatures. I find that, at high temperatures, the decay rate is dominated by a new instanton that involves both thermal fluctuation and quantum tunneling; this decay is exponentially faster than the rate in the literature. I also calculate the decay rate when the electric field wraps a compact circle (at zero temperature). The same new instanton also governs this rate: I find that, for small circles, decay is dominated by a process that drops the electric field by one unit, but does not produce charged particles.