Lorentzian worldline path integral approach to Schwinger effect

TL;DR

This paper introduces a Lorentzian worldline path integral method to analyze the Schwinger effect, providing a unified gauge approach and deriving particle production without special functions, with potential applications in complex electromagnetic fields.

Contribution

It develops a Lorentzian worldline path integral formalism for the Schwinger effect, enabling gauge-independent mode representation and direct calculation of particle production.

Findings

Unified treatment of Schwinger modes in different gauges

Exact Bogoliubov coefficients derived without special functions

Emergence of worldline instantons via saddle points

Abstract

We demonstrate that the positive frequency modes for a complex scalar field in a constant electric field (Schwinger modes), in three different gauges, can be represented as exact Lorentzian worldline path integral amplitudes. Although the mathematical forms of the mode functions differ in each gauge, we show that a simple prescription for Lorentzian worldlines' boundary conditions dispenses the Schwinger modes in all three gauges (that we considered) in a unified manner. Following that, using our formalism, we derive the exact Bogoliubov coefficients and, hence, the particle number, \textit{without} appealing to the well-known connection formulas for parabolic cylinder functions. This result is especially relevant in view of the fact that in a general electromagnetic field configuration, one does not have the luxury of closed-form solutions. We argue that the real time worldline path integral approach may be a promising alternative in such non-trivial cases. We also demonstrate, using Picard-Lefschetz theory, how the so-called worldline instantons emerge naturally from relevant saddle points that are complex.