Complex Effective Action and Schwinger Effect

TL;DR

This review discusses the vacuum structure and pair production mechanisms in quantum field theory, highlighting the Schwinger effect, Hawking radiation, and potential experimental tests in novel materials like graphene.

Contribution

It provides a comprehensive review of the in-out formalism for vacuum and pair production, connecting theoretical concepts with current experimental and material science developments.

Findings

Vacuum pair production explained via complex action in in-out formalism

Magnetic fields in magnetars exceed Schwinger limit, enabling natural pair production

Graphene and Dirac/Weyl semimetals offer experimental platforms for QED phenomena

Abstract

Spontaneous pair production from background fields or spacetimes is one of the most prominent phenomena predicted by quantum field theory. The Schwinger mechanism of production of charged pairs by a strong electric field and the Hawking radiation of all species of particles from a black hole are the consequence of nonperturbative quantum effects. In this review article, the vacuum structure and pair production is reviewed in the in-out formalism, which provides a consistent framework for quantum field theory in the sense that the complex action explains not only the vacuum persistence but also pair production. The current technology of intense lasers is still lower by a few order than the Schwinger limit for electron-positron pair production, while magnetic fields of magnetars on the surface are higher than the Schwinger limit and even higher at the core. On the other hand, the zero effective mass of electron and hole in graphene and Dirac or Weyl semimetals will open a window for experimental test of quantum electrodynamics (QED) phenomena in strong fields.