Schwinger mechanism revisited (1510.05451v2)

Abstract: 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.

Overview of "Schwinger mechanism revisited"

The paper "Schwinger mechanism revisited" by François Gelis and Naoto Tanji provides an in-depth review of theoretical advancements related to the Schwinger mechanism, a non-perturbative process by which electron-positron pairs are produced in the presence of strong electric fields. This mechanism originates from the concept of quantum tunneling across the Dirac sea, where virtual charged particles can become real through the energy provided by an external field. The paper revisits various aspects of this phenomenon, emphasizing new theoretical frameworks and numerical approaches that extend the understanding and applicability of this fundamental mechanism.

Schwinger Mechanism and External Fields

The Schwinger mechanism describes pair production as a non-perturbative quantum field theory (QFT) effect, occurring when an electric field is sufficiently strong to create observable particles from the vacuum. The authors discuss the dependence of the process on the intensity of the external field, with notable focus on time-independent fields, which present inherent non-perturbative challenges. The transition rates are characterized by an exponential dependence on the inverse of the electric field strength, implying the necessity of high field strength for significant particle production.

Theoretical Formulations and Approaches

The paper outlines both traditional QFT methods and modern theoretical developments:

1. Mode Function Approach: This involves solving wave equations for fields in the presence of external sources, providing insights into spectra and distribution functions of created particles.
2. Worldline Formalism: Originating from string-inspired techniques, the worldline approach offers elegant ways of computing effective actions and rates of pair production. It emphasizes the spacetime paths of particles, integrating over all possible trajectories to capture the dynamics of pair creation.
3. Cutting Rules and Keldysh Formalism: These provide a method for handling imaginary components of transition amplitudes, which are crucial for understanding particle production in strong fields.
4. Quantum Kinetic and Wigner Formulations: These theories look at the kinetic properties and phase-space distributions of particles, crucial for understanding dynamic evolution in varying fields.

Numerical Techniques and Lattice Simulations

The paper describes advancements in computational approaches, particularly using lattice simulations to handle the complexities of space-time-dependent fields where analytical solutions aren’t feasible. The authors emphasize the challenges posed by fermion doublers in lattice theories, and highlight statistical sampling methods that reduce computational costs while maintaining accuracy.

Implications and Applications

1. QCD and Glasma Flux Tubes: The authors discuss extensions of the Schwinger mechanism to Quantum Chromodynamics (QCD), where strong color fields in heavy-ion collisions can similarly produce quark-antiquark pairs, a phenomenon of substantial interest in high-energy physics.
2. Dynamically Assisted Schwinger Effect: Combining strong and fast-varying weaker fields can enhance pair production rates significantly - an area of exploration for experimental realization, especially with modern laser systems.
3. Cosmological and Condensed Matter Physics: While not extensively covered, the paper hints at the relevance of Schwinger processes in early universe conditions and materials like graphene, indicating the compelling interdisciplinary applications.

Conclusion and Future Directions

The review emphasizes that while key theoretical frameworks and computational techniques have matured, ongoing research is directed towards exploring Schwinger processes in more complex, realistic environments, such as those encountered in high-energy experiments and astrophysical phenomena. The interplay between computational advancements and theoretical innovations continues to be a fertile ground for future discoveries, potentially facilitating observations of the Schwinger effect in upcoming experimental endeavors.