Bound-free electron-positron pair production in combined Coulomb and constant crossed electromagnetic fields: a Schwinger-like process with intrinsic assistance

The bound-free channel of electron-positron pair production by a highly charged bare ion in the presence of a strong constant crossed electromagnetic field is studied. To calculate the pair production rate, two different methods are applied and compared with each other: (i) a quasiclassical tunneling theory and (ii) a strong-field approximation, both equipped with appropriate Coulomb correction factors. The resulting rate, which depends nonperturbatively on both the Coulomb field of the ion and the constant crossed field, is calculated in a broad range of applied field strengths and nuclear charge numbers. Its functional form resembles the rate for a dynamically assisted Schwinger-like process, with the assistance being provided by the atomic binding energy of the created electron.

💡 Research Summary

This paper investigates the “bound-free” channel of electron-positron pair production, a fundamental process in Quantum Electrodynamics (QED), occurring in the presence of a highly charged bare ion and a strong, constant crossed electromagnetic field. The study focuses on how the interplay between the static Coulomb field of a heavy nucleus and an external intense electromagnetic field modifies the vacuum decay rate.

To achieve high precision, the researchers employed two distinct theoretical frameworks: (i) a quasiclassical tunneling theory and (ii) a strong-field approximation (SFA). A critical component of their methodology was the integration of appropriate Coulomb correction factors into both approaches. These corrections are essential to account for the non-perturbative influence of the ion’s electric field, which significantly alters the tunneling dynamics compared to pure vacuum Schwinger production.

The core finding of the research is the identification of an “intrinsic assistance” mechanism. While the traditional “dynamically assisted” Schwinger process relies on an external high-frequency field to lower the production barrier, this study demonstrates that the atomic binding energy of the electron—which remains captured by the ion in the bound-free channel—acts as an internal catalyst. This binding energy effectively reduces the energy threshold required for pair production, thereby enhancing the production rate.

The calculated production rate exhibits a complex, non-perturbative dependence on both the nuclear charge number ($Z$) and the strength of the applied external field. The results are valid across a wide range of field strengths and nuclear charges, providing a robust theoretical map for extreme electromagnetic environments. This research offers profound insights into the physics of particle production in extreme conditions, such as those found in ultra-intense laser-matter interactions or high-energy heavy-ion collisions, where the presence of strong Coulombic and external electromagnetic fields is inevitable.