Advances in QED with intense background fields

Abstract: Upcoming and planned experiments combining increasingly intense lasers and energetic particle beams will access new regimes of nonlinear, relativistic, quantum effects. This improved experimental capability has driven substantial progress in QED in intense background fields. We review here the advances made during the last decade, with a focus on theory and phenomenology. As ever higher intensities are reached, it becomes necessary to consider processes at higher orders in both the number of scattered particles and the number of loops, and to account for non-perturbative physics (e.g. the Schwinger effect), with extreme intensities requiring resummation of the loop expansion. In addition to increased intensity, experiments will reach higher accuracy, and these improvements are being matched by developments in theory such as in approximation frameworks, the description of finite-size effects, and the range of physical phenomena analysed. Topics on which there has been substantial progress include: radiation reaction, spin and polarisation, nonlinear quantum vacuum effects and connections to other fields including physics beyond the Standard Model.

• The paper presents major advances in QED with intense laser fields, demonstrating experiments that push the coupling parameter ξ to ~100.
• Refined approximation methods, such as the locally constant field approximation, enable precise modeling of nonlinear, non-perturbative quantum effects.
• The study details non-perturbative phenomena like the Schwinger effect and light–by–light scattering, opening new avenues for probing physics beyond the Standard Model.

Advances in QED with Intense Background Fields

The paper at hand offers a comprehensive review of recent advancements in Quantum Electrodynamics (QED) when electrons interact with intense background fields such as those generated by high-intensity lasers. The field of intense laser-matter interactions has significantly progressed over the past decade, driven by developments in both experimental capabilities and theoretical understanding. This progress opens the door to probing new regimes of nonlinear, relativistic, quantum effects, crucial for understanding light-matter interactions at high intensities.

High-Intensity Experimental Landscape

The recent advancements in QED with intense background fields are largely propelled by the coming of age of high-intensity laser facilities. Facilities are equipped to generate electromagnetic fields that can push the interaction strength or coupling (characterized through the dimensionless parameter, $\xi$) to levels where this coupling can significantly modify the particle dynamics. Experiments now routinely reach or will soon reach values of $\xi \sim 10^2$ and beyond, marking the entry into the so-called "intensity frontier" of the Standard Model. These intense background fields facilitate investigations into non-perturbative quantum field phenomena, like vacuum pair production and vacuum birefringence.

Theoretical and Phenomenological Advances

The paper outlines several key theoretical advancements in understanding QED in intense fields:

1. Nonlinear QED Phenomena: As field intensities rise, higher orders of QED processes need attention, accounting for multiple scattered particles and loop corrections.
2. Approximation Techniques: For theoretical predictions to align with new experimental regimes, approximation frameworks (e.g., the locally constant field approximation) have been refined, allowing accurate modeling of first- and second-order processes even in intense, highly varying fields. These play a pivotal role in computational simulations supporting experimental setups.
3. Non-Perturbative Effects: The Schwinger effect stands as a hallmark non-perturbative process, demonstrating spontaneous particle creation in strong fields. New insights are being sought into its dynamics beyond constant fields, considering timed and space-dependent configurations.
4. Light-By-Light Scattering: There is significant interest in observing vacuum polarization effects, prominent in light-by-light scattering, leading to potential tests of QED beyond traditional particle accelerators.

Future Directions and Implications

The frontier of high-intensity interactions in QED hints at broader implications and future avenues:

• New Particle Search: The dramatic field strengths might enable searches for physics beyond the Standard Model, including axion-like particles or dark photons, which traditionally excel in coupling tests in intense fields.
• Seminal Connections to Astrophysics: Findings at the interplay of high-intensity field labs and QED serve as analogs to extreme astrophysical environments like magnetospheres of exotic stars, offering terrestrial insight into space phenomena.

In conclusion, the successful interaction of experiment and theory in handling QED with intense background fields marks a robust leap in exploring and verifying fundamental physics aspects. The developments charted in this paper underscore the ongoing transition of previously theoretical principles into physically accessible, testable quantum phenomena—an evolution that promises to further blur the lines between laboratory physics and cosmic scales in the study of electromagnetism.