Historical research guide · 0943 · 2023

Advances in QED with intense background fields

A. Fedotov · A. Ilderton · F. Karbstein · B. King · D. Seipt · H. Taya · G. Torgrimsson

In one minute

Seven theorists take stock of a decade of quantum electrodynamics in strong background fields — the physics of what happens when light becomes intense enough to change the vacuum itself. Modern lasers now routinely pack more than one photon into a cube of the electron’s Compton wavelength. At that point the coupling between a charge and the field grows large enough that the usual perturbation series breaks down, even though the fine-structure constant stays as small as ever: non-perturbative physics at weak coupling. The review sets out the three dimensionless numbers that govern the regime, surveys what is now understood — nonlinear Compton scattering, Breit-Wheeler pair creation, radiation reaction, light-by-light scattering, vacuum birefringence, the Schwinger effect — and states plainly what is still open, including whether the loop expansion itself must be resummed at extreme intensity. Its closing note is a wager on the near future: the machines that will test all of this, at SLAC, at DESY and at the new multi-petawatt laser facilities, are being commissioned now.

Connection

Chapter 2 argues that the vacuum is a real medium with properties you can measure and change; this review is the current state of the art on exactly that — what field strength makes empty space birefringent, what makes it produce matter, and which experiments are being built to see it. Chapter 4 picks up the thread the authors leave at the end, where the same strong-background methods are being carried across into gravity, graviton amplitudes and background gravitational fields.

From the source

In an intense laser pulse the charge-field coupling becomes large while the fine-structure constant stays small — the photon density scales as the squared intensity parameter divided by the fine-structure constant, and the effective coupling is the intensity parameter itself, which now easily exceeds one. The interaction with the laser must therefore be treated to all orders, or non-perturbatively; this is non-perturbativity at weak coupling.Section 1, Introduction, second paragraph
The quantum nonlinearity parameter measures the background electric field, in the rest frame of the accelerated charge, against the Schwinger limit — equivalently the work the background does over a Compton wavelength in that frame, in units of the rest energy, or the particle’s proper acceleration. When it reaches order one, quantum nonlinear processes such as pair creation become probable; in a plane wave it is the product of the classical intensity parameter and the linear quantum parameter.Section 1.1, Equation 1 and the surrounding definitions
The perturbative loop expansion of the Heisenberg-Euler effective Lagrangian breaks down for exponentially large fields, because the two-loop contribution is logarithmically enhanced in the strong-field limit and can surpass the one-loop one. That enhancement comes from one-particle-reducible diagrams which had previously been assumed, erroneously, to vanish.Section 7.1 and the light-by-light passage of Section 12; Equations 139 and 140
Strong-field QED has already been measured. The NA63 experiment at CERN, colliding hundred-gigaelectronvolt beams with oriented crystals, has measured the quantum suppression of synchrotron radiation over a range of quantum nonlinearity from 0.05 to 0.7, the Landau-Pomeranchuk-Migdal effect, and radiation reaction in the classical limit, verifying the Landau-Lifshitz equation.Section 1.1, Experimental landscape
A laser of 800 nanometre wavelength focused with linear polarisation to ten to the twenty-third watts per square centimetre reaches an intensity parameter of about 150, which will let the quantum nonlinear regime be probed with lasers for the first time; E320 at SLAC and LUXE at DESY will collide conventionally accelerated electron beams with intense pulses, while CoReLS is online, ELI is being commissioned and SEL is under construction.Section 1, closing paragraphs; Section 1.1
The authors point the methods outward: efficient techniques now exist for extracting the classical limit of observables from quantum scattering amplitudes without computing the full amplitude, worldline and double-copy methods have been applied to graviton scattering, and there remains a great deal of work to be done extending them to include background gravitational fields.Sections 11.4 and 11.5; the Beyond QED passage of Section 12

The way in

https://doi.org/10.1016/j.physrep.2023.01.003

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

LICENCE VERIFIED AT ARTICLE LEVEL, FROM THE PUBLISHER’S OWN DEPOSIT. Elsevier’s Crossref record for this DOI carries an article-level licence for the version of record pointing to http://creativecommons.org/licenses/by/4.0/, and INSPIRE-HEP records the same, listing ‘CC BY 4.0’ for the publication and, separately, ‘arXiv nonexclusive-distrib 1.0’ for the preprint. FETCH. ScienceDirect answered every automated request with 403, so the typeset version of record could not be read here; the text below was read from the accepted manuscript, arXiv 2203.00019 version 2 of 31 January 2023, whose title page reads ‘Preprint submitted to Elsevier’ and whose journal reference is Physics Reports 1010, pages 1 to 138. Readers who need the typeset article should go to the DOI. WHICH SECTIONS ARE REPRODUCED. This is a 138-page review and it is not reproduced whole. Reproduced here: the Abstract in full; the opening of Section 1, Introduction; the parameter definitions from Section 1.1, Experimental landscape; and from Section 12, Conclusions and open questions, the opening, the passages on light-by-light scattering, the Schwinger effect, the Ritus-Narozhny conjecture and Beyond QED, and the closing summary. Sections 2 to 11 — the technical body on first- and second-order processes, approximation frameworks, higher-order processes and resummation, light-by-light scattering, the Schwinger effect, the Ritus-Narozhny conjecture, backgrounds beyond plane waves, and connections beyond QED — are omitted for length; the complete text is at the source. CLEANING. Running heads, page numbers, figure panels and reference-number markers have been dropped; display equations are rendered in words keyed to their source equation numbers; inequalities and Greek symbols are written out.

How to cite it

A. Fedotov, A. Ilderton, F. Karbstein, B. King, D. Seipt, H. Taya, G. Torgrimsson (2023) Advances in QED with intense background fields doi:10.1016/j.physrep.2023.01.003

In one minute

From the source

The way in

How to cite it

Where it sits in the curriculum