Extended locally constant field approximation for nonlinear Compton scattering

Ilderton, Anton; King, B.; Seipt, D.

doi:10.1103/physreva.99.042121

Cited by 142 publications

(136 citation statements)

References 54 publications

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“…(13) even for the case of delta-function pulses with little internal structure. However, such examples would provide us with improved insight into physics in strong fields, allow us to better check numerical methods and approximations [39][40][41], and could also provide particular data to help analyse the double copy [45][46][47][48][49] of gauge theory on background plane waves [34,50,51]. It would also be very interesting to see how much progress can be made with challenging higher-order (many vertex) processes in delta-pulse backgrounds.…”

Section: Discussionmentioning

confidence: 99%

“…Processes in constant crossed fields (the zero frequency limit of plane waves) can scale with powers of a 2/3 0 [12][13][14][15][16], which has lead to a conjecture that for sufficiently high a 0 the Furry expansion as used here breaks down. If one invokes the "locally constant field approximation" (LCFA) [4] then the power-law scaling generalises to more general fields [37,38], but due to the many shortcomings of the LCFA [37][38][39][40][41][42] it would be desirable to have exact analytic results. As we have a closed form result, (13), we may simply expand it for large a 0 , finding…”

Section: A Total Probabilitymentioning

confidence: 99%

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Exact results for scattering on ultrashort plane wave backgrounds

Ilderton

2019

Phys. Rev. D

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We give exact results for the emission spectra of both nonlinear Breit-Wheeler pair production and nonlinear Compton scattering in ultra-intense, ultra-short duration plane wave backgrounds, modelled as delta-function pulses. This includes closed form expressions for total scattering probabilities. We show explicitly that these probabilities do not exhibit the power-law scaling with intensity associated with the conjectured breakdown of (Furry picture) perturbation theory, instead scaling logarithmically in the high-intensity limit. I. INTRODUCTIONThe coupling of matter to a background field can be arbitrarily strong, requiring non-perturbative methods in the calculation of scattering amplitudes on the background. Highly symmetric backgrounds such as electromagnetic plane waves [1][2][3], widely used as a first model of intense laser fields [4][5][6][7], may be treated exactly for arbitrarily high field strength, allowing a great deal of analytic progress to be made in the calculation of scattering amplitudes.However, the evaluation of observables still requires intense numerical integration. While various results have been found which allow more efficient calculation [8][9][10], it would be desirable to have exact results when confronting questions of a fundamental nature, such as the limits of perturbation theory in the high intensity regime; it has been conjectured that (Furry picture [11]) perturbation theory in strong fields breaks down for sufficiently high field strengths, due to a power-law scaling of higher loop processes [12][13][14][15][16]. If true, this would invalidate current perturbative or semi-perturabtive approaches to QED in strong backgrounds [17,18].Here we have two objectives. The first is to provide some exact results for scattering on ultra-short plane wave pulses. This includes closed-form expressions for total probabilities. Our second objective is to investigate the highintensity scaling of these results in light of the conjectured high-intensity breakdown. The model on which this conjecture is based, and the starting point for many investigations of laser-matter interactions, assumes the laser fields may be treated as constant and homogeneous [4]. We consider here the opposite limit in which the field is of infinitely short duration, being modelled as a sequence of delta function pulses. This will allow us to provide exact results: see also [19] for the use of delta pulses, in combination with constant fields, to Schwinger pair production, where exact results are also obtained.This paper is organised as follows. In Sect. I A we review some necessary structures of QED scattering in plane wave backgrounds. In Sect. II we consider stimulated pair production in a delta-function pulse. Both the differential emission spectra and the total pair creation probability are obtained in closed form, with all integrals performed. We show that the high-intensity scaling of the probability is logarithmic, not power law. We then consider the case of two delta function pulses modelling an oscillating f...

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Section: Discussionmentioning

confidence: 99%

Section: A Total Probabilitymentioning

confidence: 99%

Exact results for scattering on ultrashort plane wave backgrounds

Ilderton

2019

Phys. Rev. D

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“…A number of upcoming experiments aim to probe quantum processes in intense laser fields, including pair production [1], vacuum birefringence [2], and conjectured regimes where all current perturbative approaches to QED break down [3][4][5][6]. However, a series of theoretical investigations [7][8][9], as well as recent comparisons of theory with laser experiments [10,11], have highlighted shortcomings of existing models and simulations. A priority of the research field as a whole is hence the development of the right approximations and tools to more accurately model strong-field processes analytically and numerically.…”

Section: Introductionmentioning

confidence: 99%

Absorption cross section in an intense plane wave background

2019

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We consider the absorption of probe photons by electrons in the presence of an intense, pulsed, background field. Our analysis reveals an interplay between regularisation and gauge invariance which distinguishes absorption from its crossing-symmetric processes, as well as a physical interpretation of absorption in terms of degenerate processes in the weak field limit. In the strong field limit we develop a locally constant field approximation (LCFA) for absorption which also exhibits new features. We benchmark the LCFA against exact analytical calculations and explore its regime of validity. Pulse shape effects are also investigated, as well as infra-red and collinear limits of the absorption process.

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“…LCF+1 is obtained by including the next-to-leading order correction in an expansion in 1/a 0 , cf. [1,45]. The values a 0 = (1, 2, 4) and χ = a 0 b 0 = (0.5, 1, 2, 4, 8) are considered.…”

Section: Numerical Study Of the Trident Spectramentioning

confidence: 99%

“…Including the latter we obtained an approximation called LCF+1, cf. [1,45], which we plotted using dash-dotted lines. As seen from Fig.…”

Section: Numerical Study Of the Trident Spectramentioning

confidence: 99%

Trident process in laser pulses

Dinu

Torgrimsson

2020

Phys. Rev. D

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We study the trident process in laser pulses. We provide exact numerical results for all contributions, including the difficult exchange term. We show that all terms are in general important for a short pulse. For a long pulse we identify a term that gives the dominant contribution even if the intensity is only moderately high, a01, which is an experimentally important regime where the standard locally-constant-field (LCF) approximation cannot be used. We show that the spectrum has a richer structure at a0 ∼ 1, compared to the LCF regime a01. We study the convergence to LCF as a0 increases and how this convergence depends on the momentum of the initial electron. We also identify the terms that dominate at high energy.

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Extended locally constant field approximation for nonlinear Compton scattering

Cited by 142 publications

References 54 publications

Exact results for scattering on ultrashort plane wave backgrounds

Exact results for scattering on ultrashort plane wave backgrounds

Absorption cross section in an intense plane wave background

Trident process in laser pulses

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