| 1. |
- Dinu, V., et al.
(författare)
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Photon polarization in light-by-light scattering: Finite size effects
- 2014
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010 .- 2470-0029. ; 90:4
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Tidskriftsartikel (refereegranskat)abstract
- We derive a simple expression for the photon helicity and polarization-flip probabilities in arbitrary background fields, in the low-energy regime. Taking the background to model a focused laser beam, we study the impact of pulse shape and collision geometry on the probabilities and on ellipticity signals of vacuum birefringence. We find that models which do not account for pulse duration can overestimate all signals in near head-on collisions by up to an order of magnitude. Taking pulse duration into account, the flip probability becomes relatively insensitive to both angular incidence and the fine details of the pulse structure.
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| 2. |
- Dinu, Victor, et al.
(författare)
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Quantum Radiation Reaction: From Interference to Incoherence
- 2016
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 116:4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate quantum radiation reaction in laser-electron interactions across different energy and intensity regimes. Using a fully quantum approach which also accounts exactly for the effect of the strong laser pulse on the electron motion, we identify in particular a regime in which radiation reaction is dominated by quantum interference. We find signatures of quantum radiation reaction in the electron spectra which have no classical analogue and which cannot be captured by the incoherent approximations typically used in the high-intensity regime. These signatures are measurable with presently available laser and accelerator technology.
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| 3. |
- Dinu, V., et al.
(författare)
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Vacuum refractive indices and helicity flip in strong-field QED
- 2014
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010 .- 2470-0029. ; 89:12
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Tidskriftsartikel (refereegranskat)abstract
- Vacuum birefringence is governed by the amplitude for a photon to flip helicity or polarization state in an external field. Here, we calculate the flip and nonflip amplitudes in arbitrary plane wave backgrounds, along with the induced spacetime-dependent refractive indices of the vacuum. We compare the behavior of the amplitudes in the low energy and high energy regimes, and analyze the impact of pulse shape and energy. We also provide the first lightfront-QED derivation of the coefficients in the Heisenberg-Euler effective action.
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| 4. |
- Gies, H., et al.
(författare)
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Critical Schwinger Pair Production
- 2016
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 116:9
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Tidskriftsartikel (refereegranskat)abstract
- We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential Berezinskii-Kosterlitz-Thouless-type scaling, and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality.
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| 5. |
- Ilderton, Antony, 1978, et al.
(författare)
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Nonperturbative pair production in interpolating fields
- 2015
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010 .- 2470-0029. ; 92:6, s. artikel nr 065001-
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Tidskriftsartikel (refereegranskat)abstract
- We compare the effects of timelike, lightlike and spacelike one-dimensional inhomogeneities on the probability of nonperturbative pair production in strong fields. Using interpolating coordinates we give a unifying picture in which the effect of the inhomogeneity is encoded in branch cuts and poles circulated by complex worldline instantons. For spacelike inhomogeneities the length of the cut is related to the existence of critical points, while for lightlike inhomogeneities the cut contracts to a pole and the instantons become contractible to points, leading to simplifications particular to the lightlike case. We calculate the effective action in fields with up to three nonzero components, and investigate its behavior under changes in field dependence.
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| 6. |
- Ilderton, Antony, 1978, et al.
(författare)
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Pair production from residues of complex worldline instantons
- 2015
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010 .- 2470-0029. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- We study nonperturbative pair production in electric fields with lightlike inhomogeneities, using complex worldline instantons. We show that the instanton contribution to the pair production probability is a complex contour integral over the instanton itself, and that pair production in the considered fields can be recast in terms of Cauchy's residue theorem. The instantons contribute residues from the poles they circulate (i.e. give local contributions), and the invariance of complex integrals under contour deformation manifests in the instanton contributions as invariance under a set of generalized, complex, reparametrizations.
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| 7. |
- Ilderton, Antony, 1978, et al.
(författare)
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Radiation reaction from QED: Lightfront perturbation theory in a plane wave background
- 2013
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 2470-0010 .- 2470-0029. ; 88:2
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Tidskriftsartikel (refereegranskat)abstract
- We derive dynamical, real time radiation reaction effects from lightfront QED. Combining the Hamiltonian formalism with a plane wave background field, the calculation is performed in the Furry picture for which the background is treated exactly while interactions between quantum fields are treated in perturbation theory as normal. We work to a fixed order in perturbation theory, but no other approximation is made. The literature contains many proposals for the correct classical equation describing a radiating particle; we take the classical limit of our results and identify which equations are consistent with QED.
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| 8. |
- Ilderton, Antony, 1978, et al.
(författare)
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Radiation reaction in strong field QED
- 2013
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 725:4-5, s. 481-486
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Tidskriftsartikel (refereegranskat)abstract
- We derive radiation reaction from QED in a strong background field. We identify, in general, the diagrams and processes contributing to recoil effects in the average momentum of a scattered electron, using perturbation theory in the Furry picture: we work to lowest nontrivial order in a. For the explicit example of scattering in a plane wave background, we compare QED with classical electrodynamics in the limit h -> 0, finding agreement with the Lorentz-Abraham-Dirac and Landau-Lifshitz equations, and with Larmor's formula. The first quantum corrections are also presented.
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| 9. |
- Ilderton, Antony, 1978, et al.
(författare)
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Worldline approach to helicity flip in plane waves
- 2016
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 93:8
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Tidskriftsartikel (refereegranskat)abstract
- We apply worldline methods to the study of vacuum polarization effects in plane wave backgrounds, in both scalar and spinor QED. We calculate helicity-flip probabilities to one loop order and treated exactly in the background field, and provide a toolkit of methods for use in investigations of higher-order processes. We also discuss the connections between the worldline, S-matrix, and lightfront approaches to vacuum polarization effects.
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| 10. |
- Torgrimsson, Greger, 1989
(författare)
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Ellipticity Induced in Vacuum Birefringence
- 2015
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 56:6-9, s. 615-620
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Tidskriftsartikel (refereegranskat)abstract
- We consider signals of photon-photon scattering in laser-based, low energy experiments. In particular, we consider the ellipticity induced on a probe beam by a strong background field, and compare it with a recent worldline expression for the photon polarisation flip amplitude. When the probe and the background are plane waves, the ellipticity is equal to the flip amplitude. Here we investigate the ellipticity-amplitude relation for more physical fields.
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| 11. |
- Torgrimsson, Greger, 1989
(författare)
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Pair production, vacuum birefringence and radiation reaction in strong field QED
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we consider three QED phenomena in strong electromagnetic fields: Schwinger pair production, vacuum birefringence and radiation reaction. We study electron-positron pair production in a variety of field configurations and, using complex worldline instantons, reveal new insights into the case of fields with lightlike inhomogeneities. We also find universal scaling for the pair production probability near critical points.Vacuum birefringence is the change in polarisation of a probe laser beam induced by interaction with a second electromagnetic field. We relate this macroscopic phenomena to the microscopic physics of individual photons in the probe flipping polarisation or helicity in a strong background field, and use this to make predictions for upcoming birefringence experiments, by considering the impact of realistic field geometry.Radiation reaction is the recoil effect on the motion of a radiating particle as it is accelerated by a background field. Due to the existence of unphysical solutions to the equation of motion derived in classical electrodynamics, several alternative classical equations have been proposed. We derive radiation reaction from QED and take the classical limit to test the validity of a number of these classical equations. Choosing a plane wave background allows us to treat the background field exactly and also to make general predictions about the form of a classical equation. We treat both vacuum birefringence and radiation reaction in a field theory formalism that naturally lends itself to systems with plane wave backgrounds - namely lightfront quantisation.
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| 12. |
- Torgrimsson, Greger, 1989
(författare)
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Quantum and Classical Radiation Reaction from Lightfront QED
- 2014
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Ingår i: Few-Body Systems. - : Springer Science and Business Media LLC. - 1432-5411 .- 0177-7963. ; 55:5-7, s. 501-506
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Tidskriftsartikel (refereegranskat)abstract
- We examine dynamical radiation reaction in lightfront QED. We take the classical limit and compare with predictions from various classical equations of motion.
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| 13. |
- Torgrimsson, Greger, 1989
(författare)
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Quantum and classical radiation reaction from lightfront QED
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I will study the motion of a radiating electron in a background field. Due to the existence of unphysical solutions to the equation of motion derived in classical electrodynamics, several alternative classical equations have been proposed. To test the validity of these equations, we compare their predictions with the classical limit of QED, using lightfront quantisation.
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