1,720,992 research outputs found
Quantum radiation reaction : Analytical approximations and obtaining the spectrum from moments
No full textWe derive analytical χ≪1 approximations for spin-dependent quantum radiation reaction for locally constant and locally monochromatic fields. We show how to factor out fast spin oscillations and obtain the degree of polarization in the plane orthogonal to the magnetic field from the Frobenius norm of the Mueller matrix. We show that spin effects lead to a transseries in χ, with powers χk, logarithms (ln χ)k, and oscillating terms, coso(.../χ) and sin (.../χ). In our approach we can obtain each moment, <(kP)m>, of the light-front longitudinal momentum independently of the other moments and without considering the spectrum. We show how to obtain a low-energy expansion of the spectrum from the moments by treating m as a continuous, complex parameter and performing an inverse Mellin transform. We also show how to obtain the spectrum, without making a low-energy approximation, from a handful of moments using the principle of maximum entropy
Quantum and Classical Radiation Reaction from Lightfront QED
No full textWe examine dynamical radiation reaction in lightfront QED. We take the classical limit and compare with predictions from various classical equations of motion
Ellipticity Induced in Vacuum Birefringence
No full textWe 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
Quantum radiation reaction spectrum of electrons in plane waves
No full textIn previous works we derived equations for the average momentum of high-energy electrons experiencing quantum radiation reaction in strong electromagnetic plane-wave background fields. In this paper we derive similar equations for the momentum spectrum. We formulate the equations in terms of the cumulative function and study the relation between the equations for the spectrum and the equations for the moments, analyze the structure of the low-energy expansions, and finally explain how our formulation is essentially in terms of a "Green's function"which allows us to study the dynamics without choosing a specific initial wave packet (or particle-bunch distribution)
Resummation of the α expansion for nonlinear pair production by an electron in a strong electromagnetic field
No full textWe show how to resum the Furry-picture α expansion in order to take quantum radiation reaction and spin transition into account in the nonlinear trident process in (pulsed) plane-wave background fields. The results are therefore nontrivial functions of both the background field strength, eE, and the coupling to the quantized photon field, α=e2/4π. The effective expansion parameter, T, is α times eE/mω≫1, which makes higher orders in α important. We show that they can change the sign of the spin-dependent part already at T<1, which will be experimentally accessible. We also present a new resummation method that essentially does to a convergent series what Borel-Padé resummation does to an asymptotic series
Quantum and classical radiation reaction from lightfront QED
No full textIn 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
Nonlinear trident in the high-energy limit: Nonlocality, Coulomb field, and resummations
No full textPair production, vacuum birefringence and radiation reaction in strong field QED
No full textIn 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
Nonlinear photon trident versus double Compton scattering and resummation of one-step terms
No full textThermally versus dynamically assisted Schwinger pair production
No full textWe study electron-positron pair production by the combination of a strong, constant electric field and a thermal background. We show that this process is similar to dynamically assisted Schwinger pair production, where the strong field is instead assisted by another coherent field, which is weaker but faster. We treat the interaction with the photons from the thermal background perturbatively, while the interaction with the electric field is nonperturbative (i.e., a Furry picture expansion in α). At O(α2) we have ordinary perturbative Breit-Wheeler pair production assisted nonperturbatively by the electric field. Already at this order we recover the same exponential part of the probability as previous studies, which did not expand in α. This means that we do not have to consider higher orders, so our approach allows us to calculate the preexponential part of the probability, which has not been obtained before in this regime. Although the prefactor is in general subdominant compared to the exponential part, in this case it can be important because it scales as α2≪1 and is therefore much smaller than the prefactor at O(α0) (pure Schwinger pair production). We show that, because of the exponential enhancement, O(α2) still gives the dominant contribution for temperatures above a certain threshold, but, because of the small prefactor, the threshold is higher than what the exponential alone would suggest
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