arXiv subjects

B. King

Publications and source records attributed to B. King.

At least 55 records · Page 3Linked to original sources

arXiv2019

A uniform locally constant field approximation for photon-seeded pair production

A challenge to upcoming experiments that plan to collide a particle beam with laser pulses of moderate intensity is how to correctly incorporate quantum effects into simulation frameworks. Using a uniform approach, we extend the widely-used locally constant field approximation (LCFA) to derive an improved rate of photon-seeded pair creation (the nonlinear Breit-Wheeler process). By benchmarking our "ULCFA" expressions with the lightfront spectrum of: i) exact analytical results and ii) numerical integration of the QED probability for short pulses, we show that our extended approach remains accurate at smaller values of the intensity parameter than the standard LCFA.

hep-ph↗

arXiv2019

Axion-like-particle decay in strong electromagnetic backgrounds

The decay of a massive pseudoscalar, scalar and U(1) boson into an electron-positron pair in the presence of strong electromagnetic backgrounds is calculated. Of particular interest is the constant-crossed-field limit, relevant for experiments that aim to measure high-energy axion-like-particle conversion into electron-positron pairs in a magnetic field. The total probability depends on the quantum nonlinearity parameter - a product of field and lightfront momentum invariants. Depending on the seed particle mass, different decay regimes are identified. In the below-threshold case, we find the probability depends on a non-perturbative tunnelling exponent depending on the quantum parameter and the particle mass. In the above-threshold case, we find that when the quantum parameter is varied linearly, the probability oscillates nonlinearly around the spontaneous decay probability. A strong-field limit is identified in which the threshold is found to disappear. In modelling the fall-off of a quasi-constant-crossed magnetic field, we calculate probabilities beyond the constant limit and investigate when the decay probability can be regarded as locally constant.

hep-ph↗

arXiv2019

An extended locally constant field approximation for nonlinear Compton scattering

The locally constant field approximation (LCFA) has to date underpinned the numerical simulation of quantum processes in laser-plasma physics and astrophysics, but its validity has recently been questioned in the parameter regime of current laser experiments. While improvements are needed, literature corrections to the LCFA show inherent problems. Using nonlinear Compton scattering in laser fields to illustrate, we show here how to overcome the problems in LCFA corrections. We derive an "LCFA+" which, comparing with the full QED result, shows an improvement over the LCFA across the whole photon emission spectrum. We also demonstrate an implementation of our results in the type of numerical code used to design and analyse intense laser experiments.

hep-ph↗

arXiv2018

Light scalars: coherent nonlinear Thomson scattering and detection

Several theories of beyond-the-standard-model physics predict light scalars that couple to fermions. By extending classical electrodynamics to include an electron-scalar coupling, we calculate the nonlinear Thomson scattering of light scalars in the collision of an electron with a monochro- matic electromagnetic background. In doing so, we identify the classical electron-scalar current, which allows for straightforward inclusion of the process in laser-plasma particle-in-cell simulations. Scattering of pseudoscalar particles is found to vanish in the classical (or, equivalently, the low-lightfront-momentum) limit. When electrons co-propagate with the laser pulse, we demonstrate that coherence effects in the production of light scalar particles can greatly enhance the signal for sub-eV scalars. When the electron beams counter-propagate with the laser pulse, we demon- strate that experiments can probe larger scalar masses due to the larger momentum transfer in the collisions. We then discuss a possible lab-based experimental set-up to detect this scalar signal which is similar to light-shining-through-the-wall experiments. Using existing experimental facilities as benchmarks, we calculate projected exclusion bounds on the couplings of light scalars in such experiments.

hep-ph↗

arXiv2018

Three-pulse photon-photon scattering

We calculate signals of real photon-photon scattering in the collision of three laser pulses. Taking goal parameters from the Station of Extreme Light at the upcoming Shanghai Coherent Light Source, we consider two scenarios: i) the collision of three optical pulses; ii) the collision of an XFEL with two optical pulses. Although experimentally more difficult to perform, we find that colliding three laser pulses offers certain advantages in the detection of scattered photons by separating their frequency, momentum and polarisation from the background.

hep-ph↗

arXiv2018

Electron-seeded ALP production and ALP decay in an oscillating electromagnetic field

Certain models involving ALPs (axion-like-particles) allow for the coupling of scalars and pseudoscalars to fermions. A derivation of the total rate for production of massive scalars and pseudoscalars by an electron in a monochromatic, circularly-polarised electromagnetic background is presented. In addition, a derivation and the total rate for the decay of massive scalars and pseudoscalars into electron-positron pairs in the same electromagnetic background is given. We conclude by approximating the total yield of ALP production for a typical laser-particle experimental scenario.

hep-ph↗

arXiv2018

The effect of interference on the trident process in a constant crossed field

We perform a complete calculation of electron-seeded pair-creation (the trident process) in a constant crossed electromagnetic background. Unlike earlier treatments, we include the interference between exchange diagrams. We find this exchange interference can be written as a contribution solely to the one-step process, and for small quantum nonlinearity parameter is of the same order as other one-step terms. We find the exchange interference further suppresses the one-step process in this parameter regime. Our findings further support the crucial assumption made in laser-plasma simulation codes that at high intensities, the trident process can be well-approximated by repeated iteration of the single-vertex subprocesses. The applicability of this assumption to higher-vertex processes has fundamental importance to the development of simulation capabilities.

hep-ph↗

arXiv2017

Axion-like particle production in a laser-induced dynamical spacetime

We consider the dynamics of a charged particle (e.g., an electron) oscillating in a laser field in flat spacetime and describe it in terms of the variable mass metric. By applying Einstein's equivalence principle, we show that, after representing the electron motion in a time-dependent manner, the variable mass metric takes the form of the Friedmann-Lemaître-Robertson-Walker metric. We quantize a massive complex scalar or pseudo-scalar field in this spacetime and derive the production rate of electrically neutral, spinless particle-antiparticle pairs. We show that this approach can provide an alternative experimental method to axion searches.

hep-ph↗

arXiv2017

On beam models and their paraxial approximation

We derive focused laser pulse solutions to the electromagnetic wave equation in vacuum. After reproducing beam and pulse expressions for the well-known paraxial Gaussian and axicon cases, we apply the method to analyse a laser beam with Lorentzian transverse momentum distribution. Whilst a paraxial approach has some success close to the focal axis and within a Rayleigh range of the focal spot, we find that it incorrectly predicts the transverse fall-off typical of a Lorentzian. Our vector-potential approach is particularly relevant to calculation of quantum electrodynamical processes in weak laser pulse backgrounds.

physics.optics↗

arXiv2016

Beyond Volkov: Solving the Second-Order Klein-Gordon Equation

Whether monochromatic, pulsed, or even constant and crossed, the field used to describe the interaction of charged fermions with an intense laser beam is mainly assumed to be of plane-wave form. We consider a simple extension to plane-wave fields and consider a scalar particle in a non-lightlike, univariate and transverse propagating electromagnetic wave. The existence of some known exact solutions in this case allows us to analyse various proposed approximations in the literature as well as the plane wave model. The results also describe some of the quantum dynamics of a scalar particle in a standing wave background.

hep-ph↗

arXiv2016

Classical and quantum dynamics of a charged scalar particle in a background of two counterpropagating plane waves

We consider a scalar particle in a background formed by two counter-propagating plane waves. Two cases are studied: i) dynamics at a magnetic node and ii) zero initial transverse canonical momentum. The Lorentz and Klein-Gordon equations are solved for these cases and approximations analysed. For the magnetic node solution (homogeneous, time-dependent electric field), the modified Volkov wavefunction which arises from a high-energy approximation is found to be inaccurate for all energies and the solution itself unstable when photon emission (nonlinear Compton scattering) is included. For the zero initial transverse canonical momentum case, in both quantum and classical cases, forbidden parameter regimes, absent in the plane wave model, are identified.

quant-ph↗

arXiv2016

Vacuum birefringence in high-energy laser-electron collisions

Real photon-photon scattering is a long-predicted phenomenon that is being searched for in experiment in the form of a birefringent vacuum at optical and X-ray frequencies. We present results of calculations and numerical simulations for a scenario to measure this effect using multi-MeV photons generated in the collision of electrons with a laser pulse. We find that the birefringence of the vacuum should be measurable using experimental parameters attainable in the near future.

hep-ph↗

arXiv2015

Measuring Vacuum Polarisation with High Power Lasers

When exposed to intense electromagnetic fields, the quantum vacuum is expected to exhibit properties of a polarisable medium akin to a weakly nonlinear dielectric material. Various schemes have been proposed to measure such vacuum polarisation effects using a combination of high power lasers. Motivated by several planned experiments, we provide an overview of experimental signatures that have been suggested to confirm this prediction of quantum electrodynamics of real photon-photon scattering.

hep-ph↗

arXiv2015

Vacuum high harmonic generation in the shock regime

Electrodynamics becomes nonlinear and permits the self-interaction of fields when the quantised nature of vacuum states is taken into account. The effect on a plane probe pulse propagating through a stronger constant crossed background is calculated using numerical simulation and by analytically solving the corresponding wave equation. The electromagnetic shock resulting from vacuum high harmonic generation is investigated and a nonlinear shock parameter identified.

physics.plasm-ph↗

arXiv2015

Interaction of photons traversing a slowly varying electromagnetic background

When two electromagnetic fields counterpropagate, they are modified due to mutual interaction via the polarised virtual electron-positron states of the vacuum. By studying how photon-photon scattering effects such as birefringence and four-wave mixing evolve as the fields pass through one another, we find a significant increase during overlap. The results have particular relevance for calculations based on a constant field background.

hep-ph↗

arXiv2015

A Storage Ring Experiment to Detect a Proton Electric Dipole Moment

A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of $10^{-29}e\cdot$cm by using polarized "magic" momentum $0.7$~GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the Standard Model at the scale of 3000~TeV.

physics.acc-ph↗

arXiv2014

Double Compton scattering in a constant crossed field

Two-photon emission of an electron in an electromagnetic plane wave of vanishing frequency is calculated. The unpolarised probability is split into a two-step process, which is shown to be exactly equal to an integration over polarised subprocesses, and a one-step process, which is found to be dominant over the formation length. The assumptions of neglecting spin and simultaneous emission, commonly used in numerical simulations, are discussed in light of these results.

hep-ph↗

arXiv2014

Testing numerical implementations of strong field electrodynamics

We test current numerical implementations of laser-matter interactions by comparison with exact analytical results. Focussing on photon emission processes, it is found that the numerics accurately reproduce analytical emission spectra in all considered regimes, except for the harmonic structures often singled out as the most significant high intensity/multi-photon effects. We find that this discrepancy originates in the use of the locally constant field approximation.

physics.plasm-ph↗