David A. Burton

Aspects of electromagnetic radiation reaction in strong fields

With the recent advances in laser technology, experimental investigation of radiation reaction phenomena is at last becoming a realistic prospect. A pedagogical introduction to electromagnetic radiation reaction is given, with the emphasis on matter driven by ultra-intense lasers. Single-particle, multi-particle, classical and quantum aspects are all addressed.

Asymptotic analysis of ultra-relativistic charge

This article offers a new approach for analysing the dynamic behaviour of distributions of charged particles in an electromagnetic field. After discussing the limitations inherent in the Lorentz–Dirac equation for a single point particle a simple model is proposed for a charged continuum interacting self-consistently with the Maxwell field in vacuo. The model is developed using intrinsic tensor field theory and exploits to the full the symmetry and light-cone structure of Minkowski spacetime. This permits the construction of a regular stress-energy tensor whose vanishing divergence determines a system of non-linear partial differential equations for the velocity and self-fields of accelerated charge. Within this covariant framework a particular perturbation scheme is motivated by an exact class of solutions to this system describing the evolution of a charged fluid under the combined effects of both self and external electromagnetic fields. The scheme yields an asymptotic approximation in terms of inhomogeneous linear equations for the self-consistent Maxwell field, charge current and time-like velocity field of the charged fluid and is defined as an ultra-relativistic configuration. To facilitate comparisons with existing accounts of beam dynamics an appendix translates the tensor formulation of the perturbation scheme into the language involving electric and magnetic fields observed in a laboratory (inertial) frame.

A kinetic model of radiating electrons

A kinetic theory is developed to describe radiating electrons whose motion is governed by the Lorentz-Dirac equation. This gives rise to a generalized Vlasov equation coupled to an equation for the evolution of the physical submanifold of phase space. The pathological solutions of the 1-particle theory may be removed by expanding the latter equation in powers of τ ≔ q 2/6πm. The radiation-induced change in entropy is explored and its physical origin is discussed. As a simple demonstration of the theory, the radiative damping rate of longitudinal plasma waves is calculated.

On the entropy of radiation reaction

Article history: The inexorable development of ever more powerful laser systems has re-ignited interest in electro- magnetic radiation reaction and its significance for the collective behavior of charged matter interact- ing with intense electromagnetic fields. The classical radiation reaction force on a point electron is non-conservative, and this has led some authors to question the validity of methods used to model ultra-intense laser-matter interactions including radiation reaction. We explain why such concern is un- warranted.

Twisted electromagnetic modes and Sagnac ring lasers

A new approximation scheme, designed to solve the covariant Maxwell equations inside a rotating hollow slender cavity (modelling a ring laser), is constructed. It is shown that for well-defined conditions there exist TE and TM modes with respect to the longitudinal axis of the cavity. A twisted mode spectrum is found to depend on the integrated Frenet torsion of the cavity and this in turn may affect the Sagnac beat frequency induced by a non-zero rotation of the cavity. The analysis is motivated by attempts to use ring lasers to measure terrestrial gravito-magnetism or the Lense–Thirring effect produced by the rotation of the earth.

Spinning particles in scalar-tensor gravity

We develop a new model of a spinning particle in Brans–Dicke spacetime using a metric-compatible connection with torsion. The particles spin vector is shown to be Fermi-parallel (by the Levi-Civita connection) along its worldline (an autoparallel of the metric-compatible connection) when neglecting spin-curvature coupling.

Dynamical model of Cosserat nanotubes

A Cosserat shell model of a single-wall carbon nanotube is developed based a recent static Cosserat rod model with microstructure. The new dynamical theory is used to study longitudinal acoustic phonon propagation.

Critical Dynamics of a Superelastic Network

Numerical results are presented for the dynamical properties of a superelastic, central force, triangular network. A negative eigenvalue theorem is employed to compute the integrated density of states of the network in a strip configuration and finite-size scaling is used to obtain accurate values for the critical exponents. The rigidity percolation threshold is found to be Pce = 0.6375 ± 0.0025. The ratio of the elastic modulus and correlation length exponents is found to be τ/ν = 1.00 ± 0.05 and the critical fracton dimensionality is = 4.0 ± 0.2.

Plasma-based wakefield accelerators as sources of axion-like particles

We estimate the average flux density of minimally-coupled axion-like particles generated by a laser-driven plasma wakefield propagating along a constant strong magnetic field. Our calculations suggest that a terrestrial source based on this approach could generate a pulse of axion-like particles whose flux density is comparable to that of solar axion-like particles at Earth. This mechanism is optimal for axion-like particles with mass in the range of interest of contemporary experiments designed to detect dark matter using microwave cavities.

Critical dynamics of a dilute central force network with partial bond bending forces

Numerical results are presented for the dynamical properties of a dilute, central force, triangular network with 60 degrees bond bending forces. The rigidity percolation threshold PR for such a network lies between the connectivity percolation threshold and the central force rigidity percolation threshold. A LU factorisation technique is used to determine the eigenvalues of the dynamical matrix and the results combined with finite size scaling to yield values for PR and the fracton dimensionality d of 0.40<or=PR<or=0.405 and 1.25<or=d<or=1.3.