1,509 research outputs found
Signatures of Radiation Reaction in Ultra-Intense Laser Fields
We discuss radiation reaction effects on charges propagating in ultra-intense
laser fields. Our analysis is based on an analytic solution of the
Landau-Lifshitz equation. We suggest to measure radiation reaction in terms of
a symmetry breaking parameter associated with the violation of null translation
invariance in the direction opposite to the laser beam. As the Landau-Lifshitz
equation is nonlinear the energy transfer within the pulse is rather sensitive
to initial conditions. This is elucidated by comparing colliding and fixed
target modes in electron laser collisions.Comment: 8 pages, 6 figure
Persistent correlation of constrained colloidal motion
We have investigated the motion of a single optically trapped colloidal
particle close to a limiting wall at time scales where the inertia of the
surrounding fluid plays a significant role. The velocity autocorrelation
function exhibits a complex interplay due to the momentum relaxation of the
particle, the vortex diffusion in the fluid, the obstruction of flow close to
the interface, and the harmonic restoring forces due to the optical trap. We
show that already a weak trapping force has a significant impact on the
velocity autocorrelation function C(t)= at times where the
hydrodynamic memory leads to an algebraic decay. The long-time behavior for the
motion parallel and perpendicular to the wall is derived analytically and
compared to numerical results. Then, we discuss the power spectral densities of
the displacement and provide simple interpolation formulas. The theoretical
predictions are finally compared to recent experimental observations.Comment: 12 pages, 6 figure
Lorentzian regularization and the problem of point-like particles in general relativity
The two purposes of the paper are (1) to present a regularization of the
self-field of point-like particles, based on Hadamard's concept of ``partie
finie'', that permits in principle to maintain the Lorentz covariance of a
relativistic field theory, (2) to use this regularization for defining a model
of stress-energy tensor that describes point-particles in post-Newtonian
expansions (e.g. 3PN) of general relativity. We consider specifically the case
of a system of two point-particles. We first perform a Lorentz transformation
of the system's variables which carries one of the particles to its rest frame,
next implement the Hadamard regularization within that frame, and finally come
back to the original variables with the help of the inverse Lorentz
transformation. The Lorentzian regularization is defined in this way up to any
order in the relativistic parameter 1/c^2. Following a previous work of ours,
we then construct the delta-pseudo-functions associated with this
regularization. Using an action principle, we derive the stress-energy tensor,
made of delta-pseudo-functions, of point-like particles. The equations of
motion take the same form as the geodesic equations of test particles on a
fixed background, but the role of the background is now played by the
regularized metric.Comment: 34 pages, to appear in J. Math. Phy
Magnetic mirror cavities as THz radiation sources and a means of quantifying radiation friction
We propose a radiation source based on a magnetic mirror cavity. Relativistic
electrons are simulated entering the cavity and their trajectories and
resulting emission spectra are calculated. The uniformity of the particle
orbits is found to result in a frequency comb in terahertz range, the precise
energies of which are tuneable by varying the electron's -factor. For
very high energy particles radiation friction causes the spectral harmonics to
broaden and we suggest this as a possible way to verify competing classical
equations of motion.Comment: 8 pages, 10 figure
Observation of light dragging in rubidium vapor cell
We report on the experimental demonstration of light dragging effect due to
atomic motion in a rubidium vapor cell. We found that the minimum group
velocity is achieved for light red-shifted from the center of the atomic
resonance, and that the value of this shift increases with decreasing group
velocity, in agreement with the theoretical predictions by Kocharovskaya,
Rostovtsev, and Scully [Phys. Rev. Lett. {\bf 86}, 628 (2001)].Comment: 4 pages 4 figures, submitted to PR
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
Strong signatures of radiation reaction below the radiation dominated regime
The influence of radiation reaction (RR) on multiphoton Thomson scattering by
an electron colliding head-on with a strong laser beam is investigated in a new
regime, in which the momentum transferred on average to the electron by the
laser pulse approximately compensates the one initially prepared. This
equilibrium is shown to be far more sensitive to the influence of RR than
previously studied scenarios. As a consequence RR can be experimentally
investigated with currently available laser systems and the underlying widely
discussed theoretical equations become testable for the first time.Comment: 4 pages, 3 figure
The Ubiquitous 'c': from the Stefan-Boltzmann Law to Quantum Information
I discuss various aspects of the role of the conformal anomaly number c in 2-
and 1+1-dimensional critical behaviour: its appearance as the analogue of
Stefan's constant, its fundamental role in conformal field theory, in the
classification of 2d universality classes, and as a measure of quantum
entanglement, among other topics.Comment: 8 pages, 2 figures. Boltzmann Medal Lecture, Statphys24, Cairns 2010.
v3: minor revision
Third post-Newtonian dynamics of compact binaries: Noetherian conserved quantities and equivalence between the harmonic-coordinate and ADM-Hamiltonian formalisms
A Lagrangian from which derive the third post-Newtonian (3PN) equations of
motion of compact binaries (neglecting the radiation reaction damping) is
obtained. The 3PN equations of motion were computed previously by Blanchet and
Faye in harmonic coordinates. The Lagrangian depends on the harmonic-coordinate
positions, velocities and accelerations of the two bodies. At the 3PN order,
the appearance of one undetermined physical parameter \lambda reflects an
incompleteness of the point-mass regularization used when deriving the
equations of motion. In addition the Lagrangian involves two unphysical
(gauge-dependent) constants r'_1 and r'_2 parametrizing some logarithmic terms.
The expressions of the ten Noetherian conserved quantities, associated with the
invariance of the Lagrangian under the Poincar\'e group, are computed. By
performing an infinitesimal ``contact'' transformation of the motion, we prove
that the 3PN harmonic-coordinate Lagrangian is physically equivalent to the 3PN
Arnowitt-Deser-Misner Hamiltonian obtained recently by Damour, Jaranowski and
Sch\"afer.Comment: 30 pages, to appear in Classical and Quantum Gravit
Gravitation, electromagnetism and the cosmological constant in purely affine gravity
The Eddington Lagrangian in the purely affine formulation of general
relativity generates the Einstein equations with the cosmological constant. The
Ferraris-Kijowski purely affine Lagrangian for the electromagnetic field, which
has the form of the Maxwell Lagrangian with the metric tensor replaced by the
symmetrized Ricci tensor, is dynamically equivalent to the Einstein-Maxwell
Lagrangian in the metric formulation. We show that the sum of the two affine
Lagrangians is dynamically inequivalent to the sum of the analogous Lagrangians
in the metric-affine/metric formulation. We also show that such a construction
is valid only for weak electromagnetic fields. Therefore the purely affine
formulation that combines gravitation, electromagnetism and the cosmological
constant cannot be a simple sum of terms corresponding to separate fields.
Consequently, this formulation of electromagnetism seems to be unphysical,
unlike the purely metric and metric-affine pictures, unless the electromagnetic
field couples to the cosmological constant.Comment: 14 pages, extended and combined with gr-qc/0701176; published versio
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