6,889 research outputs found
Particle energization through time-periodic helical magnetic fields
We solve for the motion of charged particles in a helical time-periodic ABC
(Arnold-Beltrami-Childress) magnetic field. The magnetic field lines of a
stationary ABC field with coefficients are chaotic, and we show that
the motion of a charged particle in such a field is also chaotic at late times
with positive Lyapunov exponent. We further show that in time-periodic ABC
fields, the kinetic energy of a charged particle can increase indefinitely with
time. At late times the mean kinetic energy grows as a power law in time with
an exponent that approaches unity. For an initial distribution of particles,
whose kinetic energy is uniformly distributed within some interval, the PDF of
kinetic energy is, at late times, close to a Gaussian but with steeper tails.Comment: uses Revtex 4 instead of Revtex 4-
Exact three dimensional black hole with gauge fields in string theory
We have obtained exact three dimensional BTZ type solutions with gauge
fields, for string theory on a gauge symmetric gravitational background
constructed from semi-simple extension of the Poincare algebra (and the Maxwell
algebra) in 2 + 1 dimensions. We have studied the models for two non-Abelian
and Abelian gauge fields solutions and shown that the related sigma models for
each of these backgrounds is a SL(2;R) WZW (Wess-Zumino-Witten) model and that
they are classically canonically equivalent. We have also obtained the dual
solution for the Abelian case and by interpreting the new field strength
tensors of the Abelian solution as electromagnetic field strength tensors shown
that dual models coincide with the charged black string solution.Comment: 11 pages. Appendix and two references are adde
Conformal Invariance and Electrodynamics: Applications and General Formalism
The role of the conformal group in electrodynamics in four space-time
dimensions is re-examined. As a pedagogic example we use the application of
conformal transformations to find the electromagnetic field for a charged
particle moving with a constant relativistic acceleration from the Coulomb
electric field for the particle at rest. We also re-consider the reformulation
of Maxwell's equations on the projective cone, which is isomorphic to a
conformal compactification on Minkowski space, so that conformal
transformations, belonging to the group O(4,2), are realised linearly. The
resulting equations are different from those postulated previously and respect
additional gauge invariances which play an essential role in ensuring
consistency with conventional electrodynamics on Minkowski space. The solution
on the projective cone corresponding to a constantly accelerating charged
particle is discussed.Comment: 24 pages, 1 figure, plain tex, uses harvmac, eps
Gravitational non-commutativity and G\"odel-like spacetimes
We derive general conditions under which geodesics of stationary spacetimes
resemble trajectories of charged particles in an electromagnetic field. For
large curvatures (analogous to strong magnetic fields), the quantum
mechanicical states of these particles are confined to gravitational analogs of
{\it lowest Landau levels}. Furthermore, there is an effective
non-commutativity between their spatial coordinates. We point out that the
Som-Raychaudhuri and G\"odel spacetime and its generalisations are precisely of
the above type and compute the effective non-commutativities that they induce.
We show that the non-commutativity for G\"odel spacetime is identical to that
on the fuzzy sphere. Finally, we show how the star product naturally emerges in
Som-Raychaudhuri spacetimes.Comment: Two sections added (Relation to the fuzzy sphere, Emergence of the
star product). 10 pages, Revtex. To appear in General Relativity and
Gravitatio
Three Dimensional Pseudo-Spectral Compressible Magnetohydrodynamic GPU Code for Astrophysical Plasma Simulation
This paper presents the benchmarking and scaling studies of a GPU accelerated
three dimensional compressible magnetohydrodynamic code. The code is developed
keeping an eye to explain the large and intermediate scale magnetic field
generation is cosmos as well as in nuclear fusion reactors in the light of the
theory given by Eugene Newman Parker. The spatial derivatives of the code are
pseudo-spectral method based and the time solvers are explicit. GPU
acceleration is achieved with minimal code changes through OpenACC
parallelization and use of NVIDIA CUDA Fast Fourier Transform library (cuFFT).
NVIDIAs unified memory is leveraged to enable over-subscription of the GPU
device memory for seamless out-of-core processing of large grids. Our
experimental results indicate that the GPU accelerated code is able to achieve
upto two orders of magnitude speedup over a corresponding OpenMP parallel, FFTW
library based code, on a NVIDIA Tesla P100 GPU. For large grids that require
out-of-core processing on the GPU, we see a 7x speedup over the OpenMP, FFTW
based code, on the Tesla P100 GPU. We also present performance analysis of the
GPU accelerated code on different GPU architectures - Kepler, Pascal and Volta
Killing tensors and a new geometric duality
We present a theorem describing a dual relation between the local geometry of
a space admitting a symmetric second-rank Killing tensor, and the local
geometry of a space with a metric specified by this Killing tensor. The
relation can be generalized to spinning spaces, but only at the expense of
introducing torsion. This introduces new supersymmetries in their geometry.
Interesting examples in four dimensions include the Kerr-Newman metric of
spinning black-holes and self-dual Taub-NUT.Comment: 20 pages (a4), standard LaTeX, no figure
Electroelasticity of Charged Black Branes
We present the first-order corrected dynamics of fluid branes carrying
higher-form charge by obtaining the general form of their equations of motion
to pole-dipole order. Assuming linear response theory, we characterize the
corresponding effective theory of stationary bent charged (an)isotropic fluid
branes in terms of two sets of response coefficients, the Young modulus and the
piezoelectric moduli. We subsequently find large classes of examples in gravity
of this effective theory, by constructing stationary strained charged black
brane solutions to first order in a derivative expansion. Using solution
generating techniques and bent neutral black branes as a seed solution, we
obtain a class of charged black brane geometries carrying smeared Maxwell
charge in Einstein-Maxwell-dilaton gravity. In the specific case of
ten-dimensional space-time we furthermore use T-duality to generate bent black
branes with higher-form charge, including smeared D-branes of type II string
theory. By subsequently measuring the bending moment and the electric dipole
moment which these geometries acquire due to the strain, we uncover that their
form is captured by classical electroelasticity theory. In particular, we find
that the Young modulus and the piezoelectric moduli of our strained charged
black brane solutions are parameterized by a total of 4 response coefficients,
both for the isotropic as well as anisotropic cases.Comment: v2: 40pp; typos fixe
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