11,009 research outputs found
Energy-momentum and angular momentum densities in gauge theories of gravity
In the \bar{\mbox{\rm Poincar\'{e}}} gauge theory of gravity, which has
been formulated on the basis of a principal fiber bundle over the space-time
manifold having the covering group of the proper orthochronous Poincar\'{e}
group as the structure group, we examine the tensorial properties of the
dynamical energy-momentum density and the ` `
spin" angular momentum density of the
gravitational field. They are both space-time vector densities, and transform
as tensors under {\em global} - transformations. Under {\em local}
internal translation, is invariant, while
transforms inhomogeneously. The dynamical
energy-momentum density and the ` ` spin"
angular momentum density of the matter field
are also examined, and they are known to be space-time vector densities and to
obey tensorial transformation rules under internal \bar{\mbox{\rm
Poincar\'{e}}} gauge transformations. The corresponding discussions in
extended new general relativity which is obtained as a teleparallel limit of
\bar{\mbox{\rm Poincar\'{e}}} gauge theory are also given, and
energy-momentum and ` ` spin" angular momentum densities are known to be well
behaved. Namely, they are all space-time vector densities, etc. In both
theories, integrations of these densities on a space-like surface give the
total energy-momentum and {\em total} (={\em spin}+{\em orbital}) angular
momentum for asymptotically flat space-time. The tensorial properties of
canonical energy-momentum and ` ` extended orbital angular momentum" densities
are also examined.Comment: 18 page
On Fractional Tempered Stable Motion
Fractional tempered stable motion (fTSm)} is defined and studied. FTSm has
the same covariance structure as fractional Brownian motion, while having tails
heavier than Gaussian but lighter than stable. Moreover, in short time it is
close to fractional stable L\'evy motion, while it is approximately fractional
Brownian motion in long time. A series representation of fTSm is derived and
used for simulation and to study some of its sample path properties.Comment: 25 pages, 6 figure
On Layered Stable Processes
Layered stable (multivariate) distributions and processes are defined and
studied. A layered stable process combines stable trends of two different
indices, one of them possibly Gaussian. More precisely, in short time, it is
close to a stable process while, in long time, it approximates another stable
(possibly Gaussian) process. We also investigate the absolute continuity of a
layered stable process with respect to its short time limiting stable process.
A series representation of layered stable processes is derived, giving insights
into both the structure of the sample paths and of the short and long time
behaviors. This series is further used for sample paths simulation.Comment: 22 pages, 9 figure
Jarzynski equality for the Jepsen gas
We illustrate the Jarzynski equality on the exactly solvable model of a
one-dimensional ideal gas in uniform expansion or compression. The analytical
results for the probability density of the work performed by the gas
are compared with the results of molecular dynamics simulations for a
two-dimensional dilute gas of hard spheres.Comment: 7 pages, 4 figures, submitted to Europhys. Let
Poincar\'{e} gauge theory of gravity
A Poincar\'{e} gauge theory of (2+1)-dimensional gravity is developed.
Fundamental gravitational field variables are dreibein fields and Lorentz gauge
potentials, and the theory is underlain with the Riemann-Cartan space-time. The
most general gravitational Lagrangian density, which is at most quadratic in
curvature and torsion tensors and invariant under local Lorentz transformations
and under general coordinate transformations, is given. Gravitational field
equations are studied in detail, and solutions of the equations for weak
gravitational fields are examined for the case with a static, \lq \lq spin"less
point like source. We find, among other things, the following: (1)Solutions of
the vacuum Einstein equation satisfy gravitational field equations in the
vacuum in this theory. (2)For a class of the parameters in the gravitational
Lagrangian density, the torsion is \lq \lq frozen" at the place where \lq \lq
spin" density of the source field is not vanishing. In this case, the field
equation actually agrees with the Einstein equation, when the source field is
\lq \lq spin"less. (3)A teleparallel theory developed in a previous paper is
\lq \lq included as a solution" in a limiting case. (4)A Newtonian limit is
obtainable, if the parameters in the Lagrangian density satisfy certain
conditions.Comment: 27pages, RevTeX, OCU-PHYS-15
Pulse Profile Change Possibly Associated with a Glitch in an Anomalous X-Ray Pulsar 4U 0142+61
We report a glitch-like pulse frequency deviation from the simple spin-down
law in an anomalous X-ray pulsar (AXP) 4U 0142+61 detected by ASCA
observations. We also found a significant pulse profile change after the
putative glitch. The glitch parameters resemble those found in another AXP 1RXS
J170849.0400910, in the Vela pulsar, and in other radio pulsars. This
suggests that the radio pulsars and AXPs have the same internal structure and
glitch mechanism. It must be noted, however, that the pulse frequency anomaly
can also be explained by a gradual change of the spin-down rate ()
without invoking a glitch.Comment: 14 pages, 4 figures, accepted by Ap
Quantum Electrodynamics at Large Distances II: Nature of the Dominant Singularities
Accurate calculations of macroscopic and mesoscopic properties in quantum
electrodynamics require careful treatment of infrared divergences: standard
treatments introduce spurious large-distances effects. A method for computing
these properties was developed in a companion paper. That method depends upon a
result obtained here about the nature of the singularities that produce the
dominant large-distance behaviour. If all particles in a quantum field theory
have non-zero mass then the Landau-Nakanishi diagrams give strong conditions on
the singularities of the scattering functions. These conditions are severely
weakened in quantum electrodynamics by effects of points where photon momenta
vanish. A new kind of Landau-Nakanishi diagram is developed here. It is geared
specifically to the pole-decomposition functions that dominate the macroscopic
behaviour in quantum electrodynamics, and leads to strong results for these
functions at points where photon momenta vanish.Comment: 40 pages, 11 encapsulated postscript figures, latexed,
math_macros.tex can be found on Archive. full postscript available from
http://theorl.lbl.gov/www/theorgroup/papers/35972.p
The Boundary Conformal Field Theories of the 2D Ising critical points
We present a new method to identify the Boundary Conformal Field Theories
(BCFTs) describing the critical points of the Ising model on the strip. It
consists in measuring the low-lying excitation energies spectra of its quantum
spin chain for different boundary conditions and then to compare them with
those of the different boundary conformal field theories of the
minimal model.Comment: 7 pages, no figures. Talk given at the XXth International Conference
on Integrable Systems and Quantum Symmetries (ISQS-20). Prague, June 201
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