7,325 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
A Deep Optical Observation for an Enigmatic Unidentified Gamma-Ray Source 3EG J1835+5918
We report a deep optical imaging observation by the Subaru telescope for a
very soft X-ray source RX J1836.2+5925, which has been suspected to be an
isolated neutron star associated with the brightest as-yet unidentified EGRET
source outside the Galactic plane, 3EG J1835+5918. An extended source having a
complex, bipolar shape is found at B ~ 26, and this might be an extended pulsar
nebular whose flux is about 5-6 orders of magnitude lower than gamma-ray flux,
although finding a galaxy of this magnitude by chance in the error circle is of
order unity. We have found two even fainter, possibly point sources at B ~ 28,
although their detections are not firm because of low signal-to-noise. If the
extended object of B ~ 26 is a galaxy and not related to 3EG J1835+5918, a
lower limit on X-ray/optical flux ratio is set as f_X/f_B >~ 2700, giving a
further strong support of the neutron-star identification of 3EG J1835+5918.
Interestingly, if either of the two sources at B ~ 28 is the real counterpart
of RX J1836.2+5925 and thermal emission from the surface of an isolated neutron
star, the temperature and distance to the source become ~ 4 x 10^5K and ~300pc,
respectively, showing a striking similarity of its spectral energy distribution
to the proto-type radio-quiet gamma-ray pulsar Geminga. No detection of
nonthermal hard X-ray emission is consistent with the ASCA upper limit, if the
nonthermal flux of 3EG J1835+5918/RX J1836.2+5925 is at a similar level with
that of Gemiga.Comment: PASJ Letters in press. (Received March 26; Accepted May 17
Heisenberg and Modular Invariance of N=2 Conformal Field Theory
We present a theta function representation of the twisted characters for the
rational N=2 superconformal field theory, and discuss the Jacobi-form like
functional properties of these characters for a fixed central charge under the
action of a finite Heisenberg group and modular transformations.Comment: 21 pages, Latex, 1 figure; minor typos corrected--Journal versio
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
Preheating after N-flation
We study preheating in N-flation, assuming the Mar\v{c}enko-Pastur mass
distribution, equal energy initial conditions at the beginning of inflation and
equal axion-matter couplings, where matter is taken to be a single, massless
bosonic field. By numerical analysis we find that preheating via parametric
resonance is suppressed, indicating that the old theory of perturbative
preheating is applicable. While the tensor-to-scalar ratio, the non-Gaussianity
parameters and the scalar spectral index computed for N-flation are similar to
those in single field inflation (at least within an observationally viable
parameter region), our results suggest that the physics of preheating can
differ significantly from the single field case.Comment: 14 pages, 14 figures, references added, fixed typo
XMM-Newton observations of the eastern jet of SS433
The radio supernova remnant W50 hosts at its center the peculiar galactic
X-ray binary SS 433. It shows a central spherical structure with two `ears'
which are supposed to be formed by the interaction of the precessing jets of SS
433 with the supernova shell. In two pointings in September/October 2004 for 30
ks each the eastern jet of SS 433 was observed with XMM-Newton to study the
outermost parts of the `ear' and the X-ray bright emission region about 35
arcmin from SS 433. The spectra consist of two components: a non-thermal power
law with photon index \Gamma ~ 2.17+/-0.02 and a thermal component at a typical
temperature of kT ~ 0.3 keV. The X-ray emission seems to fill the whole
interior region of the radio remnant W50. The jet terminates in the eastern
`ear' in a ring-like terminal shock which indicates a flow with a kind of
hollow-cone morphology. The spatial coincidence of X-ray and radio emission
suggests physical conditions similar to those found at the outer shocks of
ordinary supernova remnants. The bright emission region closer to SS 433
radiates non-thermally in a spatially well confined geometry at higher X-ray
energies. At soft X-rays the shape of the region gets blurred, centered on the
hard lenticular emission. The shape of this region and the bend in the jet
propagation direction might be caused by the interaction of a re-collimated jet
with the outer, non homogeneous interstellar matter distribution. The physical
conditions leading to the re-collimation of the jet and the peculiar emission
morphology are far from being understood and require deeper observations as
well as a detailed modeling of the interaction of a jet with its surroundings.Comment: 10 pages, 8 figures, to appear in A&
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