96 research outputs found
Bergmann-Thomson energy-momentum complex for solutions more general than the Kerr-Schild class
In a very well-known paper, Virbhadra's research group proved that the
Weinberg, Papapetrou, Landau and Lifshitz, and Einstein energy-momentum
complexes ``coincide'' for all metrics of Kerr-Schild class. A few years later,
Virbhadra clarified that this ``coincidence'' in fact holds for metrics more
general than the Kerr-Schild class. In the present paper, this study is
extended for the Bergmann-Thomson complex and it is proved that this complex
also ``coincides'' with those complexes for a more general than the Kerr-Schild
class metric.Comment: RevTex, 12 page
Energy and momentum of Bianchi Type VI_h Universes
We obtain the energy and momentum of the Bianchi type VI_h universes using
different prescriptions for the energy-momentum complexes in the framework of
general relativity. The energy and momentum of the Bianchi VI_h universe are
found to be zero for the parameter h = -1 of the metric. The vanishing of these
results support the conjecture of Tryon that Universe must have a zero net
value for all conserved quantities.This also supports the work of Nathan Rosen
with the Robertson-Walker metric. Moreover, it raises an interesting question:
"Why h=-1 case is so special?
Energy Distribution of a Stationary Beam of Light
Aguirregabiria et al showed that Einstein, Landau and Lifshitz, Papapetrou,
and Weinberg energy-momentum complexes coincide for all Kerr-Schild metric.
Bringely used their general expression of the Kerr-Schild class and found
energy and momentum densities for the Bonnor metric. We obtain these results
without using Aguirregabiria et al results and verify that Bringley's results
are correct. This also supports Aguirregabiria et al results as well as
Cooperstock hypothesis. Further, we obtain the energy distribution of the
space-time under consideration.Comment: Latex, no figures [Admin note: substantial overlap with gr-qc/9910015
and hep-th/0308070
InxGa1-xP Nanowire Growth Dynamics Strongly Affected by Doping Using Diethylzinc
Semiconductor nanowires are versatile building blocks for optoelectronic devices, in part because nanowires offer an increased freedom in material design due to relaxed constraints on lattice matching during the epitaxial growth. This enables the growth of ternary alloy nanowires in which the bandgap is tunable over a large energy range, desirable for optoelectronic devices. However, little is known about the effects of doping in the ternary nanowire materials, a prerequisite for applications. Here we present a study of p-doping of InxGa1-xP nanowires and show that the growth dynamics are strongly affected when diethylzinc is used as a dopant precursor. Specifically, using in situ optical reflectometry and high-resolution transmission electron microscopy we show that the doping results in a smaller nanowire diameter, a more predominant zincblende crystal structure, a more Ga-rich composition, and an increased axial growth rate. We attribute these effects to changes in seed particle wetting angle and increased TMGa pyrolysis efficiency upon introducing diethylzinc. Lastly, we demonstrate degenerate p-doping levels in InxGa1-xP nanowires by the realization of an Esaki tunnel diode. Our findings provide insights into the growth dynamics of ternary alloy nanowires during doping, thus potentially enabling the realization of such nanowires with high compositional homogeneity and controlled doping for high-performance optoelectronics devices
Teleparallel Energy-Momentum Distribution of Static Axially Symmetric Spacetimes
This paper is devoted to discuss the energy-momentum for static axially
symmetric spacetimes in the framework of teleparallel theory of gravity. For
this purpose, we use the teleparallel versions of Einstein, Landau-Lifshitz,
Bergmann and Mller prescriptions. A comparison of the results shows
that the energy density is different but the momentum turns out to be constant
in each prescription. This is exactly similar to the results available in
literature using the framework of General Relativity. It is mentioned here that
Mller energy-momentum distribution is independent of the coupling
constant . Finally, we calculate energy-momentum distribution for the
Curzon metric, a special case of the above mentioned spacetime.Comment: 14 pages, accepted for publication in Mod. Phys. Lett.
Energy Distribution associated with Static Axisymmetric Solutions
This paper has been addressed to a very old but burning problem of energy in
General Relativity. We evaluate energy and momentum densities for the static
and axisymmetric solutions. This specializes to two metrics, i.e., Erez-Rosen
and the gamma metrics, belonging to the Weyl class. We apply four well-known
prescriptions of Einstein, Landau-Lifshitz, Papaterou and Mller to
compute energy-momentum density components. We obtain that these prescriptions
do not provide similar energy density, however momentum becomes constant in
each case. The results can be matched under particular boundary conditions.Comment: 18 pages, accepted for publication in Astrophysics and SpaceScienc
Energy and Momentum densities of cosmological models, with equation of state , in general relativity and teleparallel gravity
We calculated the energy and momentum densities of stiff fluid solutions,
using Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum complexes,
in both general relativity and teleparallel gravity. In our analysis we get
different results comparing the aforementioned complexes with each other when
calculated in the same gravitational theory, either this is in general
relativity and teleparallel gravity. However, interestingly enough, each
complex's value is the same either in general relativity or teleparallel
gravity. Our results sustain that (i) general relativity or teleparallel
gravity are equivalent theories (ii) different energy-momentum complexes do not
provide the same energy and momentum densities neither in general relativity
nor in teleparallel gravity. In the context of the theory of teleparallel
gravity, the vector and axial-vector parts of the torsion are obtained. We show
that the axial-vector torsion vanishes for the space-time under study.Comment: 15 pages, no figures, Minor typos corrected; version to appear in
International Journal of Theoretical Physic
Stable Magnetic Universes Revisited
A regular class of static, cylindrically symmetric pure magnetic field
metrics is rederived in a different metric ansatz in all dimensions. Radial,
time dependent perturbations show that for dimensions d>3 such spacetimes are
stable at both near r\approx0 and large radius r\rightarrow\infty. In a
different gauge these stability analysis and similar results were known
beforehand. For d=3, however, simultaneous stability requirement at both, near
and far radial distances can not be reconciled for time - dependent
perturbations. Restricted, numerical geodesics for neutral particles reveal a
confinement around the center in the polar plane. Charged, time-like geodesics
for d=4 on the other hand are shown numerically to run toward infinity.Comment: 11 pages, 3figure
Distribution of Energy-Momentum in a Schwarzschild-Quintessence Space-time Geometry
An analysis of the energy-momentum localization for a four-dimensional\break
Schwarzschild black hole surrounded by quintessence is presented in order to
provide expressions for the distributions of energy and momentum. The
calculations are performed by using the Landau-Lifshitz and Weinberg
energy-momentum complexes. It is shown that all the momenta vanish, while the
expression for the energy depends on the mass of the black hole, the state
parameter and the normalization factor . The special case of
is also studied, and two limiting cases are examined.Comment: 9 page
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