857 research outputs found
Sparling two-forms, the conformal factor and the gravitational energy density of the teleparallel equivalent of general relativity
It has been shown recently that within the framework of the teleparallel
equivalent of general relativity (TEGR) it is possible to define the energy
density of the gravitational field. The TEGR amounts to an alternative
formulation of Einstein's general relativity, not to an alternative gravity
theory. The localizability of the gravitational energy has been investigated in
a number of space-times with distinct topologies, and the outcome of these
analises agree with previously known results regarding the exact expression of
the gravitational energy, and/or with the specific properties of the space-time
manifold. In this article we establish a relationship between the expression
for the gravitational energy density of the TEGR and the Sparling two-forms,
which are known to be closely connected with the gravitational energy. We also
show that our expression of energy yields the correct value of gravitational
mass contained in the conformal factor of the metric field.Comment: 12 pages, Latex file, no figures, to be published in Gen. Rel. Gra
Neutron Stars in Teleparallel Gravity
In this paper we deal with neutron stars, which are described by a perfect
fluid model, in the context of the teleparallel equivalent of general
relativity. We use numerical simulations to find the relationship between the
angular momentum of the field and the angular momentum of the source. Such a
relation was established for each stable star reached by the numerical
simulation once the code is fed with an equation of state, the central energy
density and the ratio between polar and equatorial radii. We also find a regime
where linear relation between gravitational angular momentum and moment of
inertia (as well as angular velocity of the fluid) is valid. We give the
spatial distribution of the gravitational energy and show that it has a linear
dependence with the squared angular velocity of the source.Comment: 19 pages, 14 figures. arXiv admin note: text overlap with
arXiv:1206.331
Energy of general 4-dimensional stationary axisymmetric spacetime in the teleparallel geometry
The field equation with the cosmological constant term is derived and the
energy of the general 4-dimensional stationary axisymmetric spacetime is
studied in the context of the hamiltonian formulation of the teleparallel
equivalent of general relativity (TEGR). We find that, by means of the integral
form of the constraints equations of the formalism naturally without any
restriction on the metric parameters, the energy for the asymptotically flat/de
Sitter/Anti-de Sitter stationary spacetimes in the Boyer-Lindquist coordinate
can be expressed as . It is surprised to learn that the
energy expression is relevant to the metric components ,
and only. As examples, by using this formula
we calculate the energies of the Kerr-Newman (KN), Kerr-Newman Anti-de Sitter
(KN-AdS), Kaluza-Klein, and Cveti\v{c}-Youm spacetimes.Comment: 12 page
Graviton resonances on two-field thick branes
This work presents new results about the graviton massive spectrum in
two-field thick branes. Analyzing the massive spectra with a relative
probability method we have firstly showed the presence of resonance structures
and obtained a connection between the thickness of the defect and the lifetimes
of such resonances. We obtain another interesting results considering the
degenerate Bloch brane solutions. In these thick brane models, we have the
emergence of a splitting effect controlled by a degeneracy parameter. When the
degeneracy constant tends to a critical value, we have found massive resonances
to the gravitational field indicating the existence of modes highly coupled to
the brane. We also discussed the influence of the brane splitting effect over
the resonance lifetimes.Comment: 15 pages, 8 figure
Variations of the Energy of Free Particles in the pp-Wave Spacetimes
We consider the action of exact plane gravitational waves, or pp-waves, on
free particles. The analysis is carried out by investigating the variations of
the geodesic trajectories of the particles, before and after the passage of the
wave. The initial velocities of the particles are non-vanishing. We evaluate
numerically the Kinetic energy per unit mass of the free particles, and obtain
interesting, quasi-periodic behaviour of the variations of the Kinetic energy
with respect to the width of the gaussian that represents the wave.
The variation of the energy of the free particle is expected to be exactly
minus the variation of the energy of the gravitational field, and therefore
provides an estimation of the local variation of the gravitational energy. The
investigation is carried out in the context of short bursts of gravitational
waves, and of waves described by normalised gaussians, that yield impulsive
waves in a certain limit.Comment: 20 pages, 18 figures, further arguments supporting the localizability
of the gravitational energy are presented, published in Univers
On the Black Hole Acceleration in the C-metric Space-time
We consider the C-metric as a gravitational field configuration that
describes an accelerating black hole in the presence of a semi-infinite cosmic
string, along the accelerating direction. We adopt the expression for the
gravitational energy-momentum developed in the teleparallel equivalent of
general relativity (TEGR) and obtain a possible explanation for the
acceleration of the black hole. The gravitational energy enclosed by surfaces
of constant radius around the black hole is evaluated, and in particular the
energy contained within the gravitational horizon is obtained. This energy
turns out to be proportional to the square root of the area of the horizon. We
find that the gravitational energy of the semi-infinite cosmic string is
negative and dominant for large values of the radius of integration. This
negative energy may explain the acceleration of the black hole, that moves
towards regions of lower gravitational energy along the string.Comment: 24 pages, 4 figures. The article has been revised and simplified; two
paragraphs were added in section 5 regarding the notion and definition of
gravitational energ
Casimir-Yang-Mills wormholes in
This study presents new three-dimensional traversable wormhole solutions
sourced by the Casimir density and pressure related to the quantum vacuum
fluctuations in Yang-Mills theory. First, we analyze the noninteracting Casimir
effect with an arbitrary state parameter and determine a simple
constant wormhole shape function. We introduce a new methodology for deforming
the state parameter and find well-behaved redshift functions. The wormhole can
be interpreted as a legitimate Casimir wormhole with an expected average state
parameter of . Then, we investigate the curvature properties, energy
conditions, and stability of the wormholes, finding that they are stable only
if the radius exceeds a specific value near the throat. Furthermore, we
discover a new family of traversable wormhole solutions sourced by the quantum
vacuum fluctuations of interacting (confined) Yang-Mills fields with a more
complex shape function. Deforming the effective state parameter similarly, we
obtain well-behaved redshift functions and wormhole solutions that depend on
relevant parameters of the system. Notably, higher string tension results in a
larger throat radius, potentially driven by an attempt to deconfine gluons and
stretch the wormhole.Comment: 20 pages, 8 figure
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