675 research outputs found
Gravitational energy of a magnetized Schwarzschild black hole - a teleparallel approach
We investigate the distribution of gravitational energy on the spacetime of a
Schwarzschild black hole immersed in a cosmic magnetic field. This is done in
the context of the {\it Teleparallel Equivalent of General Relativity}, which
is an alternative geometrical formulation of General Relativity, where gravity
is describe by a spacetime endowed with torsion, rather than curvature, with
the fundamental field variables being tetrads. We calculate the energy enclosed
by a two-surface of constant radius - in particular, the energy enclosed by the
event horizon of the black hole. In this case we find that the magnetic field
has the effect of increasing the gravitational energy as compared to the vacuum
Schwarzschild case. We also compute the energy (i) in the weak magnetic field
limit, (ii) in the limit of vanishing magnetic field, and (iii) in the absence
of the black hole. In all cases our results are consistent with what should be
expected on physical grounds.Comment: version to match the one to be published on General Relativity and
Gravitatio
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
On Special Re-quantization of a Black Hole
Quantized expressions for the gravitational energy and momentum are derived
from a linearized theory of teleparallel gravity. The derivation relies on a
second-quantization procedure that constructs annihilation and creation
operators for the graviton. The resulting gravitational field is a collection
of gravitons, each of which has precise energy and momentum. On the basis of
the weak-field approximation of Schwarzschild's solution, a new form for the
quantization of the mass of a black hole is derived.Comment: 4 page
On reference frames in spacetime and gravitational energy in freely falling frames
We consider the interpretation of tetrad fields as reference frames in
spacetime. Reference frames may be characterized by an antisymmetric
acceleration tensor, whose components are identified as the inertial
accelerations of the frame (the translational acceleration and the frequency of
rotation of the frame). This tensor is closely related to
gravitoelectromagnetic field quantities. We construct the set of tetrad fields
adapted to observers that are in free fall in the Schwarzschild spacetime, and
show that the gravitational energy-momentum constructed out of this set of
tetrad fields, in the framework of the teleparallel equivalent of general
relatrivity, vanishes. This result is in agreement with the principle of
equivalence, and may be taken as a condition for a viable definition of
gravitational energy.Comment: 19 pages, no figures, accepted by Classical and Quantum Gravit
General relativity on a null surface: Hamiltonian formulation in the teleparallel geometry
The Hamiltonian formulation of general relativity on a null surface is
established in the teleparallel geometry. No particular gauge conditons on the
tetrads are imposed, such as the time gauge condition. By means of a 3+1
decomposition the resulting Hamiltonian arises as a completely constrained
system. However, it is structurally different from the the standard
Arnowitt-Deser-Misner (ADM) type formulation. In this geometrical framework the
basic field quantities are tetrads that transform under the global SO(3,1) and
the torsion tensor.Comment: 15 pages, Latex, no figures, to appear in the Gen. Rel. Gra
Three-dimensional Dirac oscillator in a thermal bath
The thermal properties of the three-dimensional Dirac oscillator are
considered. The canonical partition function is determined, and the
high-temperature limit is assessed. The degeneracy of energy levels and their
physical implications on the main thermodynamic functions are analyzed,
revealing that these functions assume values greater than the one-dimensional
case. So that at high temperatures, the limit value of the specific heat is
three times bigger.Comment: 9 pages, 4 figures. Text improved, references added. Revised to match
accepted version in Europhysics Letters
Regular string-like braneworlds
In this work, we propose a new class of smooth thick string-like braneworld
in six dimensions. The brane exhibits a varying brane-tension and an
asymptotic behavior. The brane-core geometry is parametrized by the Bulk
cosmological constant, the brane width and by a geometrical deformation
parameter. The source satisfies the dominant energy condition for the
undeformed solution and has an exotic asymptotic regime for the deformed
solution. This scenario provides a normalized massless Kaluza-Klein mode for
the scalar, gravitational and gauge sectors. The near-brane geometry allows
massive resonant modes at the brane for the state and nearby the brane for
.Comment: 14 pages, 12 figures. Some modifications to match the published
version in EPJ
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