260 research outputs found
Dirac spinor fields in the teleparallel gravity: comment on "Metric-affine approach to teleparallel gravity"
We show that the coupling of a Dirac spinor field with the gravitational
field in the teleparallel equivalent of general relativity is consistent. For
an arbitrary SO(3,1) connection there are two possibilities for the coupling of
the spinor field with the gravitational field. The problems of consistency
raised by Y. N. Obukhov and J. G. Pereira in the paper {\it Metric-affine
approach to teleparallel gravity} [gr-qc/0212080] take place only in the
framework of one particular coupling. By adopting an alternative coupling the
consistency problem disappears.Comment: 8 pages, Latex file, no figures, to appear in the Phys. Rev. D as a
Commen
Space-time defects and teleparallelism
We consider the class of space-time defects investigated by Puntigam and
Soleng. These defects describe space-time dislocations and disclinations
(cosmic strings), and are in close correspondence to the actual defects that
arise in crystals and metals. It is known that in such materials dislocations
and disclinations require a small and large amount of energy, respectively, to
be created. The present analysis is carried out in the context of the
teleparallel equivalent of general relativity (TEGR). We evaluate the
gravitational energy of these space-time defects in the framework of the TEGR
and find that there is an analogy between defects in space-time and in
continuum material systems: the total gravitational energy of space-time
dislocations and disclinations (considered as idealized defects) is zero and
infinit, respectively.Comment: 22 pages, no figures, to appear in the Class. Quantum Gravit
Lessons of spin and torsion: Reply to ``Consistent coupling to Dirac fields in teleparallelism"
In reply to the criticism made by Mielke in the pereceding Comment [Phys.
Rev. D69 (2004) 128501] on our recent paper, we once again explicitly
demonstrate the inconsistency of the coupling of a Dirac field to gravitation
in the teleparallel equivalent of general relativity. Moreover, we stress that
the mentioned inconsistency is generic for {\it all} sources with spin and is
by no means restricted to the Dirac field. In this sense the
-covariant generalization of the spinor fields in the teleparallel
gravity theory is irrelevant to the inconsistency problem.Comment: Revtex, 4 pages, no figure
Charged Dilaton, Energy, Momentum and Angular-Momentum in Teleparallel Theory Equivalent to General Relativity
We apply the energy-momentum tensor to calculate energy, momentum and
angular-momentum of two different tetrad fields. This tensor is coordinate
independent of the gravitational field established in the Hamiltonian structure
of the teleparallel equivalent of general relativity (TEGR). The spacetime of
these tetrad fields is the charged dilaton. Our results show that the energy
associated with one of these tetrad fields is consistent, while the other one
does not show this consistency. Therefore, we use the regularized expression of
the gravitational energy-momentum tensor of the TEGR. We investigate the energy
within the external event horizon using the definition of the gravitational
energy-momentum.Comment: 22 Pages Late
Energy and Angular Momentum Densities in a Godel-Type Universe in the Teleparallel Geometry
The main scope of this research consists in evaluating the energy-momentum
(gravitational field plus matter) and gravitational angular momentum densities
in the universe with global rotation, considering the Godel-Obukhov metric. For
this, we use the Hamiltonian formalism of the Teleparallel Equivalent of
General Relativity (TEGR), which is justified for presenting covariant
expressions for the considered quantities. We found that the total energy
density calculated by the TEGR method is in agreement with the results reported
by other authors in the literature using pseudotensors. The result found for
the angular momentum density depends on the rotational parameter as expected.
We also show explicitly the equivalence among the field equations of the TEGR
and Einstein equations (RG), considering a perfect fluid and Godel-Obukhov
metric.Comment: 20 pages, no figures. Revised in view of Referee's comments. Version
to appear in the Gravitation and Cosmolog
Teleparallel Versions of Friedmann and Lewis-Papapetrou Spacetimes
This paper is devoted to investigate the teleparallel versions of the
Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad
and the torsion fields for both the spacetimes. It is shown that the
axial-vector vanishes for the Friedmann models. We discuss the different
possibilities of the axial-vector depending on the arbitrary functions
and in the Lewis-Papapetrou metric. The vector related with spin has
also been evaluated.Comment: 13 pages, accepted for publication in GR
Torsion Gravity: a Reappraisal
The role played by torsion in gravitation is critically reviewed. After a
description of the problems and controversies involving the physics of torsion,
a comprehensive presentation of the teleparallel equivalent of general
relativity is made. According to this theory, curvature and torsion are
alternative ways of describing the gravitational field, and consequently
related to the same degrees of freedom of gravity. However, more general
gravity theories, like for example Einstein-Cartan and gauge theories for the
Poincare and the affine groups, consider curvature and torsion as representing
independent degrees of freedom. By using an active version of the strong
equivalence principle, a possible solution to this conceptual question is
reviewed. This solution favors ultimately the teleparallel point of view, and
consequently the completeness of general relativity. A discussion of the
consequences for gravitation is presented.Comment: RevTeX, 34 pages. Review article to be published by Int. J. Mod.
Phys.
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