9 research outputs found
Torsion nonminimally coupled to the electromagnetic field and birefringence
In conventional Maxwell--Lorentz electrodynamics, the propagation of light is
influenced by the metric, not, however, by the possible presence of a torsion
T. Still the light can feel torsion if the latter is coupled nonminimally to
the electromagnetic field F by means of a supplementary Lagrangian of the type
l^2 T^2 F^2 (l = coupling constant). Recently Preuss suggested a specific
nonminimal term of this nature. We evaluate the spacetime relation of Preuss in
the background of a general O(3)-symmetric torsion field and prove by
specifying the optical metric of spacetime that this can yield birefringence in
vacuum. Moreover, we show that the nonminimally coupled homogeneous and
isotropic torsion field in a Friedmann cosmos affects the speed of light.Comment: Revtex, 12 pages, no figure
Invariant conserved currents in gravity theories: diffeomorphisms and local gauge symmetries
Previously, we have developed a general method to construct invariant
conserved currents and charges in gravitational theories with Lagrangians that
are invariant under spacetime diffeomorphisms and local Lorentz
transformations. This approach is now generalized to the case when the local
Lorentz group is replaced by an arbitrary local gauge group. The particular
examples include the Maxwell and Yang-Mills fields coupled to gravity with
Abelian and non-Abelian local internal symmetries, and the metric-affine
gravity in which the local Lorentz spacetime group is extended to the local
general linear group.Comment: 28 pages, Revte
Covariance properties and regularization of conserved currents in tetrad gravity
We discuss the properties of the gravitational energy-momentum 3-form within
the tetrad formulation of general relativity theory. We derive the covariance
properties of the quantities describing the energy-momentum content under
Lorentz transformations of the tetrad. As an application, we consider the
computation of the total energy (mass) of some exact solutions of Einstein's
general relativity theory which describe compact sources with asymptotically
flat spacetime geometry. As it is known, depending on the choice of tetrad
frame, the formal total integral for such configurations may diverge. We
propose a natural regularization method which yields finite values for the
total energy-momentum of the system and demonstrate how it works on a number of
explicit examples.Comment: 36 pages, Revtex, no figures; small changes, published versio
Wave propagation in linear electrodynamics
The Fresnel equation governing the propagation of electromagnetic waves for
the most general linear constitutive law is derived. The wave normals are found
to lie, in general, on a fourth order surface. When the constitutive
coefficients satisfy the so-called reciprocity or closure relation, one can
define a duality operator on the space of the two-forms. We prove that the
closure relation is a sufficient condition for the reduction of the fourth
order surface to the familiar second order light cone structure. We finally
study whether this condition is also necessary.Comment: 13 pages. Phys. Rev. D, to appea
On the energy transported by exact plane gravitational-wave solutions
The energy and momentum transported by exact plane gravitational-wave
solutions of Einstein equations are computed using the teleparallel equivalent
formulation of Einstein's theory. It is shown that these waves transport
neither energy nor momentum. A comparison with the usual linear plane
gravitational-waves solution of the linearized Einstein equation is presented.Comment: 15 pages, Revtex, no figures, to appear in Class. Quantum Gra