29 research outputs found
Light propagation in generally covariant electrodynamics and the Fresnel equation
Within the framework of generally covariant (pre-metric) electrodynamics, we
specify a local vacuum spacetime relation between the excitation and the field strength . We study the propagation of
electromagnetic waves in such a spacetime by Hadamard's method and arrive, with
the constitutive tensor density , at a Fresnel
equation which is algebraic of 4th order in the wave covector. We determine how
the different pieces of , in particular the axion and the skewon
pieces, affect the propagation of light.Comment: 6 pages, uses ws-ijmpa.cls. Invited talk given at Journees
Relativistes, University College Dublin, Sept. 2001. Will appear in
Int.J.Mod.Phys.
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
On the theory of the skewon field: From electrodynamics to gravity
The Maxwell equations expressed in terms of the excitation and the field strength are metric-free and require an
additional constitutive law in order to represent a complete set of field
equations. In vacuum, we call this law the ``spacetime relation''. We assume it
to be local and linear. Then encompasses 36
permittivity/permeability functions characterizing the electromagnetic
properties of the vacuum. These 36 functions can be grouped into 20+15+1
functions. Thereof, 20 functions finally yield the dilaton field and the metric
of spacetime, 1 function represents the axion field, and 15 functions the
(traceless) skewon field \notS_i{}^j (S slash), with . The
hypothesis of the existence of \notS_i{}^j was proposed by three of us in
2002. In this paper we discuss some of the properties of the skewon field, like
its electromagnetic energy density, its possible coupling to Einstein-Cartan
gravity, and its corresponding gravitational energy.Comment: latex-file, 15 pages, 1 figur
An exact solution of the metric-affine gauge theory with dilation, shear, and spin charges
The spacetime of the metric-affine gauge theory of gravity (MAG) encompasses
{\it nonmetricity} and {\it torsion} as post-Riemannian structures. The sources
of MAG are the conserved currents of energy-momentum and dilation, shear and
spin. We present an exact static spherically symmetric vacuum solution of the
theory describing the exterior of a lump of matter carrying mass and dilation,
shear and spin charges.Comment: 13 pages, RevTe
Goedel type solution in teleparallel gravity
The stationary cosmological model without closed timelike curves of G\"odel
type is obtained for the ideal dust matter source within the framework of the
teleparallel gravity. For a specific choice of the teleparallel gravity
parameters, this solution reproduces the causality violating stationary G\"odel
solution in general relativity, in accordance with the teleparallel equivalent
of general relativity. The relation between the axial-vector torsion and the
cosmic vorticity is clarified.Comment: Revtex, 15 pages, no figures, to appear in Phys. Lett.
On optical black holes in moving dielectrics
We study the optical paths of the light rays propagating inside a nonlinear
moving dielectric media. For the rapidly moving dielectrics we show the
existence of a distinguished surface which resembles, as far as the light
propagation is concerned, the event horizon of a black hole. Our analysis
clarifies the physical conditions under which electromagnetic analogues of the
gravitational black holes can eventually be obtained in laboratory.Comment: 5 pages, 2 figures, revtex
Entropy Identity and Material-Independent Equilibrium Conditions in Relativistic Thermodynamics
On the basis of the balance equations for energy-momentum, spin, particle and
entropy density, an approach is considered which represents a comparatively
general framework for special- and general-relativistic continuum
thermodynamics. In the first part of the paper, a general entropy density
4-vector, containing particle, energy-momentum, and spin density contributions,
is introduced which makes it possible, firstly, to judge special assumptions
for the entropy density 4-vector made by other authors with respect to their
generality and validity and, secondly, to determine entropy supply and entropy
production. Using this entropy density 4-vector, in the second part,
material-independent equilibrium conditions are discussed. While in literature,
at least if one works in the theory of irreversible thermodynamics assuming a
Riemann space-time structure, generally thermodynamic equilibrium is determined
by introducing a variety of conditions by hand, the present approach proceeds
as follows: For a comparatively wide class of space-time geometries the
necessary equilibrium conditions of vanishing entropy supply and entropy
production are exploited and, afterwards, supplementary conditions are assumed
which are motivated by the requirement that thermodynamic equilibrium
quantities have to be determined uniquely.Comment: Research Paper, 30 page
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
The Spectral Action for Dirac Operators with skew-symmetric Torsion
We derive a formula for the gravitational part of the spectral action for
Dirac operators on 4-dimensional manifolds with totally anti-symmetric torsion.
We find that the torsion becomes dynamical and couples to the traceless part of
the Riemann curvature tensor. Finally we deduce the Lagrangian for the Standard
Model of particle physics in presence of torsion from the Chamseddine-Connes
Dirac operator.Comment: Longer introduction and conclusion adde
New Classes of Off-Diagonal Cosmological Solutions in Einstein Gravity
In this work, we apply the anholonomic deformation method for constructing
new classes of anisotropic cosmological solutions in Einstein gravity and/or
generalizations with nonholonomic variables. There are analyzed four types of,
in general, inhomogeneous metrics, defined with respect to anholonomic frames
and their main geometric properties. Such spacetimes contain as particular
cases certain conformal and/or frame transforms of the well known
Friedman-Robertson-Walker, Bianchi, Kasner and Godel universes and define a
great variety of cosmological models with generic off-diagonal metrics, local
anisotropy and inhomogeneity. It is shown that certain nonholonomic
gravitational configurations may mimic de Sitter like inflation scenaria and
different anisotropic modifications without satisfying any classical
false-vacuum equation of state. Finally, we speculate on perspectives when such
off-diagonal solutions can be related to dark energy and dark matter problems
in modern cosmology.Comment: latex2e, 11pt, 33 pages with table of content, a variant accepted to
IJT