35 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.
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
On the derivation of the spacetime metric from linear electrodynamics
In the framework of metric-free electrodynamics, we start with a {\em linear}
spacetime relation between the excitation 2-form and
the field strength 2-form . This linear relation is constrained by
the so-called closure relation. We solve this system algebraically and extend a
previous analysis such as to include also singular solutions. Using the
recently derived fourth order {\em Fresnel} equation describing the propagation
of electromagnetic waves in a general {\em linear} medium, we find that for all
solutions the fourth order surface reduces to a light cone. Therefrom we derive
the corresponding metric up to a conformal factor.Comment: 11 Pages, LaTeX, some typos corrected, one reference added. Version
published in Physics Letters
Relativistic analysis of the dielectric Einstein box: Abraham, Minkowski and total energy-momentum tensors
We analyse the "Einstein box" thought experiment and the definition of the
momentum of light inside matter. We stress the importance of the total
energy-momentum tensor of the closed system (electromagnetic field plus
material medium) and derive in detail the relativistic expressions for the
Abraham and Minkowski momenta, together with the corresponding balance
equations for an isotropic and homogeneous medium. We identify some assumptions
hidden in the Einstein box argument, which make it weaker than it is usually
recognized. In particular, we show that the Abraham momentum is not uniquely
selected as the momentum of light in this case