631 research outputs found
Conformal Collineations and Ricci Inheritance Symmetry in String Cloud and String Fluids
Conformal collineations (a generalization of conformal motion) and Ricci
inheritance collineations, defined by , for
string cloud and string fluids in general relativity are studied. By
investigating the kinematical and dynamical properties of such fluids and using
the field equations, some recent studies on the restrictions imposed by
conformal collineations are extended, and new results are found.Comment: 12 pages, LaTeX, no figures, to appear in Int. J. Mod. Phys.
A General Relativistic Model for the Gravitational Field of Active Galactic Nuclei Surrounded by a Disk
An exact but simple general relativistic model for the gravitational field of
active galactic nuclei is constructed, based on the superposition in Weyl
coordinates of a black hole, a Chazy-Curzon disk and two rods, which represent
matter jets. The influence of the rods on the matter properties of the disk and
on its stability is examined. We find that in general they contribute to
destabilize the disk. Also the oscillation frequencies for perturbed circular
geodesics on the disk are computed, and some geodesic orbits for the superposed
metric are numerically calculated.Comment: 24 pages, LATEX. Phys. Rev. D (in press
On Multipolar Analytical Potentials for Galaxies
We present analytical potential-density pairs in three dimensions for the
gravitational field of galaxies, obtained by thickening the multipolar
expansion up to the quadrupole term. These may be interpreted as
generalizations of the Miyamoto and Nagai potential-density pairs. With a
suitable restriction on the possible values of the multipole moments, the
density distributions are positive and monotone decreasing functions of the
radial and axial coordinates
Quantum Singularities in Static Spacetimes
We review the mathematical framework necessary to understand the physical
content of quantum singularities in static spacetimes. We present many examples
of classical singular spacetimes and study their singularities by using wave
packets satisfying Klein-Gordon and Dirac equations. We show that in many cases
the classical singularities are excluded when tested by quantum particles but
unfortunately there are other cases where the singularities remain from the
quantum mechanical point of view. When it is possible we also find, for
spacetimes where quantum mechanics does not exclude the singularities, the
boundary conditions necessary to turn the spatial portion of the wave operator
into self-adjoint and emphasize their importance to the interpretation of
quantum singularities.Comment: 14 pages, section Quantum Singularities has been improve
Chaos in Periodically Perturbed Monopole + Quadrupole Like Potentials
The motion of a particle that suffers the influence of simple inner (outer)
periodic perturbations when it evolves around a center of attraction modeled by
an inverse square law plus a quadrupole-like term is studied. The equations of
motion are used to reduce the Melnikov method to the study of simple graphics.Comment: 12 pages, 6 Postscript figure
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