87 research outputs found
A Comment on Bonnor-Steadman Closed Timelike Curves
The existence and stability closed timelike curves in a Bonnor-Ward spacetime
without torsion line singularities is shown by exhibiting particular examples.Comment: 2 pages, RevTex, minor correction
Continuous media interpretation of supersymmetric Wess-Zumino type models
Supersymmetric Wess-Zumino type models are considered as classical material
media that can be interpreted as fluids of ordered strings with heat flow along
the strings or a mixture of fluids of ordered strings with either a cloud of
particles or a flux of directed radiation.Comment: 14 pages, Latex, No Figure
Local And Global Structure Of A Thick-domain-wall Space-time
The local and global properties of the Goetz thick plane domain-wall space-time are studied. It is found that when the surface energy of the wall is greater than a critical value c, the space-time will be closed by intermediate singularities at a finite proper distance. A model is presented in which these singularities will give rise to scalar ones when interacting with null fluids. The maximum extension of the space-time of the wall whose surface energy is less than c is presented. It is shown that for a certain choice of the free parameter the space-time has a black hole structure but plane symmetry. © 1995 The American Physical Society.5112R6612R661
Chaos and Rotating Black Holes with Halos
The occurrence of chaos for test particles moving around a slowly rotating
black hole with a dipolar halo is studied using Poincar\'e sections. We find a
novel effect, particles with angular momentum opposite to the black hole
rotation have larger chaotic regions in phase space than particles initially
moving in the same direction.Comment: 9 pages, 4 Postscript figures. Phys. Rev. D, in pres
Spinning Strings, Black Holes and Stable Closed Timelike Geodesics
The existence and stability under linear perturbation of closed timelike
curves in the spacetime associated to Schwarzschild black hole pierced by a
spinning string are studied. Due to the superposition of the black hole, we
find that the spinning string spacetime is deformed in such a way to allow the
existence of closed timelike geodesics.Comment: 5 pages, RevTex4, some corrections and new material adde
Nambu Bubbles With Curvature Corrections
A finite-width correction for a two-dimensional membrane described by the Nambu action modified by the addition of the Ricci curvature scalar is studied. The particular case of a spherical bubble is considered in some detail. © 1990 The American Physical Society.4141333133
Chaos and Taub-NUT related spacetimes
The occurrence of chaos for test particles moving in a Taub-NUT spacetime
with a dipolar halo perturbation is studied using Poincar\'e sections. We find
that the NUT parameter (magnetic mass) attenuates the presence of chaos.Comment: 10 pages, 5 Postscript figure
Hausdorff dimension of repellors in low sensitive systems
Methods to estimate the Hausdorff dimension of invariant sets of scattering
systems are presented. Based on the levels' hierarchical structure of the time
delay function, these techniques can be used in systems whose
future-invariant-set codimensions are approximately equal to or greater than
one. The discussion is illustrated by a numerical example of a scatterer built
with four hard spheres located at the vertices of a regular tetrahedron.Comment: 9 pages, 5 figures, accepted in Physics Letters
High-Speed Cylindrical Collapse of Two Perfect Fluids
In this paper, the study of the gravitational collapse of cylindrically
distributed two perfect fluid system has been carried out. It is assumed that
the collapsing speeds of the two fluids are very large. We explore this
condition by using the high-speed approximation scheme. There arise two cases,
i.e., bounded and vanishing of the ratios of the pressures with densities of
two fluids given by . It is shown that the high-speed approximation
scheme breaks down by non-zero pressures when are bounded
below by some positive constants. The failure of the high-speed approximation
scheme at some particular time of the gravitational collapse suggests the
uncertainity on the evolution at and after this time. In the bounded case, the
naked singularity formation seems to be impossible for the cylindrical two
perfect fluids. For the vanishing case, if a linear equation of state is used,
the high-speed collapse does not break down by the effects of the pressures and
consequently a naked singularity forms. This work provides the generalisation
of the results already given by Nakao and Morisawa [1] for the perfect fluid.Comment: 11 pages, 1 figure, accepted for publication in Gen. Rel. Gra
The Interaction Of Outgoing And Ingoing Spherically Symmetric Null Fluids
Using similarity methods, the Einstein field equations coupled to two oppositely directed null fluids for a spherically symmetric space-time are reduced to an autonomous system of three ordinary differential equations. The space of solutions is studied in some detail and solutions are found that represent: (i) the backscattering of an initially outgoing thick null fluid shell in a background gravitational field with a central naked singularity, (ii) the formation of strong space-time singularities by the interaction of thick null fluid shells, (iii) the interaction of a core of null radiation with an incoming shell of null fluid, and (iv) cosmological models of Kantowski-Sachs type with initial and final singularities clothed by apparent horizons. © 1995 American Institute of Physics.3673663367
- …