364 research outputs found
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
Geodesics around Weyl-Bach's Ring Solution
We explore some of the gravitational features of a uniform ring both in the
Newtonian potential theory and in General Relativity. We use a spacetime
associated to a Weyl static solution of the vacuum Einstein's equations with
ring like singularity. The Newtonian motion for a test particle in the
gravitational field of the ring is studied and compared with the corresponding
geodesic motion in the given spacetime. We have found a relativistic peculiar
attraction: free falling particle geodesics are lead to the inner rim but never
hit the ring.Comment: 8 figures, 14 pages. LaTeX w/ subfigure, graphic
On the gravitational field of static and stationary axial symmetric bodies with multi-polar structure
We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo
solution of the Einstein Equations in terms of bars. We find that each
multi-pole correspond to the Newtonian potential of a bar with linear density
proportional to a Legendre Polynomial. We use this fact to find an integral
representation of the function. These integral representations are
used in the context of the inverse scattering method to find solutions
associated to one or more rotating bodies each one with their own multi-polar
structure.Comment: To be published in Classical and Quantum Gravit
Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons
The stability of cosmological event and Cauchy horizons of spacetimes
associated with plane symmetric domain walls are studied. It is found that both
horizons are not stable against perturbations of null fluids and massless
scalar fields; they are turned into curvature singularities. These
singularities are light-like and strong in the sense that both the tidal forces
and distortions acting on test particles become unbounded when theses
singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques
Stochastic contribution to the growth factor in the LCDM model
We study the effect of noise on the evolution of the growth factor of density
perturbations in the context of the LCDM model. Stochasticity is introduced as
a Wiener process amplified by an intensity parameter alpha. By comparing the
evolution of deterministic and stochastic cases for different values of alpha
we estimate the intensity level necessary to make noise relevant for
cosmological tests based on large-scale structure data. Our results indicate
that the presence of random forces underlying the fluid description can lead to
significant deviations from the nonstochastic solution at late times for
alpha>0.001.Comment: 6 pages, 1 figur
Circular Orbits in Einstein-Gauss-Bonnet Gravity
The stability under radial and vertical perturbations of circular orbits
associated to particles orbiting a spherically symmetric center of attraction
is study in the context of the n-dimensional: Newtonian theory of gravitation,
Einstein's general relativity, and Einstein-Gauss-Bonnet theory of gravitation.
The presence of a cosmological constant is also considered. We find that this
constant as well as the Gauss-Bonnet coupling constant are crucial to have
stability for .Comment: 11 pages, 4 figs, RevTex, Phys. Rev. D, in pres
On the Solutions of the Lorentz-Dirac Equation
We discuss the unstable character of the solutions of the Lorentz-Dirac
equation and stress the need of methods like order reduction to derive a
physically acceptable equation of motion. The discussion is illustrated with
the paradigmatic example of the non-relativistic harmonic oscillator with
radiation reaction. We also illustrate removal of the noncasual
pre-acceleration with the introduction of a small correction in the
Lorentz-Dirac equation.Comment: 4 eps figs. to be published in GR
General-relativistic Model of Magnetically Driven Jet
The general scheme for the construction of the general-relativistic model of
the magnetically driven jet is suggested. The method is based on the usage of
the 3+1 MHD formalism. It is shown that the critical points of the flow and the
explicit radial behavior of the physical variables may be derived through the
jet ``profile function."Comment: 12 pages, LaTex, no figure
Superposition of Weyl solutions: The equilibrium forces
Solutions to the Einstein equation that represent the superposition of static
isolated bodies with axially symmetry are presented. The equations nonlinearity
yields singular structures (strut and membranes) to equilibrate the bodies. The
force on the strut like singularities is computed for a variety of situations.
The superposition of a ring and a particle is studied in some detailComment: 31 pages, 7 figures, psbox macro. Submitted to Classical and Quantum
Gravit
Two Kerr black holes with axisymmetric spins: An improved Newtonian model for the head-on collision and gravitational radiation
We present a semi-analytical approach to the interaction of two (originally)
Kerr black holes through a head-on collision process. An expression for the
rate of emission of gravitational radiation is derived from an exact solution
to the Einstein's field equations. The total amount of gravitational radiation
emitted in the process is calculated and compared to current numerical
investigations. We find that the spin-spin interaction increases the emission
of gravitational wave energy up to 0.2% of the total rest mass. We discuss also
the possibility of spin-exchange between the holes.Comment: 8 pages, RevTeX, 2 figures, psbox macro include
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