Hasil untuk "gr-qc"

T. Yetkin, A. Havare

S. Hayward

This is a comment on a reply (gr-qc/9601040) to a comment (gr-qc/9606045) on a paper of Hellaby & Dray (gr-qc/9404001), repeating the identification of an important mistake which is still being denied by the authors: their proposed solutions do not satisfy the Einstein- Klein-Gordon equations at a change of signature. Substitution of the proposed solutions into the Einstein-Klein-Gordon equations in unit normal coordinates yields Dirac delta terms describing source layers at the junction. Hellaby & Dray's criticisms of this straightforward calculation are absurd: it does not involve "imaginary time", it does not involve a "modified form" of the field equations, and it is "purely classical". Moreover, Hellaby & Dray's latest attempt to lose the delta terms is mathematically invalid, involving division by zero and products of distributions, hinging on an identity whose incorrectness may be checked by substitution.

S. Gharanfoli, A. Abbassi

1- It is shown that the upper bound for $\alpha$ in the general solutions of spherically symmetric vacuum field equations(gr-qc/9812081,$\Lambda$=0) is nearly 10^3.This has been obtained by comparing the theoretical prediction for bending of light and precession of perihelia with observation. For a significant range of possible values of$\alpha$ ($\alpha$ >2) the metric is free of coordinate singularity. 2- It is checked that the singularity in the non-static spherically symmetric solution of Einstein field equations with $\Lambda$ (JHEP04(1999)011,$\alpha$ = 0)at the origin is intrinsic. 3- Using the techniques of these two works, ageneral class of non-static solutions is presented. They are smooth and finite everywhere and have an extension larger than Schwarzschild metric. 4- The geodesic equations of a freely material particle for the general case are solved which reveals a Schwarzschild -deSitter type potential field.

M. Salti, O. Aydoğdu, A. Havare et al.

This paper has been removed by arXiv administrators because it plagiarizes P.K. Jena, P.C. Naik and T. Pradhan, "Photon As The Zero Mass Limit Of Dkp Field," J. Phys. A {\bf 13}, 2975 (1980) [not cited within submission]. In addition, the following submissions by the authors and their collaborators all contain a great deal of overlap: gr-qc/0502059, gr-qc/0502061, gr-qc/0207026, hep-th/0110228, and hep-th/0207088.

G.Sardanashvily

In Parts I,II of the work (gr-qc/9405013, 9407032), we have shown that gravity is sui generis a Higgs field corresponding to spontaneous symmetry breaking when the fermion matter admits only the Lorentz subgroup of world symmetries of the geometric arena. From the mathematical viewpoint, the Higgs nature of gravity is-sues from the fact that different gravitational fields are responsible for nonequivalent representations of cotangent vectors to a world manifold by γ -matrices on spinor bundles. It follows that gravitational fields fail to form an affine space modelled on a linear space of deviations of some background field. In other words, even weak gravitational fields do not satisfy the superposition principle and, in particular, can not be quantized by usual methods. At the same time, one can examine superposable deviations σ of a gravitational field h so that h + σ fail to be a gravitational field. These deviations get the adequate mathematical description in the framework of the affine group gauge theory in dislocated manifolds, and their Lagrangian densities differ from the familiar gravitational Lagrangian densities. They make contribution to the standard gravitational effects, e.g., modify Newton’s gravitational potential.

G. Sardanashvily

P. Zizzi

A. Anderson

A proof is given that the polar decomposition procedure for unitarity restoration works for products of invertible nonunitary operators. A brief discussion follows that the unitarity restoration procedure, applied to propagators in spacetimes containing closed timelike curves, is analogous to the original introduction by Feynman of ghosts to restore unitarity in non-abelian gauge theories. (The substance of this paper will be a note added in proof to the published version of gr-qc/9405058, to appear in Phys Rev D.)

R. Cárdenas, I. Quirós, R. Bonal

In reference gr-qc/0104036 a four-dimensional effective theory of gravity embeddable in a five-dimensional "distorted" Randall-Sundrum brane scenario was derived. The present paper is aimed at the application of such a theory to describe physics in an open Friedmann-Robertson-Walker (Weyl-symmetric) universe. It is shown that regular bouncing universes arise for a given range of the free parameter of the theory.

M. Zotov

Recently, Byland and Scialom studied the evolution of the Bianchi I, the Bianchi III and the Kantowski-Sachs universe on the basis of dynamical systems methods (Phys. Rev. D57, 6065 (1998), gr-qc/9802043). In particular, they have pointed out a problem to determine the stability properties of one of the degenerate critical points of the corresponding dynamical system. Here we give a solution, showing that this point is unstable both to the past and to the future. We also discuss the asymptotic behavior of the trajectories in the vicinity of another critical point.

L. Finn

This paper has been withdrawn due to a crucial error in combining the two probability sectors represented in equations 13 and 14. Corrected, one can recover, in the limit of no background, the results of Allen et al. The general result that an analysis allowing for a background permits a substantial improvement of the limit still holds, though the presentation in the gr-qc/9907070 is flawed.

E.A.Tagirov

This paper is the first of two papers devoted to formulation of quantum mechanics of a particle in a normal geodesic frame of reference in the general Riemannian space–time. Here canonical quantization of geodesic motion in the 1+3–formalism is considered, the result of which will be compared in the subsequent paper II with that of the field–theoretical approach, see also gr-qc/9807030. The Schr¨odinger representation of quantum-mechanical kinematics and dynamics is presented in the general–covariant form and a physical interpretation of the state vectors and the position operators is discussed.

C. Gundlach

It is pointed out that the entropy of a membrane which is quantized perturbatively around a background position of fixed radius in a black hole spacetime is equal to the Bekenstein-Hawking entropy, if 1) the membrane surface is the horizon surface plus one Planck unit, and 2) its temperature is the Hawking temperature. (This is a comment on gr-qc 9411037.)

J. Guven, N. Murchadha

We continue our examination of the constraints in spherically symmetric general relativity begun in I (gr-qc/9411009) and II (gr-qc/9411010). We extend to general configurations with $J\ne 0$ the analysis of II which treated a moment of time symmetry. We exploit the one parameter family of foliations introduced in I which are linear and homogeneous in the extrinsic curvature to characterize apparent horizons and spatial singularities in the initial data. In particular, we demonstrate that these characterizations do not depend sensitively on the foliation.

M. Salti, O. Aydoğdu

This paper has excessive overlap with the following paper also written by the authors or their collaborators: gr-qc/0511095.

S. Deser

The above hep-th posting purports -- erroneously -- to be a comment on a Note by me in gr-qc.

D. Brill

This is the reply given at the conference ``Mach's Principle" at T\"ubingen in July 1993 to the paper by Isenberg (1993a). Unfortunately the Isenberg paper itself was not submitted to gr-qc.

F. Binbay, I. Acikgoz, M. Salti

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/9803014, "A White Hole Model of the Big Bang," by Philip Gibbs.

D. Brill

This is a reply, given at the conference ``Mach's Principle" in T\"ubingen in July 1993, to the paper by Pfister (1993). Unfortunately the Pfister paper itself was not sent to gr-qc.

F. Henry-Couannier

The previous version of this article gave erroneous predictions. The correct uptodate predictions can be found in the section devoted to gravitomagnetism in the living review of the Dark Gravity theory: gr-qc/0610079 The most natural prediction is zero frame dragging and the same geodetic effect as predicted by GR. However, a straightforward extension of the theory could lead to the same frame-dragging as in GR.