Showing papers on "Gravitation published in 1987"
TL;DR: In this paper, a two dimensional induced quantum gravity is analyzed using light-cone gauge and the Wess-Zumino action and its connection with SL (2, ℝ) current algebra.
Abstract: Two dimensional induced quantum gravity is analyzed. By the use of light-cone gauge we derive a gravitational analogue of the Wess-Zumino action and discover its amazing connection with SL (2, ℝ) current algebra. The latter permits us to find differential equations for the correlation functions.
673 citations
TL;DR: In this article, it was shown that the gravitational interaction of massless higher-spin fields (s > 2) does exist at least in the first nontrivial order, despite a widespread belief.
574 citations
TL;DR: In this article, a dynamical process is described in which the cosmological constant is netralized through the quantum creation of closed membranes by totally antisymmetric tensor and gravitational fields.
329 citations
TL;DR: In this article, the authors investigated the possibility that spacetime is a membrane embedded in higher dimensions and presented cosmological solutions of d-dimensional Einstein-Maxwell theory which compactify to two dimensions.
324 citations
TL;DR: A semianalytic technique is employed, based on a modified WKB approach, to determine the complex normal-mode frequencies of Schwarzschild black holes, and the WKB estimates agree with numerical results to better than 0.5%.
Abstract: We employ a semianalytic technique, based on a modified WKB approach, to determine the complex normal-mode frequencies of Schwarzschild black holes. It yields a simple analytic formula that gives the real and imaginary parts of the frequency in terms of the parameters of the black hole and of the field whose perturbation is under study, and in terms of the quantity (n+(1/2)), where n=0,\ifmmode\pm\else\textpm\fi{}1,\ifmmode\pm\else\textpm\fi{}2,..., and labels the fundamental mode, first overtone mode, and so on. In the case of the fundamental gravitational normal modes of the Schwarzschild black hole, the WKB estimates agree with numerical results to better than 0.13% in the real part of the frequency and 0.22% in the imaginary part. The agreement for both the real and imaginary parts of the low overtones is better than 0.5%. The relative agreement improves with increasing angular harmonic.
271 citations
TL;DR: In this article, it was shown that pure quantum states will appear to decay into mixed states in any theory of quantum gravity that allows the topology of spacetime to be non simply connected.
234 citations
TL;DR: In this article, the cosmon is assumed to be the Goldstone boson of dilatation and to be broken spontaneously near the Planck scale, which drives the cosmological constant to zero, provided that the energy-momentum trace is purely anomalous.
228 citations
TL;DR: In this paper, the Hamiltonian for the second-order field equations in d spacetime dimensions is constructed, and the contribution of each dimension is given by the continuation of the Euler characteristic of a lower dimension.
Abstract: The most general gravitational action that yields second-order field equations in d spacetime dimensions is a sum of contributions associated with all even dimensions below d. Each contribution is given by the continuation to dimension d of the Euler characteristic of a lower dimension. The Hamiltonian for that general theory is constructed. At high curvatures it is multiple valued.
196 citations
TL;DR: In this article, the variational theory of an ideal spinning fluid is developed, which is described by original Weyssenhoff-Raabe tensors of spin and energy-momentum.
Abstract: The variational theory of an ideal spinning fluid is developed. This is described by original Weyssenhoff-Raabe tensors of spin and energy-momentum. Both neutral and charged fluids are considered, and the equations of motion and conservation laws for the Weyssenhoff neutral fluid in the Riemann-Cartan spacetime are discussed. The results are applied to the study of cosmological models with rotation, shear and expansion in the framework of the Einstein-Cartan theory of gravity.
174 citations
TL;DR: A recent reexamination of experiments performed early in the century on the equivalence of inertial and gravitational mass may have provided either observational clues to the unification of gravity with electroweak and strong nuclear forces or an indication of a new, previously unrecognized force as mentioned in this paper.
Abstract: Geophysical measurements of the gravitational constant and a recent reexamination of experiments performed early in the century on the equivalence of inertial and gravitational mass may have provided either observational clues to the unification of gravity with electroweak and strong nuclear forces or an indication of a new, previously unrecognized force. The evidence is still less than completely conclusive but it has now become difficult to find explanations of the geophysical observations other than non-Newtonian gravity. We also point to the requirements of the next generation of experiments. These include measurements of gravity or gravity gradient in the deep ocean and high above it and Von Eoetvoes-type experiments in steep terrain to test the possibility that a postulated short-range (100 to 1000 m) component of gravity depends upon fundamental particle count rather than mass.
TL;DR: Using the path-ordered products of the relevant affine connection, the effect of the parallel transport of vectors and spinors around closed paths in the field corresponding to the cylindrically symmetric cosmic string is examined.
Abstract: Using the path-ordered products of the relevant affine connection we examine the effect of the parallel transport of vectors and spinors (three-dimensional case only) around closed paths (circles) in the field corresponding to the cylindrically symmetric cosmic string. We compute the solution for three-dimensional gravity also.
Journal Article•
TL;DR: In this paper, the FitzGerald contraction is used to test the new law of gravitation and the old law of gravity, and other tests of the theory of gravity are presented.
Abstract: Eclipse instruments at Sobral Foreword Preface What is geometry? 1. The FitzGerald contraction 2. Relativity 3. The world of four dimensions 4. Fields of force 5. Kinds of space 6. The new law of gravitation and the old law 7. Weighing light 8. Other tests of the theory 9. Momentum and energy 10. Towards infinity 11. Electricity and gravitation 12. On the nature of things Mathematical notes Historical note.
TL;DR: In this article, it was concluded that there are no significant constraints on possible spatial variations in Newton's constant at large distances, and the implications of a simple force law correction to Newtonian gravity from planetary to cosmological distances are discussed.
Abstract: Experimental or observational tests of the 1/r-squared gravitational force law are weak or nonexistent at length scales beyond the solar system. This is because at long distances all astrophysical estimates of mass density based on dynamics give larger values than corresponding measurements based on observed luminosity and local mass-to-luminosity ratios. The discrepancy generally increases with increasing distance, from galactic lengths to at least cluster scales near 10 Mpc, and is usually interpreted as evidence for missing mass. From an empirical perspective that does not recognize the existence of dark matter unless it is nondynamically confirmed, it could be concluded that there are no significant constraints on possible spatial variations in Newton's constant at large distances. The implications of a simple force law correction to Newtonian gravity from planetary to cosmological distances are discussed. 37 references.
TL;DR: It is shown how flux quantization, the Meissner effect, and properties of liquid helium can be utilized to meet the challenges of precision tests of gravity laws and for applications in gravity survey and inertial navigation.
Abstract: Because of the equivalence principle, a global measurement is necessary to distinguish gravity from acceleration of the reference frame. A gravity gradiometer is therefore an essential instrument needed for precision tests of gravity laws and for applications in gravity survey and inertial navigation. Superconductivity and SQUID (superconducting quantum interference device) technology can be used to obtain a gravity gradiometer with very high sensitivity and stability. A superconducting gravity gradiometer has been developed for a null test of the gravitational inverse-square law and space-borne geodesy. Here we present a complete theoretical model of this instrument. Starting from dynamical equations for the device, we derive transfer functions, a common mode rejection characteristic, and an error model of the superconducting instrument. Since a gradiometer must detect a very weak differential gravity signal in the midst of large platform accelerations and other environmental disturbances, the scale factor and common mode rejection stability of the instrument are extremely important in addition to its immunity to temperature and electromagnetic fluctuations. We show how flux quantization, the Meissner effect, and properties of liquid helium can be utilized to meet these challenges.
TL;DR: In this article, a Born-Oppenheimer type approximation of the SCAG solution of the Wheeler-De Witt equation has been proposed, which allows for the feedback of matter onto gravity, wherein the latter is driven by the (quantum) mean energy-momentum tensor of matter.
Abstract: Time arises in the theory of gravity through the semiclassical approximation of the gravitational part of the solution of the Wheeler-De Witt equation in the manner shown by Banks (SCAG). We generalize Banks' procedure by grafting a Born-Oppenheimer type approximation onto SCAG. This allows for the feedback of matter onto gravity, wherein the latter is driven by the (quantum) mean energy-momentum tensor of matter. The wave function is nonvanishing in classically forbidden configurations of gravity. In SCAG this is described by the evolution of matter in imaginary time. This is interpreted as an inverse temperature, and the norm of the matter wave function, no longer conserved for these gravitational configurations, is a partition function. A simple cosmological model is worked out to illustrate these ideas. In this model it is shown that the temperature of the matter which emerges into the classically permitted region is the inverse bounce time of the bounce executed by the system in the forbidden region (behind the horizon).
TL;DR: The full coupled gravity-string field equations are considered and they are used to show that a general local string will have an asymptotically conical structure.
Abstract: The full coupled gravity-string field equations are considered and they are used to show that a general local string will have an asymptotically conical structure For the case of the Abelian Higgs model with U(1) gauge invariance, the gravitational field of a simple local string to first order in Geta/sup 2/ is exhibited Then a C-energy argument is used to suggest stability at this linearized level
TL;DR: In this paper, it was shown that the Yang-Mills fields equations are equivalent to integrability conditions and that the latter can also be interpreted, using local sections, as conservation equations of the local pseudo-densities of energy-momentum and Yang-mills charge respectively.
Abstract: We show that expressed in the appropriate principal bundles, the gravitational and Yang-Mills fields equations are equivalent to integrability conditions and that the latter can also be interpreted, using local sections, as conservation equations of the local pseudo-densities of energy-momentum and Yang-Mills charge respectively. These densities can be related using a Kaluza-Klein unification.
TL;DR: In this paper, the authors investigated the stability of the de Sitter solution in the presence of bulk viscous stresses which violate the strong energy condition but obey the weak and dominant energy conditions.
TL;DR: In an effort that has spanned more than a century to connect gravitation to the other forces of nature, over 200 experiments on G have been completed and reported; but many of them have not been reported in what would now be considered to be the open literature as mentioned in this paper.
Abstract: The Newtonian Gravitational Constant, G, has probably been measured more often but, interestingly, with less precision than any other physical constant of fundamental importance. In an effort that has spanned more than a century to connect gravitation to the other forces of nature, over 200 experiments on G have been completed and reported; but many of them have not been reported in what would now be considered to be the open literature. This paper is a third, more complete attempt to carry MacKenzie's and Poynting's bibliographies forward from the 1800's to the present; and thereby include as many as possible of the experimental results on G that have been obtained since 1900.
TL;DR: The field equations for Barber's two self-creation theories of gravitation were solved for Friedmann-Robertson-Walker space times, using perfect fluid energy-momentum tensors as mentioned in this paper.
Abstract: The field equations for Barber's two self-creation theories of gravitation are solved for Friedmann-Robertson-Walker space times, using perfect fluid energy-momentum tensors. Barber's first theory is discussed for the radiation dominated case, whereas cosmologies according to Barber's second sefl-creation theory are constructed for vacuum-dominated, radiation-dominated, and dust-filled cases.
01 Jan 1987
TL;DR: In an effort that has spanned more than a century to connect gravitation to the other forces of nature, over 200 experiments on G have been completed and reported; but many of them have not been reported in what would now be considered to be the open literature.
Abstract: The Newtonian Gravitational Constant, G, has probably been measured more often but, interestingly, with less precision than any other physical constant of fundamental importance. In an effort that has spanned more than a century to connect gravitation to the other forces of nature, over 200 experiments on G have been completed and reported; but many of them have not been reported in what would now be considered to be the open literature. This paper is a third, more complete attempt to carry MacKenzie's and Poynting's bibliographies forward from the 1800's to the present; and thereby include as many as possible of the experimental results on G that have been obtained since 1900.
TL;DR: In this article, the authors reviewed the classical concept of hydrodynamic stability in the light of recent developments in semigeostrophic theory and showed that a certain Jacobian matrix is required to be positive-definite if the solution of the semi-geophysical equations is to be well posed.
Abstract: The classical concept of hydrodynamic stability is reviewed in the light of recent developments in semigeostrophic theory. A certain Jacobian matrix is required to be positive-definite if solution of the semigeostrophic equations is to be well posed. formally, this gives three conditions which must be satisfied, one of which corresponds to the positivity of the semigeostrophic potential vorticity defined as the determinant of the matrix. The full implications of these stability criteria are sought here, together with some simple expression of the positive-definite requirement. The existence of a minimum energy principle, with respect to virtual parcel displacements which conserve absolute momentum and potential temperature is shown to play a key role, as in the equivalent circular vortex problem studied by Fjortoft. It also appears to provide the basis for extending semigeostrophic theory to the general geophysical situation in which the gravitation vector and axis of rotation are not colinear.
01 Aug 1987
TL;DR: In this paper, idealized homogeneous systems - basic ideas and gentle relaxation have been proposed for galaxy clustering, including inhomogeneous systems, spherical systems, and flattered systems.
Abstract: Preface Introduction 1. Idealized homogeneous systems - basic ideas and gentle relaxation 2. Infnite inhomogeneous systems - galaxy clustering 3. Finite spherical systems - cluster of galaxies, galactic nuclei, globular clusters 4. Finite flattered systems - galaxies Index.
TL;DR: In this article, the inverse scattering method is used to obtain a class of solutions of the vacuum Einstein equations describing the space-time following the collision of two gravitational plane waves, and the general features of these solutions are analyzed in terms of the behavior of the Weyl scalars, and some degenerate cases are discussed.
Abstract: The inverse scattering method is used to obtain a class of solutions of the vacuum Einstein equations describing the space-time following the collision of two gravitational plane waves. The general features of these solutions are analyzed in terms of the behavior of the Weyl scalars, and some degenerate cases are discussed.
TL;DR: The Lagrange method was used to obtain a class of solutions of the three-dimensional hydrodynamical equations governing the motion of matter with vanishing pressure in its own Newtonian gravitational field.
Abstract: The Lagrange method is used to obtain a class of solutions of the three‐dimensional hydrodynamical equations governing the motion of matter with vanishing pressure in its own Newtonian gravitational field. The class is characterized by the property that each fluid particle has constant acceleration. The class contains rotational and irrotational flows. For rotational flows the expansion tensor has one zero eigenvalue, while for irrotational flows it has two zero eigenvalues, which implies that every fluid element contracts or expands in two or one spatial directions, respectively; nevertheless, the density depends on all three coordinates. The general one‐dimensional solution is included as a subclass.