Showing papers on "Gravitation published in 1990"
1,486 citations
TL;DR: A nonperturbative definition of two-dimensional quantum gravity is proposed, based on a double-scaling limit of the random-matrix model, and an exact differential equation for the partition function ofTwo-dimensional gravity coupled to conformal matter is derived.
Abstract: We propose a nonperturbative definition of two-dimensional quantum gravity, based on a double-scaling limit of the random-matrix model. We derive an exact differential equation for the partition function of two-dimensional gravity coupled to conformal matter as a function of the string coupling constant that governs the genus expansion of two-dimensional surfaces, and discuss its properties and consequences. We also construct and discuss the correlation functions of an infinite set of local operators for spherical topology.
945 citations
TL;DR: In this paper, the authors determine all solutions to the consistency equations which have to be satisfied by anomalies in gravitational theories with a Poincare-invariant ground state, i.e.
542 citations
TL;DR: In this paper, a nonperturbative definition of two-dimensional quantum gravity, based on a double scaling limit of the random matrix model, was proposed, and an operator formalism for utilizing the method of orthogonal polynomials that allows us to solve the matrix models to all orders in the genus expansion was developed.
401 citations
367 citations
TL;DR: In this article, the authors derived the subleading terms of an eikonal function up to two loops and for D = 4, they found a finite and positive classical correction to the Einstein deflection, implying a deviation from the external metric picture.
342 citations
TL;DR: The dynamical evolution of the perturbed ground-state boson stars in numerical relativity is reported on, with implications on the actual existence and the formation of bosonStars in an astrophysical environment.
Abstract: This is the first paper in a series in which we study the dynamical evolution of self-gravitating complex scalar field configurations (boson stars) in numerical relativity. Boson stars have equilibrium configurations corresponding to different levels of excitation of the scalar fields (i.e., different numbers of nodes). In this paper we report on the dynamical evolution of the perturbed ground-state boson stars. The major results are the following. (i) Under finite perturbations (with possibly finite changes in the total mass $M$ and the particle number $N$), the ground-state configurations of a boson star consist of a stable branch and an unstable branch. The transition point corresponds to a critical mass of $M=0.633(\frac{{M}_{\mathrm{Planck}}^{2}}{m})$, where $m$ is the mass of the scalar field, depending slightly on the type of perturbation considered. This extends the previous result obtained by other authors that there are two such branches under infinitesimal perturbations with fixed $M$ and $N$. (ii) The configurations on the stable branch, when perturbed, will oscillate, emit scalar field radiation with a characteristic frequency, and settle down into a new configuration with less mass and a larger radius than the initial perturbed configuration. The quasinormal frequency and the decay rate have been studied. The decay rate is an increasing function of the oscillation amplitude. (iii) The configurations on the unstable branch, when perturbed, either collapse to a black hole or migrate to and eventually settle down on the stable branch, depending on the type of perturbation. This behavior has been seen in initial configurations with both positive and negative binding energies. These results have implications on the actual existence and the formation of boson stars in an astrophysical environment.
252 citations
TL;DR: In this paper, a modification of Di\`osi's model is proposed, which overcomes the difficulties and retains partially its appealing features, allowing the derivation from microdynamics of wave-packet reduction, and accounts for the emergence of definite macroscopic properties for macroobjects.
Abstract: A continuous-reduction model implying the dynamical suppression of linear superpositions of macroscopically distinguishable states, presented recently by Di\`osi [Phys. Rev. A 40, 1165 (1989)], is investigated. The model exhibits appealing features; in particular, it relates reduction to gravity and contains no constants besides Newton's gravitational constant G. It turns out, however, that the model is not fully consistent. A slight modification of this model is proposed, which overcomes the difficulties and retains partially its appealing features. The resulting model deals with systems containing distinguishable or identical constituents, allows the derivation from microdynamics of wave-packet reduction, and accounts for the emergence of definite macroscopic properties for macro-objects. Reduction is related to gravity in the same way as in Di\`osi's model, but a fundamental length must be introduced to avoid inconsistencies.
245 citations
TL;DR: In this article, the correlation functions of operators in these models can also be easily computed and it is shown that two kinds of operators, microscopic and macroscopic loops, contain all the information about integrals over the surface of local operators.
243 citations
TL;DR: This work presents a systematic study of cosmological solutions in the Lovelock theory of gravitation, including maximally symmetric space-times, Robertson-Walker universes, and product manifolds of symmetric subspaces.
Abstract: We present a systematic study of cosmological solutions in the Lovelock theory of gravitation, including maximally symmetric space-times, Robertson-Walker universes, and product manifolds of symmetric subspaces.
233 citations
TL;DR: In this paper, the authors studied the nonperturbative effects of the quantum fluctuation of gravity by means of the ϵ-expansion around two dimensions and the renormalization group method.
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TL;DR: In this paper, a nonperturbative two-dimensional quantum gravity coupled to a single bosonic field (d = 1 matter) is considered, where the scaling parameter α∝1n(g-gc)N is fixed.
TL;DR: In this paper, the authors investigate the physics of black hole 1 + 1 dimensions and demonstrate how an event horizon structure can arise in two dimensions given a variety of energymomentum tensors, cataloguing the resultant particular solutions.
TL;DR: The quantization of spherically symmetric gravitational systems using the Dirac formalism and the WKB approximation is developed for the nucleation of false-vacuum bubbles, which may have been the origin of the inflationary universe and matter.
Abstract: We develop the quantization of spherically symmetric gravitational systems using the Dirac formalism and the WKB approximation. The particular application is the nucleation of false-vacuum bubbles, which may have been the origin of the inflationary universe and matter. Consistency between our results and those obtained by the Euclidean method requires that the latter include metrics with degeneracies. Our work also raises several other questions of principle, including the meaning of the wave function and the necessity of topology change. A tentative application of this work to quantum cosmology indicates that the "Hartle-Hawking wave function" is inconsistent.
TL;DR: This work solves numerically the coupled equations for the metric and the scalar field, to precisely determine this repulsive gravitational potential and in order to analyze the solution when gravitational effects are already significant close to the monopole core.
Abstract: A monopole formed as a consequence of the spontaneous breakdown of a global symmetry should have a mass that grows linearly with the distance off its core. It was recently shown by Barriola and Vilenkin that the gravitational effect of this configuration is equivalent to that of a deficit solid angle in the metric, plus that of a relatively tiny mass at the origin. Here we show that this small effective mass is negative. Global monopoles thus share with other topological defects, such as domain walls and global strings, a repulsive gravitational potential. We solve numerically the coupled equations for the metric and the scalar field, to precisely determine this repulsive potential and in order to analyze the solution when gravitational effects are already significant close to the monopole core. We study the motion of test particles in a monopole background, and discuss the possible implications of a negative effective mass.
TL;DR: In this article, the interaction of point particles in a gauge theory for gravity in 2 + 1 dimensions with particular emphasis on the effects of spin is analyzed, and it is shown that the known space-time solution for spinning sources in Einstein gravity exhibits torsion at the location of the sources.
TL;DR: In this article, the difficulties of conservation laws in general relativity are discussed, with special reference to the non-tangible nature of gravitational energy and its transformation into tangible forms of energy.
Abstract: The difficulties of conservation laws in general relativity are discussed, with special reference to the non-tangible nature of gravitational energy and its transformation into tangible forms of energy. Inductive transfer of energy is marked out as wholly distinct from wave transfer. Slow (adiabatic) changes are utilized to make clear, in the axi-symmetric case, that the mass of an isolated body is conserved irrespective of any local changes (e.g. of shape) and that in inductive transfer the movement of energy between two bodies can readily be traced by the changes in their masses.
01 Oct 1990
TL;DR: Corrections to the Schr\"odinger equation which arise from the quantization of the gravitational field are derived through an expansion of the full functional Wheeler-DeWitt equation with respect to powers of the Gravitational constant.
TL;DR: In this article, the authors studied the flow of the m = 3 multicritical matrix theory and the pure quantum gravity theory, and they found behavior in the flow indicative of a nonperturbative instability.
TL;DR: In this paper, a simple way of deriving cosmological perturbation equations in generalised gravity theories which accounts for metric perturbations in a gauge-invariant way is presented.
Abstract: The author presents a simple way of deriving cosmological perturbation equations in generalised gravity theories which accounts for metric perturbations in a gauge-invariant way. The author uses an imperfect fluid formulation of the perturbation equations developed in Einstein gravity and absorb all new contributions as effective fluid quantities. The author applies this approach to the f( phi , R)- omega ( phi ) phi ,c phi c Lagrangian which includes most of the gravity theories employing a scalar field and scalar curvature. The relation between the proposed method and the conformal transformation method is discussed. Background and perturbation equations are displayed for specific gravity theories which can be recovered as special cases from the above general Lagrangian.
TL;DR: Gravitational radiation from an infinite string with a helicoidal standing wave with radiation power and spectrum is studied in the weak-field approximation for gravitational damping of small-scale structure on the long strings.
Abstract: Gravitational radiation from an infinite string with a helicoidal standing wave is studied in the weak-field approximation. The radiation power and the spectrum are calculated. The implications of the results for gravitational damping of small-scale structure on the long strings are briefly discussed.
TL;DR: The 4D self-dual gravity is shown to be equivalent to a large-N limit of the 2D non-linear sigma model with Wess-Zumino terms only as discussed by the authors.
TL;DR: In this article, the mass of the innermost stable circular orbits around weakly magnetized neutron stars is determined by detecting X-ray emission from clumps of matter before and after they cross the gap between the inner accretion disk and the stellar surface.
Abstract: If neutron stars have radii as small as has been argued by some, observations of accretion-powered X-rays could verify the existence of innermost stable circular orbits (predicted by general relativity) around weakly magnetized neutron stars. This may be done by detecting X-ray emission from clumps of matter before and after they cross the gap (where matter cannot be supported by rotation) between the inner accretion disk and the stellar surface. Assuming the validity of general relativity, it would then be possible to determine the masses of such neutron stars independently of any knowledge of binary orbital parameters. If an accurate mass determination were already available through any of the methods conventionally used, the new mass determination method proposed here could then be used to quantitatively test strong field effects of gravitational theory.
01 Jan 1990
TL;DR: In this paper, the Fermat principle is used to derive the zigzag path constructed for massive and massless particles in order to determine if these paths are a suitable approximation to the first order of the gravitational lens effect.
Abstract: The Fermat principle is reviewed and used to derive the zigzag path constructed for massive and massless particles in order to determine if these paths are a suitable approximation to the first order of the gravitational lens effect It is found that such paths are suitable for thin comoving gravitational lenses to the first order in the lens effect, and also if there is a nonstationary perturbation As an example, the Fermat principle is applied to a perturbation by gravitational waves, and the transverse velocity of the caustic motion is derived This velocity creates difficulty for the proposal by McBreen and Metcalfe (1988) that gamma-ray bursts come from small, hot BL Lac cores crossed by microcaustics 23 refs
TL;DR: In this article, a two-dimensional theory of gravity with dynamical metric and torsion is considered, and the equations of motion are reduced to a system of equations for two scalar fields which in particular case yields the Liouville equation.
TL;DR: In this article, a path integral representation of partition functions for various ensembles including that appropriate to the microcanonical ensemble was obtained using the definition of variables conjugate both in the sense of the field theory of general relativity and in thermodynamics, the boundary data of which can be prescribed geometrically using gravity.
Abstract: By including gravitation as described by general relativity as a part of a thermodynamic system, the authors have obtained formal path integral representations of partition functions for various ensembles including that appropriate to the microcanonical ensemble. This is possible because the boundary conditions for certain well posed Euclidean problems in general relativity exactly correspond to boundary conditions of certain well posed problems in thermodynamics. The different ensembles are obtained using the definition of variables conjugate both in the sense of the field theory of general relativity and in the sense of thermodynamics, the boundary data of which can be prescribed geometrically using gravity.
TL;DR: In this article, a topological action for 1 + 1 dimensional gravity based on the gauge symmetry SO(1,2) or its contraction ISO (1,1) is proposed. But it is not shown how to construct a scalar multiplet.
TL;DR: The path integral on a torus in continuum Liouville theory coupled to conformal matter with c\ensuremath{\le}1.1% is calculated, finding agreement with the results obtained in matrix models, topological gravity, and Korteweg de Vries hierarchies.
Abstract: We calculate the path integral on a torus in continuum Liouville theory coupled to conformal matter with c\ensuremath{\le}1. We find agreement with the results obtained in matrix models, topological gravity, and Korteweg\char21{}de Vries hierarchies.