Showing papers on "Gravitation published in 1995"
Book•
01 Jan 1995
TL;DR: Einstein Geometrodynamics and Inertia: The Initial-Value Problem in Einstein Geometroynamics as mentioned in this paper and the Gravitomagnetic Field and its Measurement.
Abstract: PrefaceChart of Main Topics1A First Tour12Einstein Geometrodynamics133Tests of Einstein Geometrodynamics874Cosmology, Standard Models, and Homogeneous Rotating Models1855The Initial-Value Problem in Einstein Geometrodynamics2696The Gravitomagnetic Field and Its Measurement3157Some Highlights of the Past and a Summary of Geometrodynamics and Inertia384Mathematical Appendix403Symbols and Notations437Author Index445Subject Index of Mathematical Appendix455Subject Index461Fundamental and Astronomical Constants and Units493
784 citations
TL;DR: In this paper, a method for measuring the gravitational lensing induced distortion of distant background galaxies is proposed, where the authors locate the galaxies and measure a 2-component ''polarisation'' or ellipticity statistic whose expectation value should be proportional to the gravitational shear.
Abstract: We develop and test a method for measuring the gravitational lensing induced distortion of faint background galaxies. We first describe how we locate the galaxies and measure a 2-component `polarisation' or ellipticity statistic $e_\alpha$ whose expectation value should be proportional to the gravitational shear $\gamma_\alpha$. We then show that an anisotropic instrumental psf perturbs the polarisation by $\delta e_\alpha = P^s_{\alpha\beta} p_\beta$, where $p_\alpha$ is a measure of the psf anisotropy and $P^s_{\alpha\beta}$ is the `linearised smear polarisability tensor'. By estimating $P^s_{\alpha\beta}$ for each object we can determine $p_\alpha$ from the foreground stars and apply a correction $-P^s_{\alpha\beta}p_\beta$ to the galaxies. We test this procedure using deep high-resolution images from HST which are smeared with an anisotropic psf and then have noise added to simulate ground-based observations. We find that the procedure works very well. A similar analysis yields a linear shear polarisability tensor $P^\gamma_{\alpha\beta}$ which describes the response to a gravitational shear. This calibrates the polarisation-shear relation, but only for galaxies which are well resolved. To empirically calibrate the effect of seeing on the smaller galaxies we artificially stretch HST images to simulate lensing and then degrade them as before. These experiments provide a rigorous and exacting test of the method under realistic conditions. They show that it is possible to remove the effect of instrumental psf anisotropy, and that the method provides an efficient and quantitative measurement of the gravitational shear.
767 citations
TL;DR: In this paper, the authors present an implementation of smoothed particle hydrodynamics (SPH) in an adaptive-mesh PPPM algorithm, which evolves a mixture of purely gravitational particles and gas particles.
Abstract: We present an implementation of Smoothed Particle Hydrodynamics (SPH) in an adaptive-mesh PPPM algorithm. The code evolves a mixture of purely gravitational particles and gas particles. The code retains the desirable properties of previous PPPM--SPH implementations; speed under light clustering, naturally periodic boundary conditions and accurate pairwise forces. Under heavy clustering the cycle time of the new code is only 2--3 times slower than for a uniform particle distribution, overcoming the principal disadvantage of previous implementations\dash a dramatic loss of efficiency as clustering develops. A 1000 step simulation with 65,536 particles (half dark, half gas) runs in one day on a Sun Sparc10 workstation. The choice of time integration scheme is investigated in detail. A simple single-step Predictor--Corrector type integrator is most efficient. A method for generating an initial distribution of particles by allowing a a uniform temperature gas of SPH particles to relax within a periodic box is presented. The average SPH density that results varies by $\sim\pm1.3$\%. We present a modified form of the Layzer--Irvine equation which includes the thermal contribution of the gas together with radiative cooling. Tests of sound waves, shocks, spherical infall and collapse are presented. Appropriate timestep constraints sufficient to ensure both energy and entropy conservation are discussed. A cluster simulation, repeating Thomas and
258 citations
TL;DR: The analysis is discussed in terms of wormholes, and the observational test proposed is more generally a search for compact negative mass objects of any origin, recommending that MACHO search data be analyzed for GNACHO's.
Abstract: Once quantum mechanical effects are included, the hypotheses underlying the positive mass theorem of classical general relativity fail. As an example of the peculiarities attendant upon this observation, a wormhole mouth embedded in a region of high mass density might accrete mass, giving the other mouth a net [ital negative] mass of unusual gravitational properties. The lensing of such a gravitationally negative anomalous compact halo object (GNACHO) will enhance background stars with a time profile that is observable and qualitatively different from that recently observed for massive compact halo objects (MACHO's) of positive mass. While the analysis is discussed in terms of wormholes, the observational test proposed is more generally a search for compact negative mass objects of any origin. We recommend that MACHO search data be analyzed for GNACHO's.
218 citations
TL;DR: An Einstein-Hilbert-dilaton action for gravity coupled to various types of Abelian and non-Abelian gauge fields in a spatially finite system is considered and a form of the first law of black hole thermodynamics is found for black holes with the gauge fields considered here.
Abstract: We consider an Einstein-Hilbert-dilaton action for gravity coupled to various types of Abelian and non-Abelian gauge fields in a spatially finite system. These include Yang-Mills fields and Abelian gauge fields with three-form and four-form field strengths. We obtain various quasilocal quantities associated with these fields, including their energy and angular momentum, and develop methods for calculating conserved charges when a solution possesses sufficient symmetry. For stationary black holes, we find an expression for the entropy from the microcanonical form of the action. We also find a form of the first law of black hole thermodynamics for black holes with the gauge fields of the type considered here.
198 citations
CERN1
TL;DR: In this article, the one-loop effective action for non-zero U(1) or chromomagnetic fields as well as gravitational and axionic-dilatonic fields were derived.
185 citations
01 Jan 1995
TL;DR: In this article, a generalized sum-over-histories quantum theory for quantum cosmology is presented, which does not require either a preferred notion of time or a definition of measurement.
Abstract: These are the author's lectures at the 1992 Les Houches Summer School, "Gravitation and Quantizations". They develop a generalized sum-over-histories quantum mechanics for quantum cosmology that does not require either a preferred notion of time or a definition of measurement. The "post-Everett" quantum mechanics of closed systems is reviewed. Generalized quantum theories are defined by three elements (1) the set of fine-grained histories of the closed system which are its most refined possible description, (2) the allowed coarse grainings which are partitions of the fine-grained histories into classes, and (3) a decoherence functional which measures interference between coarse grained histories. Probabilities are assigned to sets of alternative coarse-grained histories that decohere as a consequence of the closed system's dynamics and initial condition. Generalized sum-over histories quantum theories are constructed for non-relativistic quantum mechanics, abelian gauge theories, a single relativistic world line, and for general relativity. For relativity the fine-grained histories are four-metrics and matter fields. Coarse grainings are four-dimensional diffeomorphism invariant partitions of these. The decoherence function is expressed in sum-over-histories form. The quantum mechanics of spacetime is thus expressed in fully spacetime form. The coarse-grainings are most general notion of alternative for quantum theory expressible in spacetime terms. Hamiltonian quantum mechanics of matter fields with its notion of unitarily evolving state on a spacelike surface is recovered as an approximation to this generalized quantum mechanics appropriate for those initial conditions and coarse-grainings such that spacetime geometry
179 citations
TL;DR: A fitting factor (FF), as a quantitative measure of how well the best template in a family ``fits'' a hypothetical gravitational waveform, in the presence of a specific detector noise spectrum, is introduced.
Abstract: Searches for gravitational waves with the LIGO-VIRGO-GEO detector network will require families of ``search templates'' with which to cross correlate the noisy detectors' output. This paper introduces a fitting factor (FF), as a quantitative measure of how well the best template in a family ``fits'' a hypothetical gravitational waveform, in the presence of a specific detector noise spectrum. An FF0.9 corresponds to a 27% reduction in the event rate of the relevant signals; therefore a family of templates that leads to FF's below 0.9 should be considered inadequate. The FF is used to explore the adequateness of several families as search templates for gravitational waves from compact inspiraling binaries. The binaries are taken to move in circular orbits, and the ``advanced LIGO noise spectrum'' is assumed for the detectors. We first study the acceptability of the simplest three-parameter template family, the so-called ``Newtonian family.'' From previous studies by Finn, Kr\'olak, Kokotas, Sch\"afer, Dhurandar, and Balasubramanian, we infer that post-Newtonian effects in the true waveforms of binaries with vanishing spins cause the Newtonian family to have an unacceptable low FF (\ensuremath{\sim}0.6 to 0.8). We then study the influence of waveform modulations caused by spin-induced orbital precession, and we isolate the modulation effects from other post-Newtonian effects by pretending that the true signals are pure Newtonian with modulation. Many different parameters influence the precession and then the waveform modulation.A wide range of parameter values is explored, and intuition is developed into which parameters most strongly influence the FF. It is shown that the unmodulated Newtonian template family works quite well (FFg0.9 for almost all parameter values) in searches for the modulated Newtonian signal from two 1.4${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ neutron stars (NS's) with one of them maximally spinning. By contrast, for a maximally spinning 10${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ black hole (BH) with a nonrotating 1.4${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ NS, the Newtonian template family produces FF0.9 for more than half of all the binaries' orientations, if the spin and orbital angular momenta are misaligned by 30\ifmmode^\circ\else\textdegree\fi{}. We introduce a new four-parameter template family, which has the form of the nonmodulated ${\mathrm{post}}^{1}$-Newtonian signal from a zero-spin-binary. Although, there is a substantial improvement of the FF's for a spin-modulated Newtonian signal, the FF's for nonmodulated ${\mathrm{post}}^{1.5}$-Newtonian waveforms are still very poor (\ensuremath{\sim}0.5--0.8). Therefore we propose another four-parameter template family that has the same form as a nonmodulated ${\mathrm{post}}^{1.5}$-Newtonian signal with all the spin-related parameters stripped off. This template family works ${\mathrm{post}}^{1.5}$-Newtonian modulated signals quite well. These results suggest that, in a few years, when waveforms have been computed up to ${\mathrm{post}}^{3}$-Newtonian order, a good template family will be the four-parameter ${\mathrm{post}}^{3}$-Newtonian waveforms for zero-spin binaries, augmented by some appropriate modulations to deal with misaligned, rapidly spinning BH-NS systems. Finally, we extend our investigations to the space-based low-frequency LISA detector.
164 citations
TL;DR: In this paper, it was shown that the static spherically symmetric solutions to the Brans-Dicke theory of gravitation give rise either to a naked singularity or to a post Newtonian parameter γ 1.
Abstract: It is shown that the static spherically symmetric solutions to the Brans-Dicke theory of gravitation give rise either to a naked singularity if the post Newtonian parameter γ 1.
161 citations
127 citations
TL;DR: In this paper, a new formalism is presented which allows to derive the general Lagrangian dynamical equations for the motion of gravitating particles in a non-flat Friedmann universe with arbitrary density parameter and no cosmological constant.
Abstract: We present a new formalism which allows to derive the general Lagrangian dynamical equations for the motion of gravitating particles in a non--flat Friedmann universe with arbitrary density parameter $\Omega$ and no cosmological constant. We treat the set of particles as a Newtonian collisionless fluid. The non--linear dynamical evolution of the fluid element trajectories is then described up to the third--order expansion in Lagrangian coordinates. This work generalizes recent investigations carried out by Bouchet \etal (1992) and Buchert (1994).
TL;DR: If such objects can exist, they will have the first realization of the universal gravitational force which repels all particles with the strength proportional to their mass and therefore can be associated with antigravity.
Abstract: We study special points in the moduli space of vacua at which supersymmetric electric solutions of the heterotic string theory become massless. We concentrate on configurations for which supersymmetric non-renormalization theorem is valid. Those are ten-dimensional supersymmetric string waves and generalized fundamental strings with $SO(8)$ holonomy group. >From these we find the four dimensional spherically symmetric configurations which saturate the BPS bound, in particular near the points of the vanishing ADM mass. The non-trivial massless supersymmetric states in this class exist only in the presence of non-Abelian vector fields. We also find a new class of supersymmetric massive solutions, closely related to the massless ones. A distinctive property of all these objects, either massless or massive, is the existence of gravitational repulsion. They reflect all particles with nonvanishing mass and/or angular momentum, and therefore they can be called white holes, in contrast to black holes which tend to absorb particles of all kinds. If such objects can exist, we will have the first realization of the universal gravitational force which repels all particles with the strength proportional to their mass and therefore can be associated with antigravity.
TL;DR: Observations of the perturbation spectra produced during inflation are shown to be used to constrain the parameters of general scalar-tensor theories of gravity, which include both an inflaton and dilaton field.
Abstract: We show how observations of the perturbation spectra produced during inflation may be used to constrain the parameters of general scalar-tensor theories of gravity, which include both an inflaton and dilaton field. An interesting feature of these models is the possibility that the curvature perturbations on super-horizon scales may not be constant due to non-adiabatic perturbations of the two fields. Within a given model, the tilt and relative amplitude of the scalar and tensor perturbation spectra gives constraints on the parameters of the gravity theory, which may be comparable with those from primordial nucleosynthesis and post-Newtonian experiments.
TL;DR: In this article, the authors considered the problem of constructing a non-singular inflationary universe in stringy gravity via branch changing, from a previously superexponentially expanding phase to an FRW-like phase, and obtained a no-go theorem which rules out the efficient scenario of branch changing catalyzed by dilaton potential and stringy fluid sources.
TL;DR: A mathematically consistent procedure for coupling quasiclassical and quantum variables through coupled Hamilton-Heisenberg equations of motion is derived from a variational principle, which leads to a natural candidate for a theory of gravity coupled to quantized matter in which the gravitational field is not quantized.
Abstract: A mathematically consistent procedure for coupling quasiclassical and quantum variables through coupled Hamilton-Heisenberg equations of motion is derived from a variational principle. During evolution, the quasiclassical variables become entangled with the quantum variables with the result that the value of the quasiclassical variables depends on the quantum state. This provides a formalism to compute the backreaction of any quantum system on a quasiclassical one. In particular, it leads to a natural candidate for a theory of gravity coupled to quantized matter in which the gravitational field is not quantized.
TL;DR: In this article, the authors argue that any modification of general relativity which is completely nonsingular cannot have a stable ground state, and apply this argument to quantum theories of gravity.
Abstract: We point out that spacetime singularities play a useful role in gravitational theories by eliminating unphysical solutions. In particular, we argue that any modification of general relativity which is completely nonsingular cannot have a stable ground state. This argument applies both to classical extensions of general relativity, and to candidate quantum theories of gravity.
TL;DR: In this article, the existence of extra dimensions to spacetime can be tested astrophysically using Kaluza-Klein theory, which is a natural extension of Einsteins's general relativity.
Abstract: The possible existence of extra dimensions to spacetime can be tested astrophysically using Kaluza-Klein theory, which is a natural extension of Einsteins's general relativity. In the simplest version of the theory, there is a standard class of five-dimensional solutions that are analogous to the four-dimensional Schwarzschild solution. However, even a small departure of the extra dimension from flatness affects the first or dominant part of the potential, making it possible to test for the existence of an extra dimension. Data from the solar system indicate that in our region of space the terms due to the fifth dimension are small (less than or equal to 0.1%) compared to those due to the usual for dimensions of spacetime. However, the parameters of Kaluza-Klein theory are not universal constants and can vary from place to place depending on local physics. Hence other astrophysical systems may serve as better laboratories for investigating the possible existence of extra dimensions.
TL;DR: In this article, a consistent description of spinning strings with dislocations (chiral strings) as a missing part of the spacetime manifold (spacetime defect) is achieved by introducing a line of torsion along the string.
Abstract: A consistent description of spinning strings with dislocations (chiral strings) as a missing part of the spacetime manifold (spacetime defect) is achieved by introducing a line of torsion along the string. Also, the definition of a spin-dislocation tensor associated with the chiral string allows its interpretation in the context of the Einstein--Cartan theory of gravitation. Some generalizations, as well as the Dirac equations, are briefly discussed. In particular, we argue that the behaviour of the fermions near the chiral string can be used to test the torsion hypothesis.
TL;DR: A class of higher-derivative interactions for the gravitational and electromagnetic fields which produce dispersive photon propagation is found which is illustrated by calculating the energy-dependent contribution to the deflection of light rays.
Abstract: Limits for the applicability of the equivalence principle are considered in the context of low-energy effective field theories. In particular, we find a class of higher-derivative interactions for the gravitational and electromagnetic fields which produce dispersive photon propagation. The latter is illustrated by calculating the energy-dependent contribution to the deflection of light rays.
TL;DR: In this article, a suitable modification of Utiyama's method for gauging the projective realization of the Galilei group associated with the free mass-point, together with connections between the consequent 11 external gauge fields and known facts about Galilean and Newtonian geometrical structures, are discussed from a unified point of view.
Abstract: Newton's standard theory of gravitation is reformulated in terms of a generally Galilei-covariant action principle as a gauge theory of the extended Galilei group. A suitable modification of Utiyama's method for gauging the projective realization of the Galilei group associated with the free mass-point, together with the connections between the consequent 11 external gauge fields and known facts about Galilean and Newtonian geometrical structures, are discussed from a unified point of view. Then the problem of the existence of an action principle for the dynamical evolution of the gauge fields is analysed. Since it is not known how to extend Utiyama's method from the case of `invariance' to the case of `quasi-invariance, modulo the equations of motion', which turns out to be the key factor in the Galilean case, an action principle is derived, starting from a suitable power expansion of the 4-metric tensor, as a contraction, for , of the ADM-De-Witt action of general relativity. The Galilean action depends on 27 fields (i.e. it contains 16 auxiliary fields besides the 11 gauge fields) and is indeed quasi-invariant, modulo the equations of motion under general Galilean coordinate transformations. The physical equivalence of this theory and Newton's theory of gravity is shown explicitly, by analysing its first- and second-class constraints. Finally, we discuss the feasibility of a symplectic reduction of the 27-fields theory to a minimal theory depending on only the 11 gauge fields, in the sense of Utiyama's method.
TL;DR: In this article, the properties of dense matter in neutron stars and supernovae in the relativistic mean field (RMF) theory with non-linear σ and ω terms were studied.
TL;DR: In this paper, a systematic formulation of the higher genus expansion in topological string theory is considered and a simple way of evaluating genus zero correlation functions is developed for higher genera.
Abstract: A systematic formulation of the higher genus expansion in topological string theory is considered. We also develop a simple way of evaluating genus zero correlation functions. At higher genera we derive some interesting formulas for the free energy in the A1 and A2 models. We present some evidence that topological minimal models associated with Lie algebras other than the A-D-E type do not have a consistent higher genus expansion beyond genus one. We also present some new results on the CP1 model at higher genera.
TL;DR: In this paper, the gravitationally dressed four-point correlation function of products of left and right fermions is shown to exhibit a logarithmic short distance singularity, instead of the power-law singularity in the absence of gravity.
TL;DR: In this paper, the Friedmann-Robertson-Walker cosmologies in BransDicke theory were analyzed, where a scalar field is coupled to gravity and matter is modelled by a -law perfect fluid, including false-vacuum energy.
TL;DR: In this paper, the problem of solving perturbatively the equations describing the evolution of self-gravitating collisionless matter in an expanding universe was simplified when directly formulated in terms of the gravitational and velocity potentials, rather than approximately, even for cosmological models with arbitrary density parameter.
Abstract: The problem of solving perturbatively the equations describing the evolution of self-gravitating collisionless matter in an expanding universe considerably simplifies when directly formulated in terms of the gravitational and velocity potentials: the problem can be solved {\it exactly}, rather than approximately, even for cosmological models with arbitrary density parameter $\Omega$. The Eulerian approach we present here allows to calculate the higher-order moments of the initially Gaussian density and velocity fields: in particular, we compute the gravitationally induced skewness of the density and velocity-divergence fields for any value of $\Omega$, confirming the extremely weak $\Omega$-dependence of the skewness previously obtained via Lagrangian perturbation theory. Our results show that the separability assumption of higher-order Eulerian perturbative solutions is restricted to the Einstein-de Sitter case only.
TL;DR: In this paper, a nonlinear quantum theory of Newtonian gravity consistent with an objective interpretation of the wave function is developed, inspired by the ideas of Schrodinger, and Bell, and a dimensional reduction procedure to map complex wavefunctions in configuration space onto a family of observable fields in space-time.
Abstract: We develop a nonlinear quantum theory of Newtonian gravity consistent with an objective interpretation of the wavefunction. Inspired by the ideas of Schrodinger, and Bell, we seek a dimensional reduction procedure to map complex wavefunctions in configuration space onto a family of observable fields in space-time. Consideration of quasi-classical conservation laws selects the reduced one-body quantities as the basis for an explicit quasi-classical coarse-graining. These we interpret as describing the objective reality of the laboratory. Thereafter, we examine what may stand in the role of the usual Copenhagen observer to localise this quantity against macroscopic dispersion. Only a tiny change is needed, via a generically attractive self-potential. A nonlinear treatment of gravitational self-energy is thus advanced. This term sets a scale for all wavepackets. The Newtonian cosmology is thus closed, without need of an external observer. Finally, the concept of quantisation is re-interpreted as a nonlinear eigenvalue problem. To illustrate, we exhibit an elementary family of gravitationally self-bound solitary waves. Contrasting this theory with its canonically quantised analogue, we find that the given interpretation is empirically distinguishable, in principle. This result encourages deeper study of nonlinear field theories as a testable alternative to canonically quantised gravity.
TL;DR: The masses of the black holes are able to compute the masses from the measurements of their apparent horizons, as well as the total energy radiated and find their sum to be in excellent agreement with the ADM mass.
Abstract: We have developed a numerical code to study the evolution of distorted, rotating black holes. This code is used to evolve a new family of black hole initial data sets corresponding to distorted ``Kerr'' holes with a wide range of rotation parameters, and distorted Schwarzschild black holes with odd-parity radiation. Rotating black holes with rotation parameters as high as $a/m=0.87$ are evolved and analyzed in this paper. The evolutions are generally carried out to about $t=100M$, where $M$ is the ADM mass. We have extracted both the even- and odd-parity gravitational waveforms, and find the quasinormal modes of the holes to be excited in all cases. We also track the apparent horizons of the black holes, and find them to be a useful tool for interpreting the numerical results. We are able to compute the masses of the black holes from the measurements of their apparent horizons, as well as the total energy radiated and find their sum to be in excellent agreement with the ADM mass.