arXiv subjects

Jorge Pullin

Publications and source records attributed to Jorge Pullin.

At least 181 records · Page 10Linked to original sources

arXiv1996

Matters of Gravity, the newsletter of the APS TG on gravitation

Contents: APS Topical Group in Gravitation News: April 1997 Joint APS/AAPT Meeting Research briefs: GEO600 by Karsten Danzmann Black hole microstates in string theory by Gary Horowitz LIGO project status by Stan Whitcomb The Hamiltonian constraint of quantum gravity and loops by John Baez Conference reports: International conference on gravitational waves by Valeria Ferrari PCGM12/KKfest by Richard Price First International LISA Symposium by Robin Stebbins Schroedinger Institute Workshop by Abhay Ashtekar Relativistic Astrophysics at Bad Honnef by Hans-Peter Nollert Intermediate binary black hole workshop by Sam Finn Quantum Gravity in the Southern Cone by Rodolfo Gambini Report on the Spring APS Meeting by Fred Raab and Beverly Berger

gr-qc↗

arXiv1996

The collision of boosted black holes

We study the radiation from a collision of black holes with equal and opposite linear momenta. Results are presented from a full numerical relativity treatment and are compared with the results from a ``close-slow'' approximation. The agreement is remarkable, and suggests several insights about the generation of gravitational radiation in black hole collisions.

gr-qc↗

arXiv1996

Lattice knot theory and quantum gravity in the loop representation

We present an implementation of the loop representation of quantum gravity on a square lattice. Instead of starting from a classical lattice theory, quantizing and introducing loops, we proceed backwards, setting up constraints in the lattice loop representation and showing that they have appropriate (singular) continuum limits and algebras. The diffeomorphism constraint reproduces the classical algebra in the continuum and has as solutions lattice analogues of usual knot invariants. We discuss some of the invariants stemming from Chern--Simons theory in the lattice context, including the issue of framing. We also present a regularization of the Hamiltonian constraint. We show that two knot invariants from Chern--Simons theory are annihilated by the Hamiltonian constraint through the use of their skein relations, including intersections. We also discuss the issue of intersections with kinks. This paper is the first step towards setting up the loop representation in a rigorous, computable setting.

gr-qc↗

arXiv1996

Canonical quantum gravity with new variables and loops: a report

This is a brief and updated summary of a talk given at the International Conference on Gravitation and Cosmology that took place in Poona in December 1995. It is very brief and is mostly intended as a guide to current literature, or to keep people updated only in very broad terms on the latest developments in the subject.

gr-qc↗

arXiv1996

Second order perturbations of a Schwarzschild black hole

We study the even-parity $\ell=2$ perturbations of a Schwarzschild black hole to second order. The Einstein equations can be reduced to a single linear wave equation with a potential and a source term. The source term is quadratic in terms of the first order perturbations. This provides a formalism to address the validity of many first order calculations of interest in astrophysics.

gr-qc↗

arXiv1996

The general solution of the quantum Einstein equations?

We suggest how to interpret the action of the quantum Hamiltonian constraint of general relativity in the loop representation as a skein relation on the space of knots. Therefore, by considering knot polynomials that are compatible with that skein relation, one guarantees that all the quantum Einstein equations are solved. We give a particular example of such invariant and discuss the consistency of the constraint algebra in this approach.

gr-qc↗

arXiv1996

Variational derivation of exact skein relations from Chern--Simons theories

The expectation value of a Wilson loop in a Chern--Simons theory is a knot invariant. Its skein relations have been derived in a variety of ways, including variational methods in which small deformations of the loop are made and the changes evaluated. The latter method only allowed to obtain approximate expressions for the skein relations. We present a generalization of this idea that allows to compute the exact form of the skein relations. Moreover, it requires to generalize the resulting knot invariants to intersecting knots and links in a manner consistent with the Mandelstam identities satisfied by the Wilson loops. This allows for the first time to derive the full expression for knot invariants that are suitable candidates for quantum states of gravity (and supergravity) in the loop representation. The new approach leads to several new insights in intersecting knot theory, in particular the role of non-planar intersections and intersections with kinks.

hep-th↗

arXiv1996

Matters of Gravity, Newsletter of the APS TGG on gravitation, number 7

Contents: Editorial, J. Pullin Report from the APS TGG, Beverly Berger We hear that..., J. Pullin LIGO project status, S. Whitcomb General relativity survives another test, C. Will Macroscopic deviations from Hawking radiation? L. Smolin Event horizons and topological censorship, E. Seidel Critical behavior in black hole collapse, J. Horne Third Texas Workshop on 3D Numerical Relativity, P. Laguna ICGC-95, M.A.H. MacCallum The Josh Goldberg Symposium, P. Saulson Summer school in Bad Honnef, H.-P. Nollert Fifth Annual Midwest Relativity Conference, J. Romano Volga-7 '95, A. Aminova, D. Brill.

gr-qc↗

arXiv1996

Analytic approximations to the spacetime of a critical gravitational collapse

We present analytic expressions that approximate the behavior of the spacetime of a collapsing spherically symmetric scalar field in the critical regime first discovered by Choptuik. We find that the critical region of spacetime can usefully be divided into a ``quiescent'' region and an ``oscillatory'' region, and a moving ``transition edge'' that separates the two regions. We find that in each region the critical solution can be well approximated by a flat spacetime scalar field solution. A qualitative nonlinear matching of the solutions across the edge yields the right order of magnitude for the oscillations of the discretely self-similar critical solution found by Choptuik.

gr-qc↗

arXiv1995

Towards a loop representation for quantum canonical supergravity

We study several aspects of the canonical quantization of supergravity in terms of the Asthekar variables. We cast the theory in terms of a $GSU(2)$ connection and we introduce a loop representation. The solution space is similar to the loop representation of ordinary gravity, the main difference being the form of the Mandelstam identities. Physical states are in general given by knot invariants that are compatible with the $GSU(2)$ Mandelstam identities. There is an explicit solution to all the quantum constraint equations connected with the Chern-Simons form, which coincides exactly with the Dubrovnik version of the Kauffman Polynomial. This provides for the first time the possibility of finding explicit analytic expressions for the coefficients of that knot polynomial.

hep-th↗

arXiv1995

A rigorous solution of the quantum Einstein equations

We show that the second coefficient of the Conway knot polynomial is annihilated by the Hamiltonian constraint of canonically quantized general relativity in the loop representation. The calculations are carried out in a fully regularized lattice framework. Crucial to the calculation is the explicit form of the skein relations of the second coefficient, which relate it to the Gauss linking number. Contrary to the lengthy formal continuum calculation, the rigorous lattice version can be summarized in a few pictures.

gr-qc↗

arXiv1995

MATTERS OF GRAVITY, The newsletter of the APS Topical Group on Gravitation

Contents: -Report from the APS Topical Group in Gravitation, Beverly Berger -Some remarks on the passing of S. Chandrasekhar, Robert Wald -LIGO Project Status, Syd Meshkov and Stan Whitcomb -New Hyperbolic forms of the Einstein Equations, Andrew Abrahams -Massless Black Holes, Gary Horowitz -A plea for theoretical help from the gravity wave co-op, William Hamilton -Why Quantum Cosmologists are Interested in Quantum Mechanics, James Hartle -Probing the Early Universe with the Cosmic Microwave Background, Rahul Dave and Paul Steinhardt -G measurements, Riley Newman -Is general relativity about null surfaces?, Carlo Rovelli -ITP program solicitation, James Hartle -7th Gregynog workshop in general relativity, Miguel Alcubierre -Third Annual Penn State Conference: Astrophysical Sources of Gravitational Waves, Curt Cutler -General news from GR14, Abhay Ashtekar -VIth Canadian General Relativity Conference, Jack Gegenberg

gr-qc↗

arXiv1995

Head-on collision of two black holes: comparison of different approaches

A benchmark problem for numerical relativity has been the head-on collision of two black holes starting from the ``Misner initial data,'' a closed form momentarily stationary solution to the constraint equations with an adjustable closeness parameter $μ_0$. We show here how an eclectic mixture of approximation methods can provide both an efficient means of determining the time development of the initial data and a good understanding of the physics of the problem. When the Misner data is chosen to correspond to holes initially very close together, a common horizon surrounds both holes and the geometry exterior to the horizon can be treated as a non-spherical perturbation of a single Schwarzschild hole. When the holes are initially well separated the problem can be treated with a different approximation scheme, ``the particle-membrane method.'' For all initial separations, numerical relativity is in principle applicable, but is costly and of uncertain accuracy. We present here a comparison of the different approaches. We compare waveforms, for $\ell=2$ and $\ell=4$ radiation, for different values of $μ_0$, from the three different approaches to the problem.

gr-qc↗

arXiv1995

The space of states of quantum gravity in terms of loops and extended loops: some remarks

This article reviews the status of several solutions to all the constraints of quantum gravity that have been proposed in terms of loops and extended loops. We discuss pitfalls of several of the results and in particular discuss the issues of covariance and regularization of the constraints in terms of extended loops. We also propose a formalism for ``thickened out loops'' which does not face the covariance problems of extended loops and may allow to regularize expressions in a consistent manner.

gr-qc↗

arXiv1995

Matters of Gravity, a newsletter for the gravity community

Table of contents: -Editorial and Correspondents Gravity news: -LISA Recommended to ESA as Possible New Cornerstone Mission, Peter Bender. -LIGO Project News, Stan Whitcomb. Research briefs: -Some Recent Work in General Relativistic Astrophysics, John Friedman. -Pair Creation of Black Holes, Gary Horowitz. -Conformal Field Equations and Global Properties of Spacetimes, Bernd Schmidt Conference reports: -Aspen Workshop on Numerical Investigations of Singularities in GR, Susan Scott -Second Annual Penn State Conference: Quantum Geometry, Abhay Ashtekar -First Samos Meeting, Spiros Cotsakis and Dieter Brill -Aspen Conference on Gravitational Waves and Their Detection, Syd Meshkov

gr-qc↗

arXiv1994

Is there a connection between no-hair behavior and universality in gravitational collapse?

We apply linear perturbation theory to the study of the universality and criticality first observed by Choptuik in gravitational collapse. Since these are essentially nonlinear phenomena our attempt is only a rough approximation. In spite of this, universal behavior of the final black hole mass is observed with an exponent of 1/2, slightly higher than the observed value of 0.367. The universal behavior is rooted in the universal form that in-falling perturbations on black holes have at the horizon.

gr-qc↗

arXiv1994

MATTERS OF GRAVITY, a newsletter for the gravity community, Number 4

Table of contents Editorial. Gravity News: Report on the APS topical group in gravitation, Beverly Berger. Research briefs: Gravitational microlensing and the search for dark matter, Bohdan Paczynski. Laboratory gravity: the G mystery, Riley Newman. LIGO project update, Stan Whitcomb. Conference Reports PASCOS '94, Peter Saulson. The Vienna Meeting, P. Aichelburg, R. Beig. The Pitt binary black hole grand challenge meeting, Jeff Winicour. International symposium on experimental gravitation at Pakistan,Munawar Karim 10th Pacific coast gravity meeting, Jim Isenberg.

gr-qc↗

arXiv1994

The constraint algebra of quantum gravity in the loop representation

We study the algebra of constraints of quantum gravity in the loop representation based on Ashtekar's new variables. We show by direct computation that the quantum commutator algebra reproduces the classical Poisson bracket one, in the limit in which regulators are removed. The calculation illustrates the use of several computational techniques for the loop representation.

gr-qc↗