GGR News: New Matters of Gravity Correspondents, by David Garfinkle we hear that..., by David Garfinkle Research Briefs: Numerical Relativity Studies of Black Hole Kicks, by Pablo Laguna Conference...
The motion of galaxy clusters in inhomogeneous cosmologies (2009)
Lemaitre-Tolman-Bondi inhomogeneous spacetimes can be used as a cosmological model to account for the type Ia supernova data. However, such models also give rise to large velocities of galaxy...
Spikes in the Mixmaster regime of G_2 cosmologies (2009)
Lim, Woei Chet, Andersson, Lars, Garfinkle, David, Pretorius, Frans
We produce numerical evidence that spikes in the Mixmaster regime of G_2 cosmologies are transient and recurring, supporting the conjecture that the generalized Mixmaster behavior is asymptotically...
GGR News: o GGR program at the APS meeting in Denver, by David Garfinkle o we hear that ..., by David Garfinkle o 400 years ago, by David Garfinkle Conference reports: o The 24th Texas Symposium on...
Spikes in the Mixmaster regime of G2 cosmologies (2009)
Lim, Woei Chet, Andersson, Lars, Garfinkle, David, Pretorius, Frans
We produce numerical evidence that spikes in the Mixmaster regime of G2 cosmologies are transient and recurring, supporting the conjecture that the generalized Mixmaster behavior is asymptotically...
The Parallelometer: a mechanical device to study curvature (2008)
Rojo, Alberto G., Garfinkle, David, Gil, Salvador
A simple mechanical device is introduced, the parallelometer, that can be used to measure curvatures of surfaces. The device can be used as a practical illustration of parallel transport of a vector...
Evolution to a smooth universe in an ekpyrotic contracting phase with w > 1 (2008)
Garfinkle, David, Lim, Woei Chet, Pretorius, Frans, Steinhardt, Paul J.
A period of slow contraction with equation of state w > 1, known as an ekpyrotic phase, has been shown to flatten and smooth the universe if it begins the phase with small perturbations. In this...
Numerical simulations of general gravitational singularities (2008)
This paper covers some of the current techniques and issues involved in performing numerical simulations of the formation of singularities.
GGR News: GGR program at the APS meeting in St. Louis we hear that... by David Garfinkle 100 years ago, by David Garfinkle Research Briefs: The Torsion Pendulum's Contribution to Dark Energy, by Bill...
Evolution to a smooth universe in an ekpyrotic contracting phase with w>1 (2008)
Garfinkle, David, Lim, Woei Chet, Pretorius, Frans, Steinhardt, Paul J.
A period of slow contraction with equation of state w>1, known as an ekpyrotic phase, has been shown to flatten and smooth the universe if it begins the phase with small perturbations. In this paper,...
GGR News: -we hear that..., by David Garfinkle -News from the GRG Society, by Abhay Ashtekar -LIGO/GEO/Virgo work together, by Peter Saulson -GWIC Ten Years on, by Stan Whitcomb Research Briefs:...
The Modelling of Degenerate Neck Pinch Singularities in Ricci Flow by Bryant Solitons (2007)
Garfinkle, David, Isenberg, James
In earlier work, carrying out numerical simulations of the Ricci flow of families of rotationally symmetric geometries on $S3$, we have found strong support for the contention that (at least in the...
Comments on Bona-Masso type slicing conditions in long-term black hole evolutions (2007)
Garfinkle, David, Gundlach, Carsten, Hilditch, David
We review in generality why time-independent endstates can be reached in black hole and collapse simulations, with and without excision. We characterise the Killing states of the Bona-Masso slicing...
Numerical simulations of gravitational collapse in Einstein-aether theory (2007)
Garfinkle, David, Eling, Christopher, Jacobson, Ted
We study gravitational collapse of a spherically symmetric scalar field in Einstein-aether theory (general relativity coupled to a dynamical unit timelike vector field). The initial value formulation...
GGR News: - The View from the NSF, by Beverly Berger - GGR Program at the APS meeting in Jacksonville we hear that..., by David Garfinkle - 100 years ago, by David Garfinkle Research Briefs: - The...
Research Briefs: Singularity Avoidance in Canonical Quantum Gravity, by Viqar Husain What's New in LIGO, by David Shoemaker Conference reports: Scanning New Horizons: GR Beyond 4 dimensions, by...
Inhomogeneous spacetimes as a dark energy model (2006)
Tolman-Bondi inhomogeneous spacetimes are used as a cosmological model for type Ia supernova data. It is found that with certain parameter choices the model fits the data as well as the standard...
Gauge invariance and the detection of gravitational radiation (2005)
The detection of gravitational radiation raises some subtle issues having to do with the coordinate invariance of general relativity. This paper explains these issues and their resolution by using an...
The need for dark matter in galaxies (2005)
Cooperstock and Tieu have proposed a model to account for galactic rotation curves without invoking dark matter. I argue that no model of this type can work.
Well-posedness of the scale-invariant tetrad formulation of the vacuum Einstein equations (2005)
Garfinkle, David, Gundlach, Carsten
We show that, with a small modification, the formulation of the Einstein equations of Uggla et al, which uses tetrad variables normalized by the expansion, is a mixed symmetric hyperbolic/parabolic...
Numerical simulations of stiff fluid gravitational singularities (2005)
Curtis, Joshua, Garfinkle, David
Numerical simulations of the approach to the singularity in spacetimes with stiff fluid matter are presented here. The spacetimes examined have no symmetries and can be regarded as representing the...
Well-posedness of the scale-invariant tetrad formulation of the vacuum Einstein equations (2005)
Garfinkle, David, Gundlach, Carsten
We show that with a small modification, the formulation of the Einstein equations of Uggla et al, which uses tetrad variables normalised by the expansion, is a mixed symmetric hyperbolic/parabolic...
Gravitational collapse in anti de Sitter space (2004)
A numerical and analytic treatment is presented here of the evolution of initial data of the kind that was conjectured by Hertog, Horowitz and Maeda to lead to a violation of cosmic censorship. That...
The fine structure of Gowdy spacetimes (2004)
The approach to the singularity in Gowdy spacetimes consists of velocity term dominated behavior, except at a set of isolated points. At and near these points, spiky features grow. This paper reviews...
The nature of gravitational singularities (2004)
The nature of gravitational singularities, long mysterious, has now become clear through a combination of mathematical and numerical analysis. As the singularity is approached, the time derivative...
Numerical simulation of a possible counterexample to cosmic censorship (2004)
A numerical simulation is presented here of the evolution of initial data of the kind that was conjectured by Hertog, Horowitz and Maeda to be a violation of cosmic censorship. That initial data is...
Numerical simulations of generic singuarities (2003)
Numerical simulations of the approach to the singularity in vacuum spacetimes are presented here. The spacetimes examined have no symmetries and can be regarded as representing the general behavior...
Critical behavior in Ricci flow (2003)
Garfinkle, David, Isenberg, James
We use numerical techniques to study the formation of singularities in Ricci flow. Comparing the Ricci flows corresponding to a one parameter family of initial geometries on S^3 with varying amounts...
Critical collapse of a massive vector field (2003)
Garfinkle, David, Mann, Robert, Vuille, Chris
We perform numerical simulations of the critical gravitational collapse of a massive vector field. The result is that there are two critical solutions. One is equivalent to the Choptuik critical...
High velocity spikes in Gowdy spacetimes (2003)
Garfinkle, David, Weaver, Marsha
We study the behavior of spiky features in Gowdy spacetimes. Spikes with velocity initially high are, generally, driven to low velocity. Let n be any integer greater than or equal to 1. If the...
Perturbations of an exact solution for (2+1) -dimensional critical collapse (2002)
Garfinkle, David, Gundlach, Carsten
We find the perturbation spectrum of a family of spherically symmetric and continuously self-similar (CSS) exact solutions that appear to be relevant for the critical collapse of scalar field matter...
Perturbations of an exact solution for 2+1 dimensional critical collapse (2002)
Garfinkle, David, Gundlach, Carsten
We find the perturbation spectrum of a family of spherically symmetric and continuously self-similar (CSS) exact solutions that appear to be relevant for the critical collapse of scalar field matter...
Harmonic coordinate method for simulating generic singularities (2001)
This paper presents both a numerical method for general relativity and an application of that method. The method involves the use of harmonic coordinates in a 3+1 code to evolve the Einstein...
An exact solution for 2+1 dimensional critical collapse (2000)
We find an exact solution in closed form for the critical collapse of a scalar field with cosmological constant in 2+1 dimensions. This solution agrees with the numerical simulation done by Pretorius...
Numerical evolution of Brill waves (2000)
Garfinkle, David, Duncan, G. Comer
We report a numerical evolution of axisymmetric Brill waves. The numerical algorithm has new features, including (i) a method for keeping the metric regular on the axis and (ii) the use of...
Generalized entropy and Noether charge (2000)
Garfinkle, David, Mann, Robert
We find an expression for the generalized gravitational entropy of Hawking in terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime is calculated.
Existence, uniqueness and other properties of the BCT (minimal strain lapse and shift) gauge (2000)
Garfinkle, David, Gundlach, Carsten, Isenberg, James, OMurchadha, Niall
Brady, Creighton and Thorne have proposed a choice of the lapse and shift for numerical evolutions in general relativity that extremizes a measure of the rate of change of the three-metric (BCT...
Existence, uniqueness and other properties of the BCT (minimal strain lapse and shift) gauge (2000)
Garfinkle, David, Gundlach, Carsten, Isenberg, James, O'Murchadha, Niall
Brady, Creighton and Thorne (BCT) have proposed a choice of the lapse and shift for numerical evolutions in general relativity that extremizes a measure of the rate of change of the 3-metric (BCT...
Choptuik scaling in six dimensions (1999)
Garfinkle, David, Cutler, Curt, Duncan, G. Comer
We perform numerical simulations of the critical gravitational collapse of a spherically symmetric scalar field in 6 dimensions. The critical solution has discrete self-similarity. We find the...
Null infinity and an electromagnetic analog of the relativistic Kepler problem (1999)
This paper has been withdrawn by the author. It has come to my attention that most of the results reported here have already been obtained by Ludvigsen.
Metrics with distributional curvature (1999)
This paper considers metrics whose curvature tensor makes sense as a distribution. A class of such metrics, the regular metrics, was defined and studied by Geroch and Traschen. Here, we generalize...
Numerical simulations of Gowdy spacetimes on S2XS1XR (1999)
Numerical simulations are performed of the approach to the singularity in Gowdy spacetimes on S2XS1XR. The behavior is similar to that of Gowdy spacetimes on T3XR. In particular, the singularity is...
Choptuik scaling in six dimensions (1999)
Garfinkle,David, Cutler,Curt, Duncan,G. Comer
We perform numerical simulations of the critical gravitational collapse of a spherically symmetric scalar field in 6 dimensions. The critical solution has discrete self-similarity. We find the...
Choptuik scaling in six dimensions (1999)
Garfinkle, David, Cutler, Curt, Comer, Duncan G.
We perform numerical simulations of the critical gravitational collapse of a spherically symmetric scalar field in 6 dimensions. The critical solution has discrete self-similarity. We find the...
Choptuik scaling in six dimensions. (1999)
Garfinkle, David, Cutler, Curt, Comer, Duncan
We perform numerical simulations of the critical gravitational collapse of a spherically symmetric scalar field in 6 dimensions. The critical solution has discrete self-similarity. We find the...
Angular momentum near the black hole threshold in scalar field collapse (1999)
Garfinkle, David, Gundlach, Carsten, Martin-Garcia, José M.
For the formation of a black hole in the gravitational collapse of a massless scalar field, we calculate a critical exponent that governs the black hole angular momentum for slightly non-spherical...
Scale invariance and critical gravitational collapse (1998)
We examine ways to write the Choptuik critical solution as the evolution of scale invariant variables. It is shown that a system of scale invariant variables proposed by one of the authors does not...
The Singularity in Generic Gravitational Collapse Is Spacelike, Local, and Oscillatory (1998)
Berger, Beverly K., Garfinkle, David, Isenberg, James, Moncrief, Vincent, Weaver, Marsha
A longstanding conjecture by Belinskii, Khalatnikov, and Lifshitz that the singularity in generic gravitational collapse is spacelike, local, and oscillatory is explored analytically and numerically...
Scaling of curvature in sub-critical gravitational collapse (1998)
Garfinkle, David, Duncan, G. Comer
We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the...
Phenomenology of the Gowdy Universe on $T^3 \times R$ (1997)
Berger, Beverly K., Garfinkle, David
Numerical studies of the plane symmetric, vacuum Gowdy universe on $T^3 \times R$ yield strong support for the conjectured asymptotically velocity term dominated (AVTD) behavior of its evolution...
Comment on ``The Gowdy $T^3$ Cosmologies Revisited'' (1997)
Berger, Beverly K., Garfinkle, David, Moncrief, Vincent
A standard and reasonable definition of asymptotic velocity term dominance (AVTD) shows that the numerical study by Hern and Stewart (gr-qc/9708038) confirms previous results that generic Gowdy...
Numerical Study of Cosmological Singularities (1997)
Beverly K. Berger, David Garfinkle, Vincent Moncrief
The spatially homogeneous, isotropic Standard Cosmological Model appears to describe our Universe reasonably well. However, Einstein's equations allow a much larger class of cosmological...
Choptuik scaling and the scale invariance of Einstein's equation (1996)
The relationship of Choptuik scaling to the scale invariance of Einstein's equation is explored. Ordinary dynamical systems often have limit cycles: periodic orbits that are the asymptotic limit of...
Solution generating with perfect fluids (1996)
Garfinkle, David, Glass, E. N., Krisch, J. P.
We apply a technique, due to Stephani, for generating solutions of the Einstein-perfect fluid equations. This technique is similar to the vacuum solution generating techniques of Ehlers, Harrison,...
New Algorithm for Mixmaster Dynamics (1996)
Berger, Beverly K., Garfinkle, David, Strasser, Eugene
We present a new numerical algorithm for evolving the Mixmaster spacetimes. By using symplectic integration techniques to take advantage of the exact Taub solution for the scattering between...
Ricci Fall-off in Static, Globally Hyperbolic, Non-singular Spacetimes (1995)
Garfinkle, David, Harris, Steven G.
What restrictions are there on a spacetime for which the Ricci curvature is such as to produce convergence of geodesics (such as the preconditions for the Singularity Theorems) but for which there...
Choptuik scaling in null coordinates (1994)
A numerical simulation is performed of the gravitational collapse of a spherically symmetric scalar field. The algorithm uses the null initial value formulation of the Einstein-scalar equations, but...
Generating new magnetic universe solutions from old (1994)
Garfinkle, David, Melvin, M. A.
In this paper we apply the techniques which have been developed over the last few decades for generating nontrivially new solutions of the Einstein-Maxwell equations from seed solutions for simple...
Collapse of a Circular Loop of Cosmic String (1993)
Garfinkle, David, Duncan, G. Comer
We study the collapse of a circular loop of cosmic string. The gravitational field of the string is treated using the weak field approximation. The gravitational radiation from the loop is evaluated...
Results on exact solutions of low energy string theory (1992)
A family of solutions to low energy string theory is found. These solutions represent waves traveling along "extremal black strings"
Spherical topology in cardiac simulations
Puwal, Steffan, Roth, Bradley J., Garfinkle, David
Computational simulations of the electrodynamics of cardiac fibrillation yield a great deal of useful data and provide a framework for theoretical explanations of heart behavior. Extending the...