arXiv subjects
Publications and source records attributed to David Garfinkle.
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 Hamilton Conference Reports: 10th Capra Meeting on Radiation Reaction, by Carlos Sopuerta Quantum Gravity in the Southern Cone IV, by Rafael A. Porto
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: -Quasi-local energy, by Bjoern S. Schmekel -The current status of cosmic strings, by Patrick Peter -Gravitational waves from `mountains' on neutron stars, by Ian Jones Conference reports: -GR18/Amaldi 2007 in Sydney, by Jorge Pullin -Synergy in Singularities? by Don Marolf -Gravitation and the Cosmos, by Derek Fox and Parampreet Singh -NumRel meets PN, by Buonanno et al -SaulFest, by Greg Cook -3rd Gulf Coast Gravity Conference, by Vitor Cardoso
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 rotationally symmetric case) the Ricci flow for a ``critical'' initial geometry - one which is at the transition point between initial geometries (on $S^3$) whose volume-normalized Ricci flows develop a singular neck pinch, and other initial geometries whose volume normalized Ricci flows converge to a round sphere - evolves into a ``degenerate neck pinch.'' That is, we have seen in this earlier work that the Ricci flows for the critical geometries become locally cylindrical in a neighborhood of the initial pinching, and have the maximum amount of curvature at one or both of the poles. Here, we explore the behavior of these flows at the poles, and find strong support for the conjecture that the Bryant steady solitons accurately model this polar flow.
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 condition with time derivative along the normals to the slice ("BMn") as solutions of a mixed elliptic/hyperbolic differential equation on the slice. We show numerically that these steady states can be reached as end states from typical initial data with excision but can be reached with the puncture method only if the puncture is not numerically well resolved. During the evolution, BMn slicings often form gauge shocks. It may be that these are not seen in current 3D simulations only through lack of resolution, although we expect that they can be avoided with some care. Finally we point out that excision with BMn as currently implemented is ill-posed and therefore not expected to converge; this can be cured. In technical appendixes, we derive the equations of pure gauge systems on a fixed spacetime, and bring the BSSN/NOR equations into 3-dimensional tensor form suitable for multiple coordinate patches or spherical polar coordinates.
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 is developed, and numerical simulations are performed. The collapse produces regular, stationary black holes, as long as the aether coupling constants are not too large. For larger couplings a finite area singularity occurs. These results are shown to be consistent with the stationary solutions found previously.
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 Double Pulsar, by Michael Kramer - Theoretical Approaches to Cosmic Acceleration, by Mark Trodden Conference Reports: - Numerical Relativity-Data Analysis, by Patrick Brady - Note on Numerical Relativity-Data Analysis, by Peter Saulson - Unruh and Wald Fest, by Carsten Gundlach and David Garfinkle - Will Fest, by Eric Poisson - Brane-World Gravity, by Andrew Mennim - Gravity and Theoretical Physics, by Marco Cavaglia
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 Donald Marolf Quantum Gravity in the Americas III, by Jorge Pullin New Frontiers in Numerical Relativity, by Luciano Rezzolla Teaching General Relativity to Undergraduates, by Greg Comer Ninth Capra Meeting on Radiation Reaction, by Lior Burko
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 $Λ$CDM cosmology does.
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 analogy with the Aharonov-Bohm effect of quantum mechanics.
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.
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 general behavior of singularities in the presence of such matter. It is found that the singularity is spacelike and that as it is approached, the spacetime dynamics becomes local and non-oscillatory.
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 system. Well-posedness of the Cauchy problem follows from a standard theorem.
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 of singularities. It is found that the singularity is spacelike and that as it is approached, the spacetime dynamics becomes local and oscillatory.
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 initial data is essentially a thick domain wall connecting two regions of anti de Sitter space. The evolution results in no violation of cosmic censorship, but rather the formation of a small black hole.
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 what is known about these spikes.
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 essentially a thick domain wall connecting two regions of anti-deSitter space. The initial data has a free parameter that is the initial size of the wall. The simulation shows no violation of cosmic censorship, but rather the formation of a small black hole. The simulation described here is for a moderate wall size and leaves open the possibility that cosmic censorship might be violated for larger walls.
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 terms in the field equations dominate, and the singularity behaves locally like a homogeneous oscillatory spacetime.
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 of S^2 neck pinching, we find critical behavior at the threshold of singularity formation.