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David Garfinkle

Publications and source records attributed to David Garfinkle.

At least 91 records · Page 5Linked to original sources
arXiv2011

Matters of Gravity, The Newsletter of the Topical Group on Gravitation of the American Physical Society, Volume 38, Fall 2011

GGR News: New version of LISA, by Karsten Danzmann We hear that, by David Garfinkle Research Briefs: Finally, results from Gravity Probe B, by Clifford M. Will Discovery of the highest mass neutron star, by Wynn C.G. Ho Conference reports: Numerical relativity beyond astrophysics, by Carsten Gundlac Cold materials, hot nuclei and black holes, by Vijay Balasubramanian Benasque workshop on gravity, by Oscar J.C. Dias

gr-qc↗
arXiv2011

A positive energy theorem for Einstein-aether and Hořava gravity

Energy positivity is established for a class of solutions to Einstein-aether theory and the IR limit of Hořava gravity within a certain range of coupling parameters. The class consists of solutions where the aether 4-vector is divergence free on a spacelike surface to which it is orthogonal (which implies that the surface is maximal). In particular, this result holds for spherically symmetric solutions at a moment of time symmetry.

gr-qc↗
arXiv2011

How extreme are extreme black holes?

We examine the properties of nearly extremal black holes produced by gravitational collapse. It is shown that an observer who crosses the black hole horizon at late times rapidly encounters a singularity.

gr-qc↗
arXiv2011

Non-Stationary Dark Energy Around a Black Hole

Numerical simulations of the accretion of test scalar fields with non-standard kinetic terms (of the k-essence type) onto a Schwarzschild black hole are performed. We find a full dynamical solution for the spherical accretion of a Dirac-Born-Infeld type scalar field. The simulations show that the accretion eventually settles down to a well known stationary solution. This particular analytical steady state solution maintains two separate horizons. The standard horizon is for the usual particles propagating with the limiting speed of light, while the other sonic horizon is for the k-essence perturbations propagating with the speed of sound around this accreting background. For the case where the k-essence perturbations propagate superluminally, we show that one can send signals from within a black hole during the approach to the stationary solution. We also find that a ghost condensate model settles down to a stationary solution during the accretion process.

hep-th↗
arXiv2011

Gravitational collapse of k-essence

We perform numerical simulations of the gravitational collapse of a k-essence scalar field. When the field is sufficiently strongly gravitating, a black hole forms. However, the black hole has two horizons: a light horizon (the ordinary black hole horizon) and a sound horizon that traps k-essence. In certain cases the k-essence signals can travel faster than light and the sound horizon is inside the light horizon. Under those circumstances, k-essence signals can escape from the black hole. Eventually, the two horizons merge and the k-essence signals can no longer escape.

gr-qc↗
arXiv2010

Examining gravitational collapse with test scalar fields

Numerical simulations are performed of a test scalar field in a spacetime undergoing gravitational collapse. The behavior of the scalar field near the singularity is examined and implications for generic singularities are discussed. In particular, our example is the first confirmation of the BKL conjecture for an asymptotically flat spacetime.

gr-qc↗
arXiv2010

Killing Tensors and Symmetries

A new method is presented for finding Killing tensors in spacetimes with symmetries. The method is used to find all the Killing tensors of Melvin's magnetic universe and the Schwarzschild vacuum. We show that they are all trivial. The method requires less computation than solving the full Killing tensor equations directly, and it can be used even when the spacetime is not algebraically special.

gr-qc↗
arXiv2009

Spikes in the Mixmaster regime of G_2 cosmologies

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 non-local where spikes occur. Higher order spike transitions are observed to split into separate first order spike transitions.

gr-qc↗
arXiv2009

Matters of Gravity, The Newsletter of the Topical Group on Gravitation of the American Physical Society, Volume 34, Fall 2009

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 Reports: AbhayFest, by Chris Beetle Eastern Gravity Meeting, by Jeff Winicour Benasque Workshop on Gravity, by Roberto Emparan and Veronika Hubeny Workshop on the Fluid-Gravity Correspondence, by Mukund Rangamani

gr-qc↗
arXiv2009

The motion of galaxy clusters in inhomogeneous cosmologies

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 clusters with respect to the cosmic microwave background. Those velocities can be measured using the kinematic Sunyaev-Zeldovich effect. This paper presents a calculation of galaxy cluster velocities as a function of redshift for such a model.

gr-qc↗
arXiv2009

The Parallelometer: a mechanical device to study curvature

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 and to study Berry phase shift when it is carried along a loop on the surface. Its connection to the Foucault pendulum is discussed. The experimental results can be successfully compared with the theoretical expectations. The experiment is inexpensive and conceptually easy to perform and understand for a beginner.

gr-qc↗
arXiv2008

Evolution to a smooth universe in an ekpyrotic contracting phase with w > 1

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, we explore how robust and powerful the ekpyrotic smoothing mechanism is by beginning with highly inhomogeneous and anisotropic initial conditions and numerically solving for the subsequent evolution of the universe. Our studies, based on a universe with gravity plus a scalar field with a negative exponential potential, show that some regions become homogeneous and isotropic while others exhibit inhomogeneous and anisotropic behavior in which the scalar field behaves like a fluid with w=1. We find that the ekpyrotic smoothing mechanism is robust in the sense that the ratio of the proper volume of the smooth to non-smooth region grows exponentially fast along time slices of constant mean curvature.

hep-th↗