arXiv subjects

Tehani K. Finch

Publications and source records attributed to Tehani K. Finch.

5 recordsLinked to original sources

arXiv2014

Coordinate families for the Schwarzschild geometry based on radial timelike geodesics

We explore the connections between various coordinate systems associated with observers moving inwardly along radial geodesics in the Schwarzschild geometry. Painlevé-Gullstrand (PG) time is adapted to freely falling observers dropped from rest from infinity; Lake-Martel-Poisson (LMP) time coordinates are adapted to observers who start at infinity with non-zero initial inward velocity; Gautreau-Hoffmann (GH) time coordinates are adapted to observers dropped from rest from a finite distance from the black hole horizon. We construct from these an LMP family and a proper-time family of time coordinates, the intersection of which is PG time. We demonstrate that these coordinate families are distinct, but related, one-parameter generalizations of PG time, and show linkage to Lemaître coordinates as well.

gr-qc↗

arXiv2013

Painlevé-Gullstrand-type coordinates for the five-dimensional Myers-Perry black hole

The Painleve-Gullstrand coordinates provide a convenient framework for presenting the Schwarzschild geometry because of their flat constant-time hypersurfaces, and the fact that they are free of coordinate singularities outside r=0. Generalizations of Painleve-Gullstrand coordinates suitable for the Kerr geometry have been presented by Doran and Natario. These coordinate systems feature a time coordinate identical to the proper time of zero-angular-momentum observers that are dropped from infinity. Here, the methods of Doran and Natario are extended to the five-dimensional rotating black hole found by Myers and Perry. The result is a new formulation of the Myers-Perry metric. The properties and physical significance of these new coordinates are discussed.

gr-qc↗

arXiv2011

Global Causal Structure of a Transient Black Object

A singularity-free and spherically symmetric transient black object whose center remains always timelike, yet directly manifests a trapped region, has been constructed and numerically implemented. The exterior geometry is shown to be similar to that of a long-lived transient black hole, with a few subtle differences. The large-scale global structure of the geometry is examined through the construction of a conformal diagram, which exhibits no event horizon and bears resemblance to that of a Minkowski spacetime. Since there is no singularity within the geometry, the evolution of the exchange of information between timelike observers, including those that fall through the trapped region, can be directly explored. The dynamics of generic "standard" communications, as well as entangled communications, is exhibited through both t-versus-r and conformal spacetime diagrams.

gr-qc↗

arXiv2009

Three-Charge Supertubes in a Rotating Black Hole Background

The low velocity scattering of a D0-F1 supertube in the background of a BMPV black hole has been investigated in the moduli space approximation by Marolf and Virmani. Here we extend the analysis to the case of the D0-D4-F1 supertube of Bena and Kraus. We find that, similarly to the two-charge case, there is a critical value of the supertube circumferential angular momentum; above this value an adiabatic merger with the black hole cannot occur. By reconsidering the calculation of supertube angular momentum in the transverse direction, correspondence between the worldvolume and supergravity descriptions is established. We also examine dynamical mergers and discuss their implications.

hep-th↗

arXiv2002

Analytic expressions for mean magnification by a quadrupole gravitational lens

We derive an analytic expression for the mean magnification due to strong gravitational lensing, using a simple lens model, a singular isothermal sphere embedded in an external shear field. We compute separate expressions for 2-image and 4-image lensing. For 4-image lensing, the mean magnification takes a particularly simple form: _4 = 3.6/(gamma*(1-gamma^2)), where gamma is the external shear. We compare our analytic results to a numerical evaluation of the full magnification distribution. The results can be used to understand the magnification bias that favors the discovery of four-image systems over two-image systems in flux-limited lens surveys.

astro-ph↗