Fourth Gulf Coast Gravity Meeting (GCGM4)

Usama al-Binni (
Black holes on branes with finite tension
Abstract: Black holes residing on a brane are expected to be observed at the LHC pointing to the existence of large extra dimensions. Signatures include the spectrum of Hawking radiation and quasi-normal modes through the detection of decay products. One important factor that is often neglected in calculations such as these is brane tension. We present the results of calculations that include brane tension for both quasi-normal frequencies and grey-body factors, and the expressions presented will be valid for any value of the tension of the brane (low as well as high).

James Alsup (
Bjorken flow from an AdS Schwarzschild black hole
Abstract: We consider a large black hole in asymptotically AdS spacetime of arbitrary dimension with a Minkowski boundary. By performing an appropriate slicing as we approach the boundary, we obtain via holographic renormalization a gauge theory fluid obeying Bjorken hydrodynamics in the limit of large longitudinal proper time. The metric we obtain reproduces to leading order the metric recently found as a direct solution of the Einstein equations in five dimensions. Our results are also in agreement with recent exact results in three dimensions.

Brett Bolen (
Solutions to typical quantum mechanics problems using the GUP
Abstract: The motivations for having a minimal length scale will be examined, then the talk will examine the effect of the GUP on various QM problems such as the SHO, the Hydrogen atom, and square wells.

Luca Bombelli (
Dynamics of causal sets
Abstract: After an introduction to the causal set approach to quantum gravity, I will first present a brief overview of the status of the main attempts at formulating a dynamical theory for causal sets, and then the results of recent work with Roman Sverdlov on expressing the action for general relativity with coupled matter fields in causal set terms.

Lior Burko (
Black-hole quasi-normal mode spectroscopy with LISA
Abstract: We present an improved estimate of the signal-to-noise ratio (SNR) from the ring-down phase of coalescing equal mass black hole binaries for the NASA/ESA space-borne interferometer LISA. The usual angle-averaged expressions of spin-weighted spheroidal harmonics, source parameters, and detector functions have been replaced by Monte-Carlo variables. For a given ``radiation efficiency" $\epsilon_{\rm rd}$, we use randomly generated ``radiation efficiency per polarization" $\epsilon^{+,\times}$ to estimate the non-angle-averaged, polarization- phase-dependent SNR for Schwarzschild and Kerr black holes. For fixed black hole spin parameter our SNR curve approaches the all-sky average curve in the large source number limit, but is different from it for finite number of sources. Allowing the black hole spins to vary randomly across the sky, the two curves are different also in the large numbers limit.

Marco Cavaglià (
Past, present and future of LIGO
Abstract: LIGO completed its fifth science run at design sensitivity in October 2007. While the instruments are being prepared for the next phase, Enhanced and Advanced LIGO, data analysis is well under progress. LIGO's recent study of GRB070201 gave an important contribution towards the understanding of gamma-ray bursts. In this talk, I will briefly discuss the status of the experiment, future plans, and the work being done by more than 500 scientists to achieve the first-ever detection of a gravitational-wave signal.

Hristu Culetu (
On the Doran - Lobo - Crawford time dependent spacetime
Abstract: On the grounds of an idea of Doran et al., we propose a new version of the geometry inside a black hole. The spacetime is a solution of Einstein's equations with an anisotropic fluid stress tensor as source of gravity. The energy density of the fluid is proportional to $1/t^{2}$, as in many dark energy models, but the Brown - York quasilocal energy of the black hole equals its mass $m$. When the sign of the angular coefficients from the line element is changed, the geometry is a time dependent solution of Einstein's equations in vacuum.

Steven Detweiler (
Regularization of the gravitational field for self-force problems in curved spacetime
Abstract: We propose an approach for the numerical calculation of self-force, energy flux and waveform arising from a small black hole orbiting a much larger one. This approach regularizes the field by analytically identifying and removing the singular part of the retarded field yielding a finite, differentiable remainder from which the self-force, and energy flux and wave form are easily calculated. This regular remainder solves a wave equation which enjoys the benefit of having a non-singular source, and its solution completely avoids the calculation of the singular retarded field along with the attendant difficulties associated with numerically modeling a delta function source.

Peter Diener (
Abstract: The moving puncture approach has revolutionized our ability to perform black hole evolution and has led to an amazing amount of physics results. One major question is whether the method is limited to puncture initial data. There are other types of data available, such as the Meudon and the Cook-Pfeiffer initial data, which are not defined in the interior of the black holes. We have invented a way of filling in the interior of a black hole with a smooth solution that allows us to evolve these types of initial data with the standard moving puncture techniques. We call it "turduckening", after the southern dish "turducken" where a turkey is stuffed with a duck stuffed with a chicken.

Segio Fabi (
Zero point energy on extra dimension: Noncommutative torus
Abstract: We calculate the zero point energy density experienced by observers on M^4 due to a massless scalar field defined throughout M^4 x T^2_F, where T^2_F are fuzzy extra dimensions. Using the Green's function approach we calculate the energy density for the commutative torus and the fuzzy torus. We calculate then the energy density for the fuzzy torus using the Hamiltonian approach. Agreement is shown between Green's function and Hamiltonian approaches.

Jun-Qi Guo (
Data Quality vetoes for high-mass compact binary coalescences in LIGO's 5th science run
Abstract: In the search for gravitational waves, environmental and instrumental disturbances produce transient non-Gaussian noise in the data. The vetoing of these bad stretches of data is an essential step of the detection pipeline. First, data quality flags for the triggers which are generated by the transient noise are identified. The flagged times are then refined and categorized to produce veto windows. We show a few examples of noise transients and how the data can be cleaned by this procedure.

Oleg Korobkin (
Solving Einstein's constraints on multi-block triangulations using finite elements
Abstract: We present an approach for solving Einstein's constraint equations on three-dimensional multi-block domains using finite element methods. We use quadratic Lagrange elements on semi-structured simplicial meshes, obtained by triangulation of multi-block grids. In the case of uniform refinement the scheme is superconvergent at most mesh vertices, due to local symmetry of the finite element basis with respect to local spatial inversions. We show that in the superconvergent case subsequent unstructured mesh refinements do not improve the quality of our initial data. As proof of concept that this approach is feasible for generating multi-block initial data in three dimensions, after constructing the Brill wave initial data we evolve them in time using a high order finite-differencing multi-block approach and extract the gravitational waves from the numerical solution.

Tyler Landis (
Multi-patch general relativistic magnetohydrodynamics
Abstract: Many astrophysical systems with strong relativistic components have near spherical or axisymmetric geometries. In order to achieve accurate results, it is best to simulate these systems on grids that are spherical or cylindrical. These grids, however, possess coordinate singularities that make fully relativistic models difficult to use. By employing a system of multiple patches, Zink, Schnetter, Tiglio, 2007 were able to demonstrate how to solve fixed-background hydrodynamical systems on near spherical coordinates without coordinate singularities. In this talk, I will describe the status of the code and present the further extensions of the code currently being implemented and tested as well as possible applications of the code including black hole accretion disks.

Frank Loeffler (
Numerical simulations of binary neutron star - black hole systems
Abstract: I will give a short overview on our numerical work on the subject of binary neutron star - black hole mergers with the focus on the methods used for the initial data.

Pedro Marronetti (
High-spin binary black hole mergers
Abstract: We study identical mass black hole binaries with spins perpendicular to the binary's orbital plane. These binaries have individual spins ranging from $s/m^2=-0.90$ to $0.90$, ($s_1 = s_2$ in all cases) which is near the limit possible with standard Bowen-York puncture initial data. The extreme cases correspond to the largest initial spin simulations to date. Our results expand the parameter space covered by Rezzolla {\it et al}. and, when combining both data sets, we obtain estimations for the minimum and maximum values for the intrinsic angular momenta of the remnant of binary black hole mergers of $J/M^2=0.341(4)$ and $0.951(4)$ respectively.

Brian Mazur (
High-velocity cloud interactions with the galactic halo
Abstract: Correlations are sought in both the observed X-ray and H-alpha emission seen in the interaction of the high-velocity clouds and the Galactic halo. Several methods of heating are proposed, such as shock heating, however I shall address the heating caused by the X-ray flux into the cloud.

Wolfgang Rindler (
The contribution of lambda to the bending of light
Abstract: In spite of many assertions in the literature up to this year that, wheras Lambda in principle affects the advance of the perihelia, it does not affect the bending of light, we show that indeed it does affect the bending of light. Like all Lambda effects, this one too is significant only at the cosmological scale. But then it must enter the lensing calculations.

Arunava Roy (
Discriminating supersymmetry and black holes at the Large Hadron Collider
Abstract: We show how to differentiate the minimal supersymmetric extension of the standard model from black hole events at the Large Hadron Collider. Black holes are simulated with the CATFISH generator. Supersymmetry simulations use a combination of PYTHIA and ISAJET. Our study, based on event shape variables, visible and missing momenta, and analysis of dilepton events, demonstrates that supersymmetry and black hole events at the LHC can be easily discriminated.

Fabio Scardigli (
Glimpses on the micro black hole Planck phase
Abstract: Mass thresholds and lifetims of micro black holes are computed using different generalized uncertainty principles. Results are compared with previous analog approaches.

Allen Stern (
Discrete spectra from noncommutative gravity

Myungkee Sung (
Optimal linear filter technique for detection of gravitational waves in the LIGO experiment
Abstract: The Laser Interferometer Gravitational-wave Observatory (LIGO) experiment is designed for the detection of gravitational waves. The optimal linear filter method, which is the direct application of the classical signal processes, is developed to search burst type gravitational waves. Hardware injection, which is used to simulate gravitational waves added into the data during the science runs, is a very important technique to find out how the detectors would respond to the signal waveforms from the gravitational wave sources. This presentation will discuss how hardware injections are performed in LIGO, and the optimal linear filter method will be demonstrated how to find the gravitational wave signal from the LIGO data by using hardware injection data.

Ian Vega (
Field regularization for self-force problems
Abstract: Motivated by the need to produce accurate waveforms for LISA capture sources, efforts have been made towards modeling the dynamics of inspiraling stellar-mass compact objects onto supermassive black holes. The small mass ratio in such systems make them naturally amenable to the tools of perturbation theory, in which the dynamics of the binary is first mapped onto that of a point mass moving in a black hole spacetime. Central to this approach is the calculation of a so-called self-force, which accounts for effects of the interaction between the point mass and its own field. In this talk, I shall spell out some of the challenges that remain in this subject, and then outline our approach to ameliorating them. I shall also discuss recent results of an implementation of our prescription to a scalar charge in a circular orbit around a Schwarzschild black hole.

Gerrit Verschuur (
On the relation between WMAP small-scale structure and galactic interstellar hydrogen features
Abstract: Associations between small-scale structure observed by the WMAP and similar features found in the distribution of interstellar neutral hydrogen have been discovered. Several hundred such associations have already been noted. It will be argued that these are not due to chance. We will illustrate the talk by showing some of the most dramatic cases, two of which also show associated soft X-ray emission. If it is nevertheless argued that all these associations are due to chance, one must ask whether we understand interstellar physics so well that they can be ignored in order to allow us to draw far-reaching cosmological conclusions from the WMAP data.

Ram Gopal Vishwakarma (
Einstein's gravity under pressure
Abstract: According to the general theory of relativity, not only the energy density but pressure also gravitates. This is regarded as a purely relativistic effect resulting from the covariant character of the theory and implies that in the presence of a positive pressure, a perfect fluid seems to carry additional energy density, though without any apparent source, hence defying the principle of conservation of energy and posing paradoxes. We show that this erroneous situation is not a consequence of general relativity or gravitation, but it also arises in Newtonian theory. It appears that the origin of the trouble lies in our erroneous belief that pressure is a scalar quantity, which becomes equivalent to assuming that the fluid carries an additional amount of energy density (which though does not really exist!). It is this spurious energy density which is the cause of the paradoxes mentioned above. Though the pressure in relativity is realized as components of a second-rank tensor in general, however in the absence of the shearing tangential stresses, the tensor leads to a diagonal form with the diagonal terms identical leaving the pressure as a scalar. Hence, although the paradox disappears from the Newtonian theory as soon as we realize the pressure as a vector quantity, the (nontrivial) situation in relativity requires to reformulate the energy-stress tensor in this light and leaves the predictions of the theory suspect which aredrawn in the presence of a non- negligible pressure term.

Paul Walter (
Status of openGR
Abstract: Supercomputers such as Ranger, consisting of over 60,000 processors, help make this an exciting time for numerical relativity. openGR provides an open framework for doing large general relativistic simulations. I will discuss the current status of openGR including matters of scaling and convergence tests. openGR was constructed for simulating the mergers of binary black holes, so I will discuss the progress towards that end.

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