12th Eastern Gravity Meeting

main  lodging  announcements: 1st ; 2nd  participants  program  local info
All talks are 15 minutes plus 3 minutes of questions.
Sophia Maggelakis / Manuela Campanelli / John Whelan,
Welcome to RIT  Sophia Maggelakis, interim Dean, College of Science
Welcome from the CCRG  Manuela Campanelli, Director, Center for
Computational Relativity and Gravitation
Logistical Information  John Whelan, Chair, EGM 2009 Local
Organizing Committee
Jeff Winicour, University of Pittsburgh
The principle part of Einstein equations in the harmonic gauge consists of a constrained system of 10 coupled quasilinear space wave equations for the components of the spacetime metric. A strongly wellposed initialboundary value problem based upon a new formulation of constraintpreserving boundary conditions of the Sommerfeld type has recently been established for such systems. I will describe how these analytic results can be recast in a geometric form that provides a covariant interpretation of the boundary data. This serves as a first step toward applying these boundary conditions to other metric formulations of Einstein's equations.
Maria C. BabiucHamilton, Marshall University
Numerical relativity uses computational methods and supercomputers to solve Einstein's field equations for the binary black hole problem, in order to calculate the gravitational waveforms emitted. Most codes presently being applied to the binary black hole problem introduce an artificial outer boundary, and extract the waveform at an inner worldtube situated inside the outer boundary, in order to isolate the errors introduced by the boundary condition. The Cauchycharacteristic extraction (CCE) method offers means to avoid these errors altogether, by taking the data supplied by the Cauchy evolution on an inner worldtube and performing a characteristic evolution to future null infinity, where the waveform can be computed by geometric methods. Recently, we developed, tested and compared two new distinct methods: numerical and geometrical for improving the accuracy of extracting waveforms using characteristic evolution. In this talk we summarize the CCE approach and discuss the accuracy problem we found in the postprocessing phase, which reflects the intrinsic difficulty in extracting waveforms due to the delicate large number to small number cancellation of leading order terms in the metric. We propose two distinct ways in improving the accuracy that is needed for realistic astrophysical applications: by developing constraintpreserving boundary conditions at the inner extraction worldtube and by implementing a higher (4th) order finite difference approximation in the postprocessing phase of the waveform extraction. We expect our work to be a significant step towards the goal of delivering a CauchyCharacteristic patching computational module that will be available to the numerical relativity community.
Bruno C. Mundim, Rochester Institute of Technology
Detailed information concerning the general relativistic dynamics of compact binary systems relies on computer simulation involving the solution of very complicated systems of timedependent partial differential equations in three spatial dimensions. It is only over the past few years that reasonably accurate simulations of individual mergers has become possible. The complexity and cost of these calculations in part motivates our use of an approximation of general relativity, as well as our choice of a type of matter that is easier to model than a fluid. The approximation that is adopted places certain restrictions on the dynamical variables of general relativity (conformal flatness of the 3metric) and on the timeslicing of the spacetime (maximal slicing), and has been previously used in the modeling of neutron stars mergers. By studying a simplified, and more computationally tractable model within the context of the approximation, we hope to gain insight into the basic gravitational physics of compactobject interaction, as well as to eventually calibrate the fidelity of the approximation. This talk reports on numerical studies of binary boson stars within the context of this approximation, the conformally flat approximation, and discusses some results from initial explorations of the orbital dynamics of boson star binaries.
Hans Bantilan, Princeton University (student)
The AdS/CFT correspondence conjectures that a gauge theory admits a dual gravity description in a negatively curved spacetime. In particular, a heavy ion collision described by QCD has been conjectured as dual to a black hole collision in 5dimensional antide Sitter (AdS) space. BHBH collisions have received a lot of attention in the field of numerical relativity, in the context of gravitational waves generated in their inspiral phase and upon merger. By taking advantage of techniques in numerical relativity to simulate 5dimensional AdS, it is hoped that we can learn a bit more about heavyion physics, and perhaps more about the AdS/CFT correspondence in the process. I will describe steps that are being taken in this direction, first focusing on motivations, and then on preliminary simulations.
Tomas Liko, Pennsylvania State University
The onshell path integral for asymptotically flat Euclidean spacetimes in the firstorder formulation of general relativity is discussed. In particular, it is shown that the partition function can be derived without assuming the boundary to be isometrically embedded in flat space and without adding infinite counterterms to the boundary action. The resulting partition function reproduces the correct thermodynamic quantities for a number of solutions to the field equations.
Artur Tsobanjan, Penn State (student)
Canonical approaches to quantizing general relativity or symmetry reduced mini and midisuperspace cosmological models require a method for dealing with constraints representing diffeomorphism invariance. Exact procedures for Dirac's constraint quantization are typically difficult to implement. A technique for treating quantum constraints ``effectively'' is examined through the example of a relativistic particle in a Minkowski spacetime.
Gianluca Calcagni, Penn State
We describe some recent developments in Horava's theory of gravity. Inclusion of a scalar field under the detailed balance condition leads to problems which suggest the latter should be abandoned. General cosmological properties of the model, in vacuum and with matter, are also discussed.
Edward WilsonEwing, Pennsylvania State University (student)
We briefly introduce loop quantum cosmology and then show how Bianchi I spacetimes can be quantized in this framework. We construct the quantum Hamiltonian constraint, determine its action on a wavefunction for quantum spacetimes whose matter content is a massless scalar field and present the effective equations approximating the full dynamics. We also show that it is possible to project the full dynamics of the quantum Bianchi I state to an isotropic subspace wherein the resulting dynamics are identical to those found for quantum FriedmannRobertsonWalker spacetimes.
Jolyon Bloomfield, Cornell University (student)
An important part of understanding extradimensional models of our universe lies in extracting what the low energy implications are for our observable fourdimensional universe. We have obtained a general method for obtaining an effective fourdimensional action for a given braneworld model which accurately reproduces results obtained by other methods, but is scalable to a larger class of models. We discuss our method, its implications, and preliminary results we have obtained using it.
Abdul Hussein Mroue, Cornell University (student)
We present a first order formulation of the BSSN system that is evolved for a single black hole using the spectral code (SpEC) of the Caltech/Cornell collaboration.
Rob Owen, Cornell University
I present a method for defining and computing source multipole moments on dynamical black hole horizons, and numerical results using this method to demonstrate the ringdown of the remnant of a binary black hole merger to the Kerr geometry.
Frans Pretorius, Princeton University
It has been suggested that particle collisions at centerofmass energies above the Planck scale form back holes, which is the basis for claims that the LHC will produce black holes if the Planck is on the order of a TeV. Furthermore, at such energies it has been argued that the details of the internal structure of the particles is irrelevant in the collision process, with gravity dominating the interaction. This implies, for example, that black holes could be used as models of the particles to begin with. We will present results from simulations of high speed black hole and soliton collisions in general relativity, with the goal of finding evidence for or against these claims.
Yosef Zlochower, Rochester Institute of Technology
I will discuss a technique for determining the the algebraic classification of a numerically generated spacetimes resulting from a generic blackholebinary merger. Postmerger, the spacetime quickly approaches Petrov type II, and only approaches type D on much longer timescales. These techniques, in combination with techniques for evaluating acceleration and NUT parameters, allow us to begin to explore the validity of the ``nohair theorem'' for generic mergingblackhole spacetimes.
Hiroyuki Nakano, Rochester Institute of Technology
We discuss a two body system in the blackhole perturbation approach. This system consists of a Kerr (massive) black hole and a spinning point particle. Gravitational recoils of the merger are evaluated from the linear momentum loss.
Matthew Duez, Cornell University
The merger of a neutron star with a comparablemass black hole is a strong source of gravitational waves and a promising setup for generating a shortduration gamma ray burst. The merger may proceed quite differently depending on the mass ratio, black hole spin, and neutron star equation of state. In this talk, I present results of numerical simulations of black holeneutron star mergers with different black hole spins aligned with the orbital angular momentum. I review the special features of our code, which evolves the spacetime metric pseudospectrally on one grid and the neutron star fluid using finite volume techniques on a second grid. Black hole spin significantly affects the merger, leading to an increase the mass of the postmerger accretion disk.
Francois Foucart, Cornell University (student)
The inspiral and the merger of a neutron star and a black hole of a few solar masses is an important source of gravitational waves observable by groundbased detectors. And if such mergers can create hot and massive accretion disks, they could lead to the emission of shorthard gammaray bursts. However the evolution and the final state of these binaries are expected to be sensitive to the initial parameters, such as the mass ratio and the black hole spin, and to the unknown equation of state of the neutron star. The comparison of future experimental results with numerical simulations will give us new constraints on this nuclear equation of state. In this talk I will present numerical simulations of black holeneutron star binaries in which the fluid is modeled as a polytrope, and stars of different stiffness and compactness are considered. I will discuss the influence of these parameters on the disruption of the star, the formation of an accretion disk, and their observable consequences.
Carlos Lousto, Rochester Institute of Technology
We propose simple empirical formulae to describe the final remnant mass, spin, and recoil velocity from the merger of quasicircular blackhole binaries with arbitrary mass ratios and spins. Our formula is based on postNewtonian scaling with parameters chosen by a leastsquares fit of the available data from recent full numerical simulations and is relevant to statistical studies of Nbody simulations of galaxy cores and clusters, and the cosmological growth of supermassive black holes.
Geoffrey Lovelace, Cornell University
Research on extracting science from binaryblackhole simulations has often adopted a "scattering matrix" perspective: given the binary's initial parameters, what are the final hole's parameters and the emitted gravitational waveform? This talk focuses on a complementary approach: using binaryblackhole simulations to explore the nonlinear dynamics of curved spacetime. In particular, the LandauLifshitz pseudotensor is used to describe the density and flux of a binary's linear momentum. A simulation of a headon plunge, merger, and ringdown of a binary black hole with antiparallel spins is used to numerically explore the momentum flow between the holes and the surrounding spacetime. To investigate the gauge dependence of our results, we compare simulations in several different gauges, and we also compare our simulations with the Maxwelllike postNewtonian approximation.
Lawrence Kidder, Cornell University
We calibrate the effectiveonebody (EOB) model to an accurate numerical simulation of an equalmass, nonspinning binary blackhole coalescence produced by the CornellCaltech collaboration. These results improve and extend recent successful attempts aimed at providing gravitationalwave data analysts the best analytical EOB model capable of interpolating accurate numerical simulations.
David Merritt, Rochester Institute of Technology
Stars orbiting very close to the supermassive black hole at the center of the Milky Way will experience precession of their orbital planes induced by relativistic frame dragging and by the quadrupolar gravity of the hole, at levels that are potentially observable using adaptive optics on the next generation of large groundbased telescopes. Astrometric observations of the orbits of at least two such stars can in principle lead to a determination of the angular momentum vector of the black hole and its quadrupole moment, allowing a test of the general relativistic nohair theorems. We present the first relativistic Nbody simulations of stellar motions around the Milky Way black hole and evaluate the degree to which orbital precession would be influenced by Newtonian perturbations from other stars and from compact stellar remnants.
Parker Troischt, Hartwick College
Relativistic magnetohydrodynamics is important in a wide variety of astrophysical phenomena including: active galactic nuclei, pulsars, accreting black holes and gamma ray bursts. Fundamental to the study of any physical system is a study of its wave modes. We present a physically intuitive Lagrangian fluid formalism of relativistic MHD and apply it to study the propagation and interaction of wave modes in a black hole spacetime.
David Saroff, Rochester Institute of Technology (student)
Programs in Mathematica for calculating test particle orbits around spinning black holes will be presented. These programs run in PC's and are interactive. Strategy for accelerating PC's using graphics boards carrying GPU chips is discussed as a gentle route into GPU cluster computing for orbit calculations that include radiation reaction.
Marcelo Ponce, Rochester Institute of Technology (student)
In this presentation we will review the recently proposed mechanisms where gravitational waves are able to imprint electromagnetic signals in matter. In particular we will focus in the case where the scenario for such mechanism is an accretion disk around a supermassive black hole merger. Recently some works have suggested that gravitational waves emitted by the merger of two supermassives black holes would be enable to interact with an accretion disk, in such a way that through a viscous dissipation the matter will be enable to radiate electromagnetic waves. If such situation is possible, it could be a very important element to take into account for test and correlate other kind of observational surveys of gravitational waves.
Fabio Antonini, Rochester Institute of Technology (student)
The tidal breakup of binary star systems by the supermassive black hole (SMBH) in the center of the galaxy has been suggested as the source of both the observed sample of hypervelocity stars (HVS) in the halo of the galaxy and the Sstars that remain in tight orbits around Sgr A*. Here, we use a postNewtonian Nbody evolution code to study the dynamics of mainsequence binaries on highly elliptical bound orbits whose pericenters lie close to the SMBH, determining the properties of ejected and bound stars as well as collision products. Unlike previous studies, we follow binaries that remain bound for several revolutions around the SMBH, finding that in the case of relatively large pericenters the binaries undergo Kozai resonances which drive stellar collisions. The Kozai mechanism is only partially suppressed when postNewtonian terms are included in the integrations. Collisions and mergers of the binary elements are found to increase significantly for multiple orbits around the SMBH, while HVS are primarily produced during a binary's first passage.
Peter J. Zimmerman, Syracuse University (student)
We discuss the effect of residual eccentricity in searches for compact binary inspirals in LIGO data. LIGO currently uses circular postNewtonian waveforms as matched filters. For binaries that have evolved under typical mainsequence evolution, eccentricity will be radiated away by the time the gravitational waves enter the LIGO band, however it is possible that binary systems formed by direct capture may have nonzero eccentricities when their waves enter the LIGO band. To model the gravitationalwave signal generated by eccentric binaries, we use a postNewtonian quasiKeplerian parameterization proposed by Hinder et. al. The evolution of binary's orbital frequency and eccentricity are treated adiabatically at 2pN order in radiationreaction. The model also includes conservative postNewtonian terms which may influence the phase evolution of the binary. To understand the effects of the eccentricity, we calculate the overlaps between the eccentric signals and the SPA templates currently used by LIGO to search for gravitational waves.
Collin Capano, Syracuse University (student)
We report on the search for gravitational waves from coalescing compact binary systems with total mass from 235 solar masses in the LIGO Fifth Science run (S5) data and Virgo's Science Run 1 (VSR1). We describe the pipeline employed by the LSC/Virgo to search for such waveforms in LIGO/Virgo data including how we suppress false signals originating from instrumental noise, how we evaluate the search efficiency for systems which may include spinning component objects, and how we establish confidence in likely detection candidates. Finally, we describe Bayesian coalescence rate upper limit calculations as a function of mass of the binary system and for several canonical mass systems including mass distributions representing binary neutron stars, binary black holes, and black hole neutron star binaries.
Larne Pekowsky, Syracuse University (student)
Two important advances have occurred in recent years which have brought us closer to the goal of observing and interpreting gravitational waves from coalescing compact objects: the successful construction and operation of a worldwide network of groundbased gravitationalwave detectors and the impressive success of numerical relativity in successfully simulating the merger phase of Binary Black Hole (BBH) coalescence. The aim of the NINJA project is to study the sensitivity of gravitationalwave analysis pipelines to numerical simulations of waveforms and foster close collaboration between numerical relativists and data analysts. Over 75 numerical relativists and data analysis participated in the contribution of a simulated data set containing numerical waveforms, analysis of this data and interpreting the results of this analysis. We present an overview of the results of the NINJA project with emphasis on the results from the inspiral dataanalysis algorithms.
John T. Whelan, Rochester Institute of Technology
Crosscorrelation of gravitationalwave (GW) data streams is the standard technique to search for stochastic backgrounds, and has also been applied to searches for GW bursts. I describe the recent extension of this method to search for longlived quasiperiodic gravitational waves, taking into account features of the signal model.
Marc Favata, Kavli Institute for Theoretical Physics
The nonlinear memory effect discovered by Blanchet, Damour, and Christodoulou is a slowlygrowing, nonoscillatory contribution to the gravitationalwave amplitude. In an ideal gravitationalwave interferometer a gravitationalwave with memory causes a permanent displacement of the test masses that persists after the wave has passed. Surprisingly, the nonlinear memorywhich originates from the stressenergy tensor of the emitted gravitational wavesaffects the signal amplitude starting at leading (Newtonianquadrupole) order. Like gravitationalwave "tails", the nonlinear memory is "hereditary": its value at any given retarded time depends on the entire pasthistory of the source. For a variety of reasons, the nonlinear memory is not easily calculable with current numerical relativity (NR) simulations. I will discuss recent work involving the nonlinear memory, including some subset of the following: 1) computations of the memory contribution to the waveform polarizations to thirdpostNewtonian (PN) order for quasicircular binaries; 2) effectiveonebody (EOB) calculations of the memory from binary black hole mergers; 3) a hybrid PN/NR computation of the memory based on the Caltech/Cornell binary black hole merger simulations; 4) the effects of binary eccentricity on the memory signal; and 5) the potential for detecting the memory with ground and spacebased interferometers.
Sarah Vigeland, Massachusetts Institute of Technology (student)
Observations show the existence of many extremely compact, massive objects which are generally believed to be black holes. Precise observations have the potential to determine if these black hole candidates have the multipolar structure predicted by general relativity. Collins and Hughes proposed analyzing these systems by considering ``bumpy black holes'': objects that are almost, but not quite, black holes. In this paper we extend the work of Collins and Hughes. We describe how to define smooth perturbations that correspond to modifying in a prescribed way the multipolar structure of the black hole spacetime. We describe the effect of the bumps by describing how the frequencies of motion change using HamiltonJacobi techniques.
James Gilmore, Yale University (student)
Recently, a new method of calculating in the postNewtonian expansion has been introduced. As proposed by Goldberger and Rothstein, this approach employs the techniques of effective field theory, methods that have been in routine use in the particle physics community for many decades. Within this new framework, I will focus on gravitational bound states and discuss the recent calculation of the conservative second postNewtonian binary dynamics. For the conservative dynamics, the use of a metric parametrization based on a temporal KaluzaKlein decomposition is shown to have important calculational advantages, particularly when used at higher orders in the postNewtonian expansion. Additionally, progress we are making towards the calculation of the conservative third postNewtonian binary dynamics will be presented.
Andreas Ross, Yale University
This talk will describe the further development of the effective field theory NRGR as a tool to systematically calculate PN corrections in the radiation sector. The matching onto an effective theory describing the binary as a single worldline with multipole moments is accomplished by summing Feynman diagrams. Interesting effects arise when nonlinear interactions between the multipoles are included. We will present the calculation of the tail and the tailoftail effects where both infrared and ultraviolet divergences occur. While the infrared divergences exponentiate to a phase of the amplitude, the ultraviolet divergences need to be renormalized which leads to RG running of the mutlipole moments. We also resum the leading contributions of the tail effect to the power loss summing ladder diagrams.
Andrew Randono, Pennsylvania State University
I investigate the manner in which the internal spin angular momentum of a spinor field is encoded in the gravitational field at asymptotic infinity. The inclusion of internal spin requires us to reanalyze our notion of asymptotic flatness. In particular, the Poincar'{e} symmetry at asymptotic infinity must replaced by a spinenlarged Poincar'{e} symmetry. Likewise, the generators of the asymptotic symmetry group must be supplemented to account for the internal spin. In the Hamiltonian framework of first order EinsteinCartan gravity, the extra generator comes from the boundary term that must be added to the Gauss constraint in the asymptotically flat context. With the additional term, we establish the relations among the Noether charges of a Dirac field, the Komar integral, and the asymptotic ADMlike geometric integral. We show that by imposing mild restraints on the generating functionals of gauge transformations at asymptotic infinity, the phase space is rendered explicitly finite. Further demanding that the symmetries reduce to the spinenlarged Poincar'{e} group at asymptotic infinity imposes additional constraints on the allowed internal gauge transformations. We construct the energymomentum and the new total (spin+orbital) angular momentum boundary integrals that satisfy the appropriate algebra to be the generators of the spinenlarged Poincar'{e} symmetry.
J. Brian Pitts, University of Notre Dame
The problem of finding a covariant expression for the distribution and conservation of gravitational energymomentum dates to the 1910s. A suitably covariant infinitecomponent localization is displayed, reflecting Bergmann's realization that there are infinitely many gravitational energymomenta. Initially use is made of a flat background metric (or rather, all of them) or connection, because the desired gauge invariance properties are obvious. Partial gaugefixing then yields an appropriate covariant quantity without any background metric or connection; one version is the collection of pseudotensors of a given type, such as the Einstein pseudotensor, in _every_ coordinate system. This solution to the gauge covariance problem is easily adapted to any pseudotensorial expression (LandauLifshitz, Goldberg, Papapetrou or the like) or to any tensorial expression built with a background metric or connection. Thus the specific functional form can be chosen on technical grounds such as relating to Noether's theorem and yielding expected values of conserved quantities in certain contexts and then rendered covariant using the procedure described here. The application to angular momentum localization is straightforward. Traditional objections to pseudotensors are based largely on the false assumption that there is only one gravitational energy rather than infinitely many.
Joshua Faber, Rochester Institute of Technology
I will describe some preliminary efforts to study the evolution of circumbinary disks around merging and kicked black holes. I will go over some analytical estimates of various quantities, including some scaling laws rarely seen in relativity talks (the speed of light doesn't always equal 1!). SPH calculations of disks around the merged, kicked BH will be presented, showing the rapid heating and expansion of a welldefined accretion disk.
Munawar Karim, St. John Fisher College
In order to explain the anamolous expansion of the Universe, we posit a Universe filled with gravitational radiation. We derive its equation of state; we solve the Einstein equation. We get an exact solution. The solution gives us the evolution of a Universe filled with gravitational radiation. We fit the solution to the magnitude  redshift data. These are our results: current density is 0.4, current temperature of the cosmological background radiation is T=23K, k=1 (the Universe is open), transition redshift 0.77, current coordinate radius 20 billion light years, mass of Universe 10^54 kg  all of it is gravitational radiation. In the vicinity of the Galaxy the energy density per unit logarithmic frequency interval is 10^10 compared with 10^8 the upper bound set by observations of pulsar signals over 8 years.