# Theory Meets Data Analysis at Comparable and Extreme Mass Ratios

Conference Date:
Sunday, June 20, 2010 (All day) to Saturday, June 26, 2010 (All day)
Scientific Areas:
Strong Gravity

Searches for gravitational waves from coalescing compact binary systems rely on concrete knowledge of the waveform to achieve maximum sensitivity to these sources. With a network of earth-based detectors currently acquiring data at design sensitivity and LISA's future at a critical stage, the theoretical understanding of these systems and its impact on data analysis efforts is one of the most important activities in current gravity research. This conference will bring together researchers working in theoretical and data analysis efforts to further foster interactions between the different communities involved to exploit theoretical models in the data analysis enterprise. Additionally it will serve as a catalyst for future collaborations and developments among researchers working in numerical relativity and extreme-mass ratio fronts.

Parameswaran Ajith, California Institute of Technology

Leor Barack, Universtiy of Southampton

Michael Boyle, Cornell University

Avery Brodderick, CITA

Zachariah Etienne, University of Illinois at Urbana-Champaign

Abraham Harte, University of Chicago

Alexandre Le Tiec, Institut d'Astrophysique de Paris

Sean McWilliams, NASA-Goddard Space Flight Center

Craig Robinson, Cardiff University

Alberto Vecchio, University of Birmingham

Ian Vega, University of Guelph

Sam Waldman, Massachusets Institute of Technology

Invited speaker abstracts:

Parameswaran Ajith, Caltech

Interfacing numerical- and analytical relativity for gravitational-wave astronomy: Status and prospects

Recent progress in numerical- and analytical relativity enables us to construct analytical waveform templates coherently describing the inspiral, merger and ring down of coalescing black-hole binaries. Such waveform templates not only improve the sensitivity of the searches for gravitational waves from high-mass binaries significantly, but also the accuracy of the parameter estimation. This talk summarizes the status and prospects of different approaches of the modeling of gravitational waveform from binary black holes calibrated to numerical-relativity simulations.

Avery Brodderick, CITA

The Hairstyles of Compact Objects

While gravitational waves offer a new, and in many ways clean, view of compact objects, most of what we presently know about these has been obtained by careful study of their messy interactions with surrounding material.  I will summarize what we know about a variety of potential gravitational wave sources, how this astrophysical hair has helped to illuminate some of the same questions gravitational wave observations promise to address, and how future observations may begin to relate the gravitational and electromagnetic properties of compact objects.

Zachariah Etienne, University of Illinois at Urbana-Champaign

Fully General Relativistic Simulations of Black Hole-Neutron Star Mergers: A Current Overview

Black hole-neutron star binary (BHNS) mergers are likely sources for detectable gravitational radiation and candidate engines for short-hard gamma-ray bursts.  However, accurate modeling of these mergers requires fully general relativistic simulations, incorporating both relativistic hydrodynamics for the matter and Einstein's field equations for the (strong) gravitational fields.  I will review techniques and results from recent fully general relativistic BHNS merger simulations.  These simulations examine the effects of the BH:NS mass ratio, BH spin, and NS equation of state, focusing on both the gravitational waveforms and remnant disk.

Scott Hughes, Massachusetts Institute of Technology

Probing the physical and astrophysical nature of black holes with gravitational waves

Black holes play a central role in astrophysics and in physics more generally.  Candidate black holes are nearly ubiquitous in nature.  They are found in the cores of nearly all galaxies, and appear to have resided there since the earliest cosmic times.  They are also found throughout the galactic disk as companions to massive stars.  Though these objects are almost certainly black holes, their properties are not very well constrained.  We know their masses (often with errors that are factors of a few), and we know that they are dense.  In only a handful of cases do we have information about their spins.  Gravitational-wave measurements will enable us to rectify this situation.  Focusing largely on measurements with the planned space-based detector LISA, I will describe how gravitational-wave measurements will allow us to measure both the masses and spins of black holes with percent-level accuracy even to high redshift, allowing us to track their growth and evolution over cosmic time.  I will also describe how a special class of sources will allow us to measure the multipolar structure of candidate black hole spacetimes.  This will make it possible to test the no-hair theorem, and thereby to test the hypothesis that black hole candidates are in fact black holes are described by general relativity.

Sean McWilliams, NASA Goddard Space Flight Center

The Status of Black Hole Binary Simulations

The initial gold rush of exploration into new regions of parameter space has slowed significantly. While our ability to simulate larger spins and more extreme mass ratios has continued to improve, much of the recent progress in numerical relativity has centered on improvements in methodology, in condensing and interpreting an ever-growing body of numerical results, and in incorporating matter into the numerical simulations. In this review, I will summarize the recent progress in this field, focusing on novel results in the simulation of black hole binaries, with some discussion of novel applications of those results to data analysis.

Modelling waveforms from binary neutron stars

The familiar post-Newtonian inspiral description of a binary neutron star system is sufficient for detection in current instruments. However, as we consider making astrophysical measurements using advanced detectors, the effects of matter and strong gravity on gravitational wave signals may become significant. I will review recent work modelling the waveforms produced by the inspiral and coalescence of binary neutron stars. In the mid-to-late inspiral this includes modifications to the post-Newtonian waveform models from tidal deformations. In the late inspiral and coalescence, numerical simulations are exploring a range of masses, mass ratios, equations of state, and magnetic fields. In some circumstances a hypermassive remnant produces significant additional signal after the merger. Numerical simulation results also link neutron-star merger to potential counterpart signals.

Sam Waldman, Massachusets Institute of Technology

Gravitational Wave Detection:  Past, Present and Future

Direct detection of gravitational wave stands at a cross roads;  the first generation of interferometric  detectors will soon be decommissioned and the second generation projects are underway.   In this talk, I will describe the Initial LIGO and VIRGO generation of instruments, the techniques required to achieve a strain sensitivity of 3 x 10^{-23}  and an NS / NS inspiral range of 15 Mpc.   I'll follow with a description of the Advanced detectors and the differences that should improve the sensitivity by a factor of ten.  Finally,  I will describe projects from radio and microwave astronomy to measure gravitational waves using pulsar timing and the CMB B-mode polarization.

Contributed Abstracts:

Enrico Barausse, University of Maryland

Understanding spinning black-hole binaries: a new effective-one-body model

The dynamics of black-hole binaries is a very complex problem which has been solved only very recently through time-expensive numerical-relativity calculations. In spite of this mathematical complexity many results of these calculations can be accurately reproduced with phenomenological approaches based on test particles combined with Post-Newtonian theory and black-hole perturbation theory. In this talk I will focus on effective-one-body models, which have proved a useful and fast tool to accurately reproduce numerical-relativity waveforms. In particular I will present a novel, self-consistent effective-one-body model for spinning black-hole binaries, and show that this model does not suffer from the shortcomings of the existing models which have been put forward in the literature.

Thilina Dayanga, Washington State University Pullman

Comparing the performances of coherent and coincident network searches forbinary black hole mergers

A coherent multi-site search is expected to be more powerful than itscoincident counterpart in discriminating gravitational wave (GW) signals fromthe noise background. This is because the former tests the consistency of thesignals' amplitudes phases and time-delays across the sites with those expected from a real GW source. However the coherent statistic that is optimalin Gaussian noise is not guaranteed to perform as well in real data which arenon-Gaussian. Here we introduce an alternative coherent statistic for searchingcompact binary coalescence (CBC) signals that includes chi-square andnull-stream discriminators for non-Gaussian features in the data. Thisstatistic has been found to perform better than coincident statistics exploredin real data. This alternative coherent statistic is being used in ongoinginspiral-merger-ringdown searches in LIGO-Virgo data and is expected to beuseful in bridging the performance gap between the coincident CBC searchpipeline and the coherent burst search pipeline for detecting signalshigh-mass CBCs especially for systems with total-mass tending toward ahundred solar masses that have only a few signal cycles in band. We planto use this statistics in future NINJA analysis.

Steve Drasco, AEI Caltech

Generic spectral kludge

I have been working on a project with Curt Cutler in which among other things we have been calculating Fisher-matrix estimates for LISA's ability to measure the parameters that characterize EMRI waveforms.  Similar calculations have been done before but only for the Barack and Cutler waveforms.  Those waveforms are currently the workhorses for EMRI data analysis investigations.  They are very fast and relatively easy to implement but they are not especially realistic.  Our project uses a spectral representation more realistic waveforms first used by Babak et al in 2007 where they were shown to be good approximations of Teukolsky-waveforms even on timescales where radiation reaction is important.  While these improved waveforms are more accurate than Barack and Cutler waveforms and are almost certainly still affordable" from a data analysis perspective very little is known about what exactly would be gained or lost by their use as templates in real searches.  I will describe interesting details and advantages of our spectral representation of these waveforms will report on our parameter estimation results and will outline what we can expect to learn from them in the near future.

Stephen Fairhurst, Cardiff University

Coherently searching for spinning compact binary coalescences

In this talk we present the motivation behind our implementation of and results from a coherent search for spinning compact binary coalescences. Our method uses the Physical template family of waveforms which describe binaries where only one of the objects has spin.  In addition we discuss the possibility of extending thissearch to incorporate template waveforms for precessing black hole mergers derived from numerical relativity.

Automating the post-Newtonian expansion on a computer

With several ground-based gravitational wave interferometers operating at design sensitivity the need for high-order post-Newtonian (PN) calculations of potentials waveforms etc. especially including spin effects has grown significantly over the last several years. Not only are these calculations necessary for precisely estimating the parameters of detected gravitational wave sources but they are also useful for providing more accurate models of binary evolutions in for example the effective one-body program and for computing the PN contributions to self-force effects in the extreme mass ratio limit. Since these calculations become more demanding to carry out at higher PN orders it is necessary to utilize symbolic computer algebra programs (such as Mathematica). Our aim is to automate PN calculations (of potentials power loss etc.) on the computer using the effective field theory (EFT) approach of Goldberger and Rothstein which is itself a systematic and algorithmic method for computing in the PN approximation. The EFT approach lends itself to automation through definite power counting rules that identify precisely those interactions appearing at a given PN order through Feynman rules and diagrams that provide an elegant way to side-step the need to explicitly solve the wave equation for metric perturbations (unlike in traditional methods) through working at the level of the action (a scalar) instead of equations of motion etc. We discuss our progress in automating these calculations on a computer using the EFT approach.

Abraham Harte, University of Chicago

Spin-induced bobbing effects in relativistic systems

Recent numerical simulations of spinning binary black holes have found that the orbital plane tends to bob up and down in phase with the orbit. It will be shown that similar effects occur in nearly all relativistic systems. The reasons for this are essentially kinematic and appear unrelated to those leading to the final "kicks" observed after merger. Simple examples are provided for binary systems bound together by gravitational electromagnetic and mechanical forces.

Ilya Mandel, Northwestern University

Bayesian Inference on Numerical Injections

We describe a Markov-Chain Monte-Carlo technique to study the source parameters of gravitational-wave signals from the inspirals of stellar-mass compact binaries detected with ground-based detectors such as LIGO and Virgo. We can apply this technique to both spinning and non-spinning waveforms and we use a variety of tools like parallel tempering to improve the sampling efficiency of the algorithm in a multi-dimensional parameter space.  We describe new developments in model-selection techniques for distinguishing between alternative signal models.  We present preliminary results from the application of these techniques to data sets containing injections of numerical-relativity waveforms into simulated Gaussian detector noise. We study the source parameters of signals from the inspirals of stellar-mass compact binaries detected with ground-based gravitational-wave detectors such as LIGO and Virgo. We use automatic adaptation of the step size and take into account the correlations  between parameters to efficiently probe the parameter space while keeping the algorithm suitable for a wide range of signals. We shall discuss the  performance of the MCMC algorithm and the typical measurement accuracy of the source parameters as a function of the binary parameters and the number of detectors in the network. We will show that despite the lower positional accuracy compared to other astronomical observations an association of a gravitational-wave event with e.g. an electromagnetic detection is possible with three or even two 4-km-size interferometers.

Hiroyuki Nakano, Rochester Institute of Technology

Perturbative effects of spinning black holes with applications to full numerical relativity results

We present a second order perturbative formalism that includeperturbative spin effects and apply it to the computation of recoil velocites of merging binary black holes and to the computation of waveforms from small mass ratio binaries.

Frank Ohme, Albert Einstein Institute

Hybrid waveforms for binary black holes with aligned spins: Matching errors and a phenomenological model in the frequency domain

We present a new construction of phenomenological templates for non-precessing spinning black hole binaries. This approach utilizes a frequency domain matching of post-Newtonian inspiral waveforms with numerical relativity based binary black hole coalescence waveforms.  We quantify the various possible sources of systematic errors that could arise in matching post-Newtonian and numerical relativity waveforms and we use a matching criteria based on minimizing these errors.  An analytical formula for the dominant mode of the gravitational radiation of non-precessing black-hole binaries is presented that captures the phenomenology of the hybrid waveforms. Its implementation in the current searches for gravitational waves should allow cross-checks of other inspiral-merger-ringdown waveform families as well as an improvement of the reach of the detection algorithms.

Christian Ott, TAPIR Caltech

Gravitational Waves from Core-Collapse Supernovae

We present a short overview on the current state of core-collapse supernova modeling and the set of processes expected to emit gravitational waves in a core collapse event. We go on to show new results from 3D GR simulations focusing on failing black-hole forming supernovae and present the gravitational wave signature of such events.

Carlos Palenzuela, CITA

Binary black hole collision in a force-free environment

In this work we investigate the electromagnetic radiation induced by a binary black hole merger when they are surrounded by a force-free environment (i.e. plasma with inertia terms negligible compared to the electromagnetic stresses). We discuss the relevance of this system for possible multimessenger astronomy with binary black holes.

Yi Pan, University of Maryland

Analytical modeling of binary black-hole coalescence within the effective-one-body formalism.

I will review recent advances in the effective-one-body formalism aimed at describing the dynamics and gravitational-wave emission from coalescing black holes. I will discuss the implications of those advances for the search of gravitational waves from binary black holes and for the recoil velocity of black holes formed through merger.

Denis Pollney, Universitat de les Illes Balears

Nonlinear memory in numerical waveforms.

In addition to the dominant oscillatory modes gravitational waves contain non-oscillatory components which arise as drifts or offsets in the signals. Nonlinear gravitational memory arises from a change in mass multipole moments of a boundsystem due to contributions from the emitted gravitationalwaves. In practice it appears as a slowly monotonically growingsignal during the inspiral which sees a rapid rise at thetime of merger. The low amplitude and non-oscillatory natureof these signals present unique challenges for modeling.I discuss recent efforts to evaluate these signals in numericalsimulations using characteristic extraction as well as theirpotential relevance to detection.

Vivien Raymond, Northwestern University

Parameter estimation and model selection using spinning hybrid waveforms.

Most searches with ground-based detectors for gravitational-wave signals from the inspirals of stellar-mass compact binaries use template based methods. Those work well for non-spinning systems but since the dimensionality of the parameter space of spinning waveforms is large a template bank search is not feasible. We describe Bayesian and Markov-chain Monte-Carlo methods for parameter estimation of spinning waveforms using hybrid spinning waveforms matching the ringdown from Numerical Relativity results. We compare those results when using post-Newtonian only waveforms. We explore the parameter space and discuss different ways to overcome its high dimensionality and multi-modality.

James Healy, Georgia Tech

Mergers of Binary Black Holes as Burst Sources

TBA

Ulrich Sperhake, Caltech/CSIC Barcelona

11 Orbit inspiral of unequal mass black-hole binaries

We present simulations of non-spinning unequal mass black-hole binaries with mass ratio q=1/4 covering approximately 11 orbits prior to coalescence and merger obtained with the moving puncture technique. Accuracy of the simulations and matching to post-Newtonian waveforms is discussed.

Riccardo Sturani, University of Urbino/INFN

Complete phenomenological spin-Taylor waveforms for generic spins

The quest for gravitational waves from binary inspiral is performed via matched filtering and thus requires a detailed knowledge of the signal. For non-precessing binaries complete analytic waveforms exist from inspiral to merger and ring-down. Here we present complete waveforms for generically spinning equal mass systems.They have been constructed by bridging the gap between the analytically known inspiral phase described by spin Taylor (T4) approximants in the restricted waveform approximation and the ring-down phase.  These two phases are connected by a phenomenological intermediate phase calibrated by confrontation with numerically generated waveforms.The values of the overlap integral between numerical waveforms and our semi-analitic ones range between 0.96 and 0.99.

Nicolas Yunes, Princeton University

Post-Netwonian Modeling of EMRIs and IMRIs

Gravitational wave data analysis of compact binary systems requires the use of matched filtering. This technique cross-correlates the data stream with a certain template that characterizes the gravitational wave signal. Successful parameterestimation thus requires an accurate model of the gravitational wave template. In this talk I will describe a new fast and accurate technique to model the gravitational wave signal from extreme-mass ratio inspirals. Such events consisting of a neutron star or solar mass black hole spiraling into a supermassive black hole  are staple sources of the Laser Interferometer Space Antenna. This new model combines the effective-one-body formalism of post-Newtonian theory and black hole perturbation theory leading to accurate waveforms both when the supermassive black hole spins and when it does not.

Michele Zanolin, ERAU and LIGO-MIT

Achievable Directional Reconstruction for Gravitational waves generated by Binary Systems.

Recently generated asymptotic expansions zanolin et al. arXiv:0912.0065 [gr-qc] showa frequentist approach to go beyond Fisher information assessments of the accuracy for maximum likelihood parameter estimations. In this talk we describe the application of these techniques to directional reconstruction fornumerical relativity waveforms.

Yosef Zlochower, Rochester Institute of Technology

Extreme Black-Hole Binaries

In this talk I will show recent results obtained by the RIT group fromsimulations of highly-spinning binaries including new data that givesnear maximal spins and high-mass ratio binaries. Simulations in bothof these regimes are numerically challenging. However asastrophysical binaries are expected to be highly-spinning and havehigh mass ratios accurate simulations in these regimes are crucialfor understanding the dynamics of realistic binaries.

Yuk Tung Liu, University of Illinois at Urbana Champaign

Funding provided in part by:

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