Participants and abstracts

ALLEN BruceOral
The LIGO discoveries: how to read the basic physics off the data
I will discuss the advanced LIGO observations of gravitational waves emitted by the final few orbits and merger of two black holes, including the main results as well as some of the "behind the scenes" details. I will also address the basic physics, much of which can be read directly off the raw detector data. Finally, I'll talk about what we might learn about such systems in the next few years, as more detectors come into operation and they become more sensitive.

BAKER JohnPoster
Estimating measurability of LISA black hole merger parameters with Bayesian techniques
Mergers of massive binary black hole systems are a prominent target of the LISA mission. Our understanding of the inferences about these systems which we will be able to make from LISA data remains incomplete. Even with idealized assumptions about instrument noise there are many detailed features of black hole merger signals and the LISA response making significant contributions to the ability to measure important system parameters. LISA parameter estimation studies commonly leave out potentially important signal features, or make coarse approximations. Using recently developed techniques for fast and accurate LISA signal modeling for non-spinning black hole mergers, we study the impact of signal features including the post-inspiral signals, sub-leading angular modes, and investigate the difference between Bayesian and Fisher-matrix inference estimates.

BECKWITH AndrewPoster
How a Minimum Time Step Leads to a Causal structure used to form Initial Entropy Production and High Frequency Gravitons, with 7 Subsequent Open Questions
We start where we use an inflaton value due to use of a scale factor .Also we use delta g (tt) ~ square of the minimum scale factor times an inflaton as the variation of the time component of the metric tensor in Pre-Planckian Space-time up to the Planckian space-time initial values. In doing so, we come up with a polynomial expression for a minimum time step, we can call delta t which leads to a development of the arrow of time. We show an inter relationship between the formation of the Arrow of time, and Causal structure, assuming the setting of H = 0 in the Friedman equation This in turn leads to entropy production at the start of causal structure in the onset of inflation. This then leads to three and a quarter pages of 7 open questions we think have to be answered, subsequently. NOTE that high frequency gravitational waves as specified are due to the 1/delta t entry in Equation (45) of the document which comes out to about 44 Hertz, which certainly is high frequency gravitational waves for the initial cosmological conditions

BELCZYNSKI KrzysztofOral
The ongoing LIGO search for gravitational-waves: BH-BH modeling
Advanced LIGO has so far announced detection of two firm and one candidate of black hole -- black hole (BH-BH) mergers. More detections are expected at any moment during the ongoing second advanced LIGO observational run. Are we going to see any neutron star -- neutron star (NS-NS) mergers or black hole -- neutron star (BH-NS) mergers? What will we learn from such detections? Or should we rather expect more of the same: BH-BH mergers? Astrophysical origin of the three LIGO BH-BH mergers is not yet known, but some preliminary tests are being put forward. I will present updated evolutionary predictions for NS-NS, BH-NS and BH-BH mergers to guide a discussion on the nature and origin of LIGO sources.

Dynamics of compact binary systems in scalar-tensor theories at the third post-Newtonian order
In the upcoming years, the observation of gravitational waves from inspiraling compact binary systems will allow us to test General Relativity in its strong field regime. Both the detection and precise determination of the physical parameters of gravitational waves require a bank of very accurate template gravitational waveforms. In order to constrain the deviations from General Relativity, one also has to build template waveforms in alternative theories of gravity. In this talk, I will focus on massless scalar-tensor theories and address the question of the dynamics of non-spinning compact binary systems at 3PN order in harmonic coordinates. This is needed in order to compute the scalar and gravitational waveforms at 2PN order. In particular, I will present our method which is based on a Fokker action adapted to the specificities of both the post-Newtonian formalism and ST theories. I will then derive the conserved energy and momentum at 3PN order.

Post-Newtonian modelling of inspiralling compact binaries
The gravitational wave detectors LIGO/VIRGO have discovered the signals generated by the coalescence of binary black holes at astronomical distances. The theoretical and numerical works on the two-body problem in general relativity play a very important role when deciphering and interpreting the gravitational wave signals. In this talk we present the state-of-the-art on post-Newtonian (PN) methods in GR, applied to the gravitational waveform generated during the inspiralling phase of coalescing black hole binaries. In particular we discuss recent developments on the fourth post-Newtonian (4PN) approximation.

BOCHNER BrettPoster
A Statistical Search for Small-Strain Burst Sources Proliferating in LIGO Time Series Data
With the profound discovery of a handful of strong-signal Binary Black Hole (BBH) coalescences, these objects are now verified as a primary LIGO gravitational wave (GW) source. These few spectacular events must therefore be the tip of a very large iceberg of a multitude of BBH coalescences which are too weak to be individually identified and detected. As we move from the "big discovery" phase of GW Astronomy to the business of detection productivity, it is crucial to scour the time series data for all recoverable signs of real GW events. In this student-led research project, an algorithm is designed and executed to search for excess coincidence between interferometers due to short-period bursts hiding in the LIGO Online Science Center (LOSC) database. Our algorithm and results so far are presented, with estimates of how recoverable such signals may be in the Advanced LIGO data.

Astrophysical Signatures of Black Hole Mergers
Numerical relativity simulations of binary black holes played a crucial role in the calculations of the expected gravitational wave signals that were just observed. In this talk, I will briefly review the history of simulation efforts to model binary black holes in their astrophysical environments. I will also present some exciting new results in the context of magnetohydrodynamical simulation, indicating that supermassive binary black hole sources might be also detectable in the electromagnetic spectrum in the not too distant future.

CHAUVINEAU BertrandPoster
On gravitational radiation in Brans-Dicke gravity
Brans-Dicke gravity admits spherical solutions describing naked singularities rather than black holes. On the ground of orbital motions in the corresponding metric, we discuss some expected properties of the expected gravitational radiation by EMRI systems involving such a naked singularity. We argue that, unlike what happens in General Relativity, such system can result in gravitational radiation with unbounded frequencies.

LISA Technology Development at the University of Florida
The LISA space gravitational wave observatory will measure picometer changes in the distances between free falling test masses separated by 2.5 million kilometers caused by gravitational waves. LISA will observe gravitational wave sources ranging from super-massive black hole mergers to compact galactic binaries in the millihertz region. LISA Pathfinder, launched in December of 2015, has successfully demonstrated key technologies for LISA, including the gravitational reference sensor and its closed loop drag-free operation. Yet there are a few key LISA technologies that still must be developed within the next few years. To this end, the University of Florida LISA group has constructed the UF Torsion Pendulum facility where new technologies can be developed and evaluated. This experimental facility is based on the design of a similar facility at the University of Trento, and consists of a vacuum enclosed torsion pendulum that suspends mock-ups of the LISA test masses, surrounded by electrode housings. We are using this facility to test the performance of a novel test mass charge control system utilizing UV LEDs under development at UF for LISA. The UF LISA group is also researching alternate schemes for passing laser phase information between LISA’s two moving optical benches. This ‘free-space backlink’ will be evaluated using a unique precision mechanical apparatus that simulates the motion of LISA’s optical benches in the laboratory. This presentation will describe these activities and provide the latest experimental results.

LISA is not LIGO in space
The good news is that the LISA mission is back! The bad news is that we have less than a decade to figure out how to analyze the data. Experience gained from analyzing LIGO/Virgo data and PTA data will certainly be valuable, but the LISA data will presents unique challenges that demand new solutions. The LISA data will contain millions of sources that overlap in time and frequency. The noise will be non-stationary on the timescale of the signals. Many of the signals will be extremely complex, with eccentricity, spin precession and large mass ratios playing important roles. The core issue is that the solution does not separate - we must simultaneously solve for tens of thousands of resolvable signals and the time-varying noise to arrive at a global solution. I will sketch out a plan for how this can be done.

CUSIN GiuliaOral
Anisotropy of the astrophysical gravitational wave background: angular power spectrum and correlation with cosmological observations
Unresolved sources of gravitational waves are at the origin of a stochastic gravitational wave background. While the computation of its mean density as a function of frequency in a homogeneous and isotropic universe is standard lore, the computation of its anisotropies requires to understand the coarse graining from local systems, to galactic scales and then to cosmology. An expression of the gravitational wave energy density valid in any general spacetime is derived. It is then specialized to a perturbed Friedmann-Lemaˆitre spacetime in order to determine the angular power spectrum of this stochastic background as well as its correlation with other cosmological probes, such as the galaxy number counts and weak lensing. Our result for the angular power spectrum also provides an expression for the variance of the GW background.

DAMOUR ThibaultOral
The Effective-One-Body Approach to Compact Binaries and its Synergy with Other Approaches
The construction, within the Effective-One-Body (EOB) formalism, of a large bank of (semi-)analytical binary black-hole merger templates has been crucial in the search, significance assessment and parameter estimation of the merger signals detected by LIGO. Besides providing new results of its own (starting with the first estimate of the complete binary-black-hole merger waveform), the EOB formalism is a framework within which the results of several other approximation methods (post-Newtonian, post-Minkowskian, Numerical Relativity, Black Hole perturbation, Self-Force) can be usefully combined, thereby extending the realm of validity of the original methods. A review of the EOB formalism and of its synergies with other approaches will be presented.

DE MINK SelmaOral
Progenitors of LIGO's black holes
What physical processes govern the lives of the progenitors of LIGO's black holes? What can we learn about the stars that likely gave birth to them? I will discuss the key challenges that every progenitor models faces and briefly review the main ideas that are under consideration, focussing on the evolutionary channels.

DENT ThomasPoster
Detecting compact binary mergers with Advanced LIGO: Improving the sensitivity of the PyCBC search
We present an improved search for binary compact-object mergers using a network of ground-based gravitational-wave detectors. We model a volumetric, isotropic source population and incorporate the resulting distribution over signal amplitude, time delay, and coalescence phase into the ranking of candidate events. We describe an improved modeling of the background distribution, and demonstrate incorporating a prior model of the binary mass distribution in the ranking of candidate events. We find a ~ 10% and ~ 20% increase in detection volume for simulated binary neutron star and binary black hole systems, respectively, corresponding to a reduction of the false alarm rate assigned to signals by between one and two orders of magnitude.

Measuring the stochastic gravitational-wave background from stalling massive black-hole binaries
Massive black hole binaries, formed when galaxies merge, are among the primary sources of gravitational waves targeted by ongoing Pulsar Timing Array (PTA) experiments and the upcoming space-based LISA interferometer. However, their formation and merger rates are highly uncertain and recent upper limits on the stochastic gravitational-wave background obtained by PTAs are starting to be in marginal tension with theoretical models. While several mechanisms were proposed to resolve this tension, one particularly worrisome possibility is that black hole binaries do not merge efficiently, but stall at large separations. In this talk I will show that future generations of PTAs will detect the stochastic gravitational-wave background from the massive black-hole binary population even if all the black hole binaries stall. Moreover, I will argue that a sub-population of binaries with small mass ratios, predicted by our model, should merge within a Hubble time simply as a result of gravitational-wave emission. This sub-population will be observable with large signal-to-noise ratios by future PTAs and possibly by LISA.

GAYATHRI VivekananthaswamyOral
Wavelet-based search of coalescing compact binaries with GW detectors
The first direct detection of gravitational waves from binary black holes has opened the new era of gravitational wave astronomy. Besides binary black holes, compact binaries with two neutron stars as well as neutron star/black hole systems emit transient gravitational waves that can be detected by interferometric detectors. Coherent WaveBurst is a unmodeled and wavelet-based detection pipeline for all-sky and all-time searches for short-duration gravitational wave transients. Here, we present Wavegraph, an alternative time-frequency clustering scheme integrated to coherent WaveBurst which is dedicated to chirp-like signals such as compact binary coalescence signals. We give a description of this algorithm and its performance with real detector data.

HAN WenbiaoOral
Fully numerical calibrated waveforms for extreme-mass-ratio-insprials in effective-one-body frame
Extreme-mass-ratio-inspirals (EMRIs) are composed by supermassive black holes and stellar mass compact bodies, and they are very important gravitational wave sources for the space-based detectors like as eLISA, Taiji and Tianqin. How to calculate the gravitational waves (GWs) of EMRIs in a highly accurate and efficient way still keep a challenge. In this presentation, I introduce our recent work on the modeling of waveforms from EMRIs in the effective-one-body (EOB) formalism. Firstly, I will give a simple overview of the numerical simulation for EMRIs, i.e., the Teukolsky equations. Secondly, EOB dynamics and resummed-calibation waveforms are introduced and we show the accuracy of the original EOB waveforms. Finally, I will discuss in details about our new fully calibrated method for EOB waveforms based on the highly precise numerical data. We demonstrate the accuracy and efficient of our new fully calibrated models, which are much higher than the existed models. I believe our model will play an important role in the waveform template construction of eLISA, Taiji and Tianqin.

Scalar Tensor Waveforms to second post-Newtonian order
Testing alternative theories of gravity in the strong-field gravitational-wave regime can be an important complement to solar-system tests. A leading alternative is the class of scalar-tensor theories; for binary systems of compact objects, equations of motion and the tensor waveform and energy flux have been derived through second post-Newtonian (2PN) order. However, because the scalar field in these theories admits dipole gravitational radiation, a calculation of the scalar contribution to the energy flux requires calculating the scalar field and the equations of motion to 3PN order. We report on progress toward completing this calculation and obtaining waveforms to 2PN order, suitable for gravitational-wave data analysis.

An eccentric binary black hole inspiral-merger-ringdown gravitational waveform model from numerical relativity and post-Newtonian theory
I present a prescription for computing gravitational waveforms for the inspiral, merger and ringdown of non-spinning eccentric binary black hole systems. Eccentric numerical relativity (NR) waveforms are used to calibrate and test the resulting eccentric waveform model. The inspiral waveform is computed using the post-Newtonian expansion and the merger waveform is computed by interpolating a small number of quasi-circular NR waveforms. The use of circular merger waveforms is possible because eccentric binaries circularise in the last few cycles before the merger, which we demonstrate using NR. I describe how the model is constructed, and discuss how well it agrees with the NR simulations, including faithfulness calculations relevant to gravitational wave detectors.

HWANG Jai-chanOral
Gauge dependence of gravitational waves generated from scalar perturbations
A tensor-type cosmological perturbation, defined as a transverse and traceless spatial fluctuation, is often interpreted as the gravitational waves. While decoupled from the scalar-type perturbations in linear order, the tensor perturbations can be sourced from the scalar-type in the nonlinear order. The tensor perturbations generated by the quadratic combination of linear scalar-type cosmological perturbation are widely studied in the literature, but all previous studies are based on zero-shear gauge without proper justification. Here, we show that, being second order in perturbation, such an induced tensor perturbation is generically gauge dependent. In particular, the gravitational wave power spectrum depends on the hypersurface (temporal gauge) condition taken for the linear scalar perturbation. We also show that the induced tensor modes must be modeled correctly specific to the observational strategy for the measurement of primordial gravitational waves from large-scale structure via, for example, parity-odd mode of weak gravitational lensing, or clustering fossils.

Formation of stellar-mass binary black holes and identifying their origins
Advanced LIGO has detected sources of gravitational waves (GWs). The sources, GW150914, GW151226 and LVT151012, are inferred to be merging binary black holes (BBHs). The origin of such massive and compact BBHs and their formation pathways have been proposed through massive binary evolution and/or stellar dynamics in a dense stellar system. In my talk, I first focus on a BBH formation channel via binary evolution of Population III stars. This scenario potentially produce a strong GW background, which is detectable by LIGO/Virgo O5 observing run. Next, I will talk about a new idea about how to distinguish the formation channels of LIGO-BBHs with multi-frequency GW observations by LIGO and LISA.

JULIÉ Félix-LouisOral
Two-body problem in Scalar-Tensor theories : an Effective-One-Body approach
We address the two-body problem in massless Scalar-Tensor (ST) theories within an Effective-One-Body (EOB) framework. We focus on the first building block of the EOB approach, that is, mapping the conservative part of the two-body dynamics onto the geodesic motion of a test particle in an effective external metric. A ST-deformation of the general relativistic EOB Hamiltonian is built, and allows to incorporate the Scalar-Tensor (2PK) corrections to the currently best available General Relativity EOB results. This EOB-ST Hamiltonian defines a resummation of the dynamics that may provide information on the strong-field regime, in particular, the ISCO location and associated orbital frequency.

Analytical gravitational self-force
I will discuss the utility of post-Newtonian expansions in the gravitational self-force approach to describing extreme mass-ratio inspirals and their application via gauge invariant relations to determining coefficients in the potentials of the effective-one-body model.

KIDDER LawrenceOral
Gravitational waveforms from numerical simulations of binary-black-hole mergers
Numerical solutions of the vacuum Einstein field equations are used to model the late inspiral and merger of two black holes, and to compute the emitted gravitational waveforms. In the era of gravitational wave astronomy, these waveforms are invaluable tools for data analysts and waveform modelers. The numerical waveforms can be: directly compared to observations; used to inform and test analytic waveform models such as the effective one-body and phenomenological approaches; and used to construct surrogate models. In addition to the waveforms, the numerical solutions provide the properties of the remnant black hole, and can be used to explore highly dynamical spacetimes.

Gravitational wave bursts: Detection with minimal assumptions
Discovery of gravitational waves by LIGO opens a new window on Universe. Soon LIGO will be complemented by other gravitational wave instruments to form a world-wide network of detectors. Combined with other astronomical instruments it will enable multi-messenger observations of astrophysical events dramatically expanding our means to study cosmos. Anticipated and possibly entirely new gravitational-wave sources are likely to be discovered – we should be ready for unexpected. In the talk I describe the detection of transient (burst) sources with poorly known or uncertain models. Robust methods for source localization, reconstructions of the signal waveforms and polarization are presented. Astrophysical implications of the source reconstruction and how it is affected by the network configuration are discussed.

LE TIEC AlexandreOral
Horizon surface gravity in black hole binaries
For binary systems of co-rotating black holes, the zeroth law of mechanics states that the surface gravity is constant over each component of the horizon. In this talk, we will discuss the recent calculation of this physical quantity in sequences of quasi-equilibrium initial data for binary black holes with mass ratios in the range 10:1-1:1. We compared those numerical results to the analytical predictions from post-Newtonian theory at the fourth (4PN) order and from black hole perturbation theory to linear order in the mass ratio. We found a remarkably good agreement for all mass ratios considered, even in the strong-field regime. In particular, this confirms that black hole perturbation theory may turn out to be useful in the modeling of intermediate mass-ratio inspirals or even binaries with comparable masses.

LEE Hyung MokOral
Dynamical Formation of Black Hole Binaries in Dense Stellar Systems
The advanced detectors of gravitational waves detected three black hole binary mergers and one candidate. Such binaries are either formed by evolution of massive binary systems or through dynamical processes in dense stellar systems. I will focus on the dynamical scenarios originating from globular clusters. The galactic nuclei star clusters (NC) could also provide suitable environment for the dynamical binary formation, but they are likely to be much less efficient than globular clusters. In globular clusters, the black holes become the most massive components within 10 million years after the birth of the clusters. The black holes experience dynamical friction that causes central concentration of massive black hoes in the central parts of the clusters in a short time scale. Black hole binaries can be formed either direct capture or by three-body processes in dense core. Under typical conditions of globular clusters, three-body processes are much more efficient than direct capture. The binaries experience subsequent interactions with surrounding stars (mostly black holes) and the orbit shrinks due to such interactions. Eventually the bianries get ejected along with surrounding black holes, leading to nearly complete desertification of black holes in the cluster in a few billion years. The ejected binaries undergo passive evolution outside the cluster through gravitational radiation. Some fraction of the them will merge within Hubble time. We expect the mass ratios of two black holes in binaries would be close to unity. Binaries composed of a black hole and a neutron star will be very rare among dynamical binaries. The rate of merger is rather uncertain, but likely to be about 10 per year per cubic giga parsec, roughly consistent with the current estimation based on the detected events.

Facing the challenge of testing GR with gravitational waves
Exploiting gravitational waves to probe the underlying gravitational theory requires a thorough understanding of possible surprises in GR, as well as possible departures from it. In this talk i will discuss a few interrelated challenges in this task and ways to address them.

4.5 Post-Newtonian order gravitational radiation
Post-Newtonian theory enables us to predict the waveform of the gravitational waves emitted by a system of two compact objects coalescing in its inspiral phase. State-of-the-art works provide the phase of the expected signal up to 3.5PN (i.e. up to 1/c^7). Comparison with numerical relativity, as well as the promising evolution of gravitational wave detectors incite us to pursue this computation to a higher order. In our current attempt, we are reaching the phase of the signal at the 4.5PN order (i.e. 1/c^9). For this purpose, the flux emitted by such a system has to be known at 4.5PN. One difficulty of this computation is the high-order interactions - commonly called tails- between the mass of the system and its mass and current multipole moments during the propagation of the signal. In [1], we have computed the contribution of all the tails entering the flux at 4.5PN, and in particular the third-order mass-quadrupole interactions known as "tails-of-tails-of-tails". Our work enables to fully determine the 4.5PN coefficient of the flux (while the 4PN coefficient is still unknown). [1] Marchand T., Blanchet L., Faye G. Class.Quant.Grav. 33 (2016) no.24, 244003

MARSAT SylvainOral
Fourier-domain response and Bayesian parameter estimation for LISA
The future space-based gravitational-wave detector LISA will detect mergers of black hole binaries up to high redshift, and produce a wealth of observations complementing the ground-based detectors LIGO/Virgo. In the past, due to computational cost limitations, most prospective studies of source parameter recovery relied on a simplified response of the instrument, on inspiral-only waveform models and on the Fisher matrix approximation. We present a Fourier-domain approach to handle the full time-dependent modulations of the signal induced by the orbital motion of the detector. By combining our approach with recently developed fast and accurate Fourier-domain waveform models that include the merger and ringdown, we are able to bring down the cost of likelihood evaluations to a few milliseconds, thus opening the way to extensive Bayesian analyses. We also discuss the application of our formalism to the precession-induced modulations in the signals of spinning binaries.

MIKOCZI BalazsOral
Does the gravitational waveform depend on the spin supplementary conditions?
I will discuss the different spin supplementary conditions (SSC) for a spinning compact binary with the leading-order spin-orbit (SO) interaction. The Lagrangian of the binary system can be constructed, but it is acceleration-dependent in two cases of SSC. I will also show the generalized Hamiltonian formalism proposed by Ostrogradsky and compute the conserved quantities, i.e. the orbital elements of the SO dynamics and the dissipative part of relative motion during the gravitational radiation of each SSC. I will give the energy and the orbital angular momentum losses and waveforms, and discuss their SSC dependence.

Gravitational waves from core collapse supernovae
In the talk I will review the past efforts to predict the gravitational wave signature of core collapse supernova explosions, and present theoretical wave forms and spectra obtained from recent 3D core collapse supernova simulations which, if observed, can provide important, direct information about the explosion mechanism.

NEROZZI AndreaOral
Towards an advanced wave extraction algorithm in numerical relativity
With the recent detection of gravitational waves and the expected improvements in accuracy of current and future experiments, it is of primary importance that numerical simulations achieve higher degrees of accuracy as well. In particular, the process extracting gravitational waveforms from numerical simulations can be still subject by possible systematic errors, mostly because of the gauge freedom that is encountered along the way. I will present recent results in the field of wave extraction using the Newman-Penrose (NP) formalism, specifically aiming to remove all gauge ambiguities in the calculation of the NP quantities at finite radius. I will also discuss possible extensions of this methodology to obtain a gauge fixed signal at null infinity.

NOH HyerimOral
Gauge dependence of gravitational waves generated from scalar perturbations
I am the co-author of "Gauge dependence of gravitational waves generated from scalar perturbations", and the first author, Dr. Jai-chan Hwang will have a presentation.

OLTEAN MariusOral
The particle-without-particle approach to the self-force problem
The gravitational waves emitted by binary systems with extreme or intermediate mass ratios carry unique astrophysical information expected to be probed by the next generation of gravitational wave detectors. The detection of these binaries rely on an accurate modelling of the gravitational self-force that drives their orbital evolution. Although the theoretical formalism to compute the self-force has been largely established, the mathematical tools needed to implement it are still under development, and the self-force computation remains an open problem. The main difficulties arise from the singular nature of the terms appearing in the equations of motion due to the "point source" modeling of the inspiraling compact object. We present a practical pseudospectral collocation method designed to circumvent these difficulties, called the "particle-without-particle" technique. In particular, we illustrate the broad and adaptable features of our numerical implementation within some simple differential equation models, and we discuss its application to the frequency-domain calculation of the the scalar self-force -- a helpful testbed for the gravitational self-force.

OLTEAN MariusPoster
Entropy theorems in classical mechanics, general relativity, and the gravitational two-body problem
In classical Hamiltonian theories, entropy may be understood either as a statistical property of canonical systems, or as a mechanical property, that is, as a monotonic function of the phase space along trajectories. In classical mechanics, there are theorems which have been proposed for proving the non-existence of entropy in the latter sense. We explicate, clarify and extend the proofs of these theorems to some standard matter (scalar and electromagnetic) field theories in curved spacetime, and then we show why these proofs fail in general relativity; due to properties of the gravitational Hamiltonian and phase space measures, the second law of thermodynamics holds. As a concrete application, we focus on the consequences of these results for the gravitational two-body problem, and in particular, we prove the non-compactness of the phase space of perturbed Schwarzschild-Droste spacetimes. We thus identify the lack of recurring orbits in phase space as a distinct sign of dissipation and hence entropy production.

OULD EL HADJ MohamedOral
Waveforms produced by a particle plunging into a black hole in massive gravity: Excitation of quasibound states and quasinormal modes
We determine the waveform generated by a particle plunging from slightly below the innermost stable circular orbit into a Schwarzschild black hole and analyze its spectral content. We work, at first, with a “toy-model” where the graviton field is replaced by a massive scalar field linearly coupled to the plunging particle, such a toy model permitting us to exhibit and interpret some important effects. Then, we show that these effects are also present in massive gravity and could be used to test these extensions of general relativity.

PIRAN TsviOral
GRBs, Macronova, Cocoon Emission and Radio Flares
I describe different electromagnetic counterparts to neutron star mergers. These include short Gamma-Ray Bursts, Macronova (also called kilonova), Cocoon Emission (a recently discovered short bright component) and a Radio flare that arises on a time scale of years.

RAMOS OscarOral
Testing Lorentz Invariance by Binary Black Holes
The recent detection of gravitational waves has opened a new avenue towards the highly-relativistic and dynamical strong-field regime of the Einstein equations. It's therefore possible to test GR in a new arena characterized by velocities comparable to the speed of light and by large, dynamical curvatures. We will focus upon one particular alternative to GR: Lorentz-violating gravity. Although Lorentz-invariance is at the heart of theoretical physics, its violation in the gravitational sector may lead to a quantum theory of gravitation, for instance. Thus, we will show how GW signals can be used to test Lorentz-violating theories.

REITZE DavidOral
Ground-based Gravitational-wave Detectors: Prospects for the Future
The detection of gravitational waves produced during the collision of two black holes, while remarkable, has only given us the first glimpses into this new realm of the universe. In order to fully explore the gravitational-wave landscape, new detectors are needed which will greatly expand our reach into the cosmos. In this talk, I'll (briefly) give a status report on the current LIGO-Virgo 'O2' observing run and then turn to plans for the future for improving the existing LIGO detectors' sensitivity as well as plans under development for a new generation of ground-based detectors.

SESANA AlbertoOral
The future of gravitational wave detection: the low frequency band
Following detection by advance LIGO, gravitational wave (GW) stocks are on the rise. The low frequency GW Universe is likely dominated by signals emitted by a cosmological population of massive black hole binaries (MBHBs). I will review several aspect of MBH astrophysics, including their formation, evolution, interaction with their environment and GW emission. I will then discuss prospect of GW detection with pulsar timing arrays and/or future space based interferometers such as the laser interferometer space antenna (LISA).

SHARMA PranavPoster
Multiple Black Holes in Active Galactic Nuclei: Inspiral, Hardening and Merger
In the wake of the gravitational wave era when the universe has suddenly started speaking a recently known language of space-time crests and troughs, it has become important to investigate systems which would potentially emanate gravitational waves. In our study, we investigate the inspiral, hardening and merger mechanisms of multiple black holes in the active galactic nuclei. We also investigate the slingshot mechanisms over various stalling black holes in the disk and their observational consequences, primarily gravitational waves.

SHIBATA MasaruOral
Gravitational waves from neutron-star binaries
I will talk on our current understanding of gravitational waves emitted from neutron star binaries (binary neutron stars and black hole-neutron star binaries) based on the latest results of numerical-relativity simulations. I will focus in particular on the effects of neutron-star equations of state on gravitational waveforms.

SIEMENS XavierOral
The Discover Potential of Pulsar Timing Arrays
For over a decade, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank and Arecibo radio telescopes to monitor millisecond pulsars. NANOGrav, along with similar international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small correlated changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will give a status update and discuss the work of NANOGrav, as well as our sensitivity to gravitational waves from astrophysical sources.

SOARES Ivano DamiaoPoster
Gravitational Wave Luminosity and Net Momentum Flux in Head-on Mergers of Black Holes: Radiative Patterns and Mode-Mixing
We show that gravitational wave radiative patterns from a point test particle falling radially into a Schwarzschild black hole, as derived by Davis, Ruffini, Press and Price (Phys. Rev. Lett. 27, 1466 (1971)), are present in the nonlinear regime of head-on mergers of black holes. We use the Bondi-Sachs characteristic formulation and express the gravitational wave luminosity and the net momentum flux in terms of the news functions. We then evaluate the (-2)-spin-weighted l-multipole decomposition of these quantities via exact expressions valid in the nonlinear regime and defined at the future null infinity. We obtain an accurate exponential decay with l of the total energy contributed by each multipole l, up to a mass ratio alpha ~0.7 . Above this mass ratio the contribution of the odd modes to the energy decreases faster than that of the even modes, leading to the breaking of the linear correlation. The dominant contribution to the total radiated energy comes from the quadrupole mode l=2 corresponding, for instance, to about ~84\% for small mass ratios up to ~99.8\% for the limit case alpha=1. The total rescaled radiated energy Etotal/m_0 alpha^2 decreases linearly with decreasing alpha, yielding for the point particle limit alpha~0 the value ~0.0484, about five times larger than the result of Davis et al. The mode decomposition of the net momentum flux and the associated gravitational wave impulses results in an adjacent-even-odd mode-mixing pattern. The impulses contributed by each (l,l+1) mixed mode satisfy accurately an exponential decay with l, for the whole mass ratio domain considered, alpha =[0.01, 1]. The (2,3) mode contribution to the total impulses are dominant. The mixed mode impulses reach a maximum at alpha~0.7 and decrease to zero at the equal mass case alpha=1.

LIGO-India: Beyond discovery of Gravitational waves.
The historic discovery of gravitational waves through direct detection by the LIGO observatories in the USA, in principle, opens up a new window for astronomy.  In practice, however, the true launch of gravitational-wave astronomy  will await  the global array of LIGO-like observatories including the planned LIGO-India  observatory recently flagged off by the Union cabinet of India. I will review the momentous discovery, the potential of gravitational-wave astronomy, the status and promise of LIGO-India.

Measuring the peculiar acceleration of binary black holes with LISA
Multi-frequency gravitational wave (GW) observations are useful probes of the formation processes of coalescing stellar-mass binary black holes (BBHs). In this talk I will show how the cosmic acceleration of the universe and the peculiar acceleration of the center-of-mass of a merging BBH, distort the gravitational chirp signal by a phase drift in the GW inspiral waveform. The effect due to the peculiar acceleration can be much larger than the one due to the universe acceleration, strongly depending on the location where a BBH forms within a galaxy. For BBHs formed in dense nuclear star clusters or via compact accretion disks around a nuclear supermassive black hole, the phase drift can be large enough to be measured by LISA, allowing for an independent probe of the nuclear formation channels to the stellar-mass BBH population. I will present forecasts on the accuracy with which LISA will be able to measure this peculiar acceleration effect, with and without coincident observations by Earth-based interferometers.

LISA 2017: A New Beginning
The twin achievements of the first direct detection of gravitational waves by LIGO and the successful demonstration of precision drag-free flight by LISA Pathfinder have altered the landscape for space-based gravitational wave observatories. The appetite for gravitational wave science is great and we have the technology to produce the feast that a space-based observatory will provide. In this talk, I will describe the current vision for the Laser Interferometer Space Antenna (LISA) with an overview of its science case, technologies, mission design, and implementation strategies.

VAN DE MEENT MaartenOral
Modelling EMRIs using Self-Force
Extreme mass ratio inspirals are a key science target for LISA. I will review the progress in modelling gravitational wave signal from these systems using systematic expansion in the mass ratio of the binary.

Testing general relativity with gravitational waves
The discovery of the gravitational wave signals GW150914, GW151226 and GW170104 with Advanced LIGO has, for the first time, given us direct empirical access to the genuinely strong-field dynamics of spacetime. I describe the tests of general relativity that were performed with these events, regarding the inspiral-merger-ringdown dynamics of binary black hole coalescences as well as the propagation of gravitational waves over large distances. I also discuss tests that can be performed with louder events and upgrades of the current detectors.

VINET Jean-YvesOral
Gravitational Wave Detection
We recall the physics behind the existing or planned instruments for detecting gravitational waves in the different frequency ranges

Massive black hole binaries in the cosmos
I will discuss and review the dynamics of massive black hole binary formation and mergers, as well as critically assess and compare predictions for the merger rate of massive black holes detectable with LISA and PTA.

WHITING BernardOral
A stochastic gravitational-wave background from binary black hole mergers
The whole world was excited to hear that the first, directly detected, gravitational waves arose from the merger of two black holes of about 30 solar masses at a redshift close to 0.1. The existence of black holes of such mass, and of binaries composed of such black holes, raises new questions about the abundance of such sources and of their possible origins. In this talk we will discuss implications of the existence of such sources and the potential that, at higher redshifts, they may create an unresolved stochastic background of gravitational waves.

WILLIS JoshuaOral
A new method for incorporating precession and higher-order modes in searches for compact binaries
Advanced LIGO's current matched-filter searches for binary mergers model only the dominant mode of binaries whose orbital angular momentum is aligned with the total angular momentum. Some models of binary formation predict a population of systems where these simplifying assumptions will not hold, and so a search that includes them may be necessary to discriminate between these models. In this talk we describe a new technique for including the effects of higher-order modes and precession, that directly maximizes the likelihood over extrinsic parameters without a grid search.

UMR7095 - Institut d'Astrophysique de Paris - 98 bis boulevard Arago - 75014 Paris