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Chris Van Den Broeck

Publications and source records attributed to Chris Van Den Broeck.

At least 73 records · Page 4Linked to original sources
arXiv2019

Modeling the postmerger gravitational wave signal and extracting binary properties from future binary neutron star detections

Gravitational wave astronomy has established its role in measuring the equation of state governing cold supranuclear matter. To date and in the near future, gravitational wave measurements from neutron star binaries are likely to be restricted to the inspiral. However, future upgrades and the next generation of gravitational wave detectors will enable us to detect the gravitational wave signatures emitted after the merger of two stars, at times when densities beyond those in single neutron stars are reached. Therefore, the postmerger gravitational wave signal enables studies of supranuclear matter at its extreme limit. To support this line of research, we present new and updated phenomenological relations between the binary properties and characteristic features of the postmerger evolution. Most notably, we derive an updated relation connecting the mass-weighted tidal deformability and the maximum neutron star mass to the dominant emission frequency of the postmerger spectrum. With the help of a configuration-independent Bayesian analysis using simplified Lorentzian model functions, we find that the main emission frequency of the postmerger remnant, for signal-to-noise ratios of $8$ and above, can be extracted within a 1-sigma uncertainty of about 100 Hz for Advanced LIGO and Advanced Virgo's design sensitivities. In some cases, even a postmerger signal-to-noise ratio of $4$ can be sufficient to determine the main emission frequency. This will enable us to measure binary and equation-of-state properties from the postmerger, to perform a consistency check between different parts of the binary neutron star coalescence, and to put our physical interpretation of neutron star mergers to the test.

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arXiv2019

A morphology-independent search for gravitational wave echoes in data from the first and second observing runs of Advanced LIGO and Advanced Virgo

Gravitational wave echoes have been proposed as a smoking-gun signature of exotic compact objects with near-horizon structure. Recently there have been observational claims that echoes are indeed present in stretches of data from Advanced LIGO and Advanced Virgo immediately following gravitational wave signals from presumed binary black hole mergers, as well as a binary neutron star merger. In this paper we deploy a morphology-independent search algorithm for echoes introduced in Tsang et al., Phys. Rev. D 98, 024023 (2018), which (a) is able to accurately reconstruct a possible echoes signal with minimal assumptions about their morphology, and (b) computes Bayesian evidences for the hypotheses that the data contain a signal, an instrumental glitch, or just stationary, Gaussian noise. Here we apply this analysis method to all the significant events in the first Gravitational Wave Transient Catalog (GWTC-1), which comprises the signals from binary black hole and binary neutron star coalescences found during the first and second observing runs of Advanced LIGO and Advanced Virgo. In all cases, the ratios of evidences for signal versus noise and signal versus glitch do not rise above their respective "background distributions" obtained from detector noise, the smallest $p$-value being 3% (for event GW170823). Hence we find no statistically significant evidence for echoes in GWTC-1.

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arXiv2019

Testing the multipole structure and conservative dynamics of compact binaries using gravitational wave observations: The spinning case

In an earlier work [S. Kastha et al., PRD {\bf 98}, 124033 (2018)], we developed the {\it parametrized multipolar gravitational wave phasing formula} to test general relativity, for the non-spinning compact binaries in quasi-circular orbit. In this paper, we extend the method and include the important effect of spins in the inspiral dynamics. Furthermore, we consider parametric scaling of PN coefficients of the conserved energy for the compact binary, resulting in the parametrized phasing formula for non-precessing spinning compact binaries in quasi-circular orbit. We also compute the projected accuracies with which the second and third generation ground-based gravitational wave detector networks as well as the planned space-based detector LISA will be able to measure the multipole deformation parameters and the binding energy parameters. Based on different source configurations, we find that a network of third-generation detectors would have comparable ability to that of LISA in constraining the conservative and dissipative dynamics of the compact binary systems. This parametrized multipolar waveform would be extremely useful not only in deriving the first upper limits on any deviations of the multipole and the binding energy coefficients from general relativity using the gravitational wave detections, but also for science case studies of next generation gravitational wave detectors.

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arXiv2019

Testing the multipole structure of compact binaries using gravitational wave observations

We propose a novel method to test the consistency of the multipole moments of compact binary systems with the predictions of General Relativity (GR). The multipole moments of a compact binary system, known in terms of symmetric and trace-free tensors, are used to calculate the gravitational waveforms from compact binaries within the post-Newtonian (PN) formalism. For nonspinning compact binaries, we derive the gravitational wave phasing formula, in the frequency domain, parametrizing each PN order term in terms of the multipole moments which contribute to that order. Using GW observations, this {\it{parametrized multipolar phasing}} would allow us to derive the bounds on possible departures from the multipole structure of GR and hence constrain the parameter space of alternative theories of gravity. We compute the projected accuracies with which the second generation ground-based detectors, such as Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), the third generation detectors such as Einstein Telescope and Cosmic Explorer, as well as space-based detector Laser Interferometer Space Antenna (LISA) will be able to measure these multipole parameters. We find that while Advanced LIGO can measure the first two or three multipole coefficients with good accuracy, Cosmic Explorer and Einstein Telescope may be able to measure the first four multipole coefficients which enter the phasing formula. Intermediate mass ratio inspirals, with mass ratio of several tens, in the frequency band of planned space-based LISA mission should be able to measure all the seven multipole coefficients which appear in the 3.5PN phasing formula. Our finding highlights the importance of this class of sources for probing the strong-field gravity regime. The proposed test will facilitate the first probe of the multipolar structure of Einstein's general relativity.

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arXiv2018

Empirical tests of the black hole no-hair conjecture using gravitational-wave observations

We show that second-generation gravitational-wave detectors at their design sensitivity will allow us to directly probe the ringdown phase of binary black hole coalescences. This opens the possibility to test the so-called black hole no-hair conjecture in a statistically rigorous way. Using state-of-the-art numerical relativity-tuned waveform models and dedicated methods to effectively isolate the quasi-stationary perturbative regime where a ringdown description is valid, we demonstrate the capability of measuring the physical parameters of the remnant black hole, and subsequently determining parameterized deviations from the ringdown of Kerr black holes. By combining information from $\mathcal{O}(5)$ binary black hole mergers with realistic signal-to-noise ratios achievable with the current generation of detectors, the validity of the no-hair conjecture can be verified with an accuracy of $\sim 1.5\%$ at $90\%$ confidence.

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arXiv2018

A morphology-independent data analysis method for detecting and characterizing gravitational wave echoes

The ability to directly detect gravitational waves has enabled us to empirically probe the nature of ultra-compact relativistic objects. Several alternatives to the black holes of classical general relativity have been proposed which do not have a horizon, in which case a newly formed object (e.g. as a result of binary merger) may emit echoes: bursts of gravitational radiation with varying amplitude and duration, but arriving at regular time intervals. Unlike in previous template-based approaches, we present a morphology-independent search method to find echoes in the data from gravitational wave detectors, based on a decomposition of the signal in terms of generalized wavelets consisting of multiple sine-Gaussians. The ability of the method to discriminate between echoes and instrumental noise is assessed by inserting into the noise two different signals: a train of sine-Gaussians, and an echoing signal from an extreme mass-ratio inspiral of a particle into a Schwarzschild vacuum spacetime, with reflective boundary conditions close to the horizon. We find that both types of signals are detectable for plausible signal-to-noise ratios in existing detectors and their near-future upgrades. Finally, we show how the algorithm can provide a characterization of the echoes in terms of the time between successive bursts, and damping and widening from one echo to the next.

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arXiv2018

Matter imprints in waveform models for neutron star binaries: tidal and self-spin effects

The combined observation of gravitational and electromagnetic waves from the coalescence of two neutron stars marks the beginning of multi-messenger astronomy with gravitational waves (GWs). The development of accurate gravitational waveform models is a crucial prerequisite to extract information about the properties of the binary system that generated a detected GW signal. In binary neutron star systems (BNS), tidal effects also need to be incorporated in the modeling for an accurate waveform representation. Building on previous work [Phys.Rev.D96 121501], we explore the performance of inspiral-merger waveform models that are obtained by adding a numerical relativity (NR) based approximant for the tidal part of the phasing (NRTidal) to existing models for nonprecessing and precessing binary black hole systems (SEOBNRv4, PhenomD and PhenomPv2), as implemented in the LSC Algorithm Library Suite. The resulting BNS waveforms are compared and contrasted to target waveforms hybridizing NR waveforms, covering the last approx. 10 orbits up to merger and extending through the postmerger phase, with inspiral waveforms calculated from 30Hz obtained with TEOBResumS. The latter is a state-of-the-art effective-one-body waveform model that blends together tidal and spin effects. We probe that the combination of the PN-based self-spin terms and of the NRTidal description is necessary to obtain minimal mismatches (< 0.01) and phase differences (< 1 rad) with respect to the target waveforms. However, we also discuss possible improvements and drawbacks of the NRTidal approximant in its current form, since we find that it tends to overestimate the tidal interaction with respect to the TEOBResumS model during the inspiral.

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arXiv2018

Parameterized tests of the strong-field dynamics of general relativity using gravitational wave signals from coalescing binary black holes: Fast likelihood calculations and sensitivity of the method

Thanks to the recent discoveries of gravitational wave signals from binary black hole mergers by Advanced Laser Interferometer Gravitational Wave Observatory and Advanced Virgo, the genuinely strong-field dynamics of spacetime can now be probed, allowing for stringent tests of general relativity (GR). One set of tests consists of allowing for parametrized deformations away from GR in the template waveform models and then constraining the size of the deviations, as was done for the detected signals in previous work. In this paper, we construct reduced-order quadratures so as to speed up likelihood calculations for parameter estimation on future events. Next, we explicitly demonstrate the robustness of the parametrized tests by showing that they will correctly indicate consistency with GR if the theory is valid. We also check to what extent deviations from GR can be constrained as information from an increasing number of detections is combined. Finally, we evaluate the sensitivity of the method to possible violations of GR.

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arXiv2016

Effective-one-body waveforms for binary neutron stars using surrogate models

Gravitational-wave observations of binary neutron star systems can provide information about the masses, spins, and structure of neutron stars. However, this requires accurate and computationally efficient waveform models that take <1s to evaluate for use in Bayesian parameter estimation codes that perform 10^7 - 10^8 waveform evaluations. We present a surrogate model of a nonspinning effective-one-body waveform model with l = 2, 3, and 4 tidal multipole moments that reproduces waveforms of binary neutron star numerical simulations up to merger. The surrogate is built from compact sets of effective-one-body waveform amplitude and phase data that each form a reduced basis. We find that 12 amplitude and 7 phase basis elements are sufficient to reconstruct any binary neutron star waveform with a starting frequency of 10Hz. The surrogate has maximum errors of 3.8% in amplitude (0.04% excluding the last 100M before merger) and 0.043 radians in phase. The version implemented in the LIGO Algorithm Library takes ~0.07s to evaluate for a starting frequency of 30Hz and ~0.8s for a starting frequency of 10Hz, resulting in a speed-up factor of ~10^3 - 10^4 relative to the original Matlab code. This allows parameter estimation codes to run in days to weeks rather than years, and we demonstrate this with a Nested Sampling run that recovers the masses and tidal parameters of a simulated binary neutron star system.

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arXiv2015

Testing General Relativity with Present and Future Astrophysical Observations

One century after its formulation, Einstein's general relativity has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in the weak-field regime, and there are theoretical and experimental reasons to believe that general relativity should be modified when gravitational fields are strong and spacetime curvature is large. The best astrophysical laboratories to probe strong-field gravity are black holes and neutron stars, whether isolated or in binary systems. We review the motivations to consider extensions of general relativity. We present a (necessarily incomplete) catalog of modified theories of gravity for which strong-field predictions have been computed and contrasted to Einstein's theory, and we summarize our current understanding of the structure and dynamics of compact objects in these theories. We discuss current bounds on modified gravity from binary pulsar and cosmological observations, and we highlight the potential of future gravitational wave measurements to inform us on the behavior of gravity in the strong-field regime.

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arXiv2015

Constraining the neutron star equation of state with gravitational wave signals from coalescing binary neutron stars

Recently exploratory studies were performed on the possibility of constraining the neutron star equation of state (EOS) using signals from coalescing binary neutron stars, or neutron star-black hole systems, as they will be seen in upcoming advanced gravitational wave detectors such as Advanced LIGO and Advanced Virgo. In particular, it was estimated to what extent the combined information from multiple detections would enable one to distinguish between different equations of state through hypothesis ranking or parameter estimation. Under the assumption of zero neutron star spins both in signals and in template waveforms and considering tidal effects to 1 post-Newtonian (1PN) order, it was found that O(20) sources would suffice to distinguish between a hard, moderate, and soft equation of state. Here we revisit these results, this time including neutron star tidal effects to the highest order currently known, termination of gravitational waveforms at the contact frequency, neutron star spins, and the resulting quadrupole-monopole interaction. We also take the masses of neutron stars in simulated sources to be distributed according to a relatively strongly peaked Gaussian, as hinted at by observations, but without assuming that the data analyst will necessarily have accurate knowledge of this distribution for use as a mass prior. We find that especially the effect of the latter is dramatic, necessitating many more detections to distinguish between different EOS and causing systematic biases in parameter estimation, on top of biases due to imperfect understanding of the signal model pointed out in earlier work. This would get mitigated if reliable prior information about the mass distribution could be folded into the analyses.

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arXiv2014

TIGER: A data analysis pipeline for testing the strong-field dynamics of general relativity with gravitational wave signals from coalescing compact binaries

The direct detection of gravitational waves with upcoming second-generation gravitational wave detectors such as Advanced LIGO and Virgo will allow us to probe the genuinely strong-field dynamics of general relativity (GR) for the first time. We present a data analysis pipeline called TIGER (Test Infrastructure for GEneral Relativity), which is designed to utilize detections of compact binary coalescences to test GR in this regime. TIGER is a model-independent test of GR itself, in that it is not necessary to compare with any specific alternative theory. It performs Bayesian inference on two hypotheses: the GR hypothesis $\mathcal{H}_{\rm GR}$, and $\mathcal{H}_{\rm modGR}$, which states that one or more of the post-Newtonian coefficients in the waveform are not as predicted by GR. By the use of multiple sub-hypotheses of $\mathcal{H}_{\rm modGR}$, in each of which a different number of parameterized deformations of the GR phase are allowed, an arbitrarily large number of 'testing parameters' can be used without having to worry about a model being insufficiently parsimonious if the true number of extra parameters is in fact small. TIGER is well-suited to the regime where most sources have low signal-to-noise ratios, again through the use of these sub-hypotheses. Information from multiple sources can trivially be combined, leading to a stronger test. We focus on binary neutron star coalescences, for which sufficiently accurate waveform models are available that can be generated fast enough on a computer to be fit for use in Bayesian inference. We show that the pipeline is robust against a number of fundamental, astrophysical, and instrumental effects, such as differences between waveform approximants, a limited number of post-Newtonian phase contributions being known, the effects of neutron star spins and tidal deformability on the orbital motion, and instrumental calibration errors.

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arXiv2013

Demonstrating the feasibility of probing the neutron star equation of state with second-generation gravitational wave detectors

Fisher matrix and related studies have suggested that with second-generation gravitational wave detectors, it may be possible to infer the equation of state of neutron stars using tidal effects in binary inspiral. Here we present the first fully Bayesian investigation of this problem. We simulate a realistic data analysis setting by performing a series of numerical experiments of binary neutron star signals hidden in detector noise, assuming the projected final design sensitivity of the Advanced LIGO- Virgo network. With an astrophysical distribution of events (in particular, uniform in co-moving volume), we find that only a few tens of detections will be required to arrive at strong constraints, even for some of the softest equations of state in the literature. Thus, direct gravitational wave detection will provide a unique probe of neutron star structure.

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arXiv2013

Astrophysics, cosmology, and fundamental physics with compact binary coalescence and the Einstein Telescope

The second-generation interferometric gravitational wave detectors currently under construction are expected to make their first detections within this decade. This will firmly establish gravitational wave physics as an empirical science and will open up a new era in astrophysics, cosmology, and fundamental physics. Already with the first detections, we will be able to, among other things, establish the nature of short-hard gamma ray bursts, definitively confirm the existence of black holes, measure the Hubble constant in a completely independent way, and for the first time gain access to the genuinely strong-field dynamics of gravity. Hence it is timely to consider the longer-term future of this new field. The Einstein Telescope (ET) is a concrete conceptual proposal for a third-generation gravitational wave observatory, which will be ~10 times more sensitive in strain than the second-generation detectors. This will give access to sources at cosmological distances, with a correspondingly higher detection rate. I give an overview of the science case for ET, with a focus on what can be learned from signals emitted by coalescing compact binaries. Third-generation observatories will allow us to map the coalescence rate out to redshifts z ~ 3, determine the mass functions of neutron stars and black holes, and perform precision measurements of the neutron star equation of state. ET will enable us to study the large-scale structure and evolution of the Universe without recourse to a cosmic distance ladder. Finally, I discuss how it will allow for high-precision measurements of strong-field, dynamical gravity.

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arXiv2013

Probing dynamical spacetimes with gravitational waves

This decade will see the first direct detections of gravitational waves by observatories such as Advanced LIGO and Virgo. Among the prime sources are coalescences of binary neutron stars and black holes, which are ideal probes of dynamical spacetime. This will herald a new era in the empirical study of gravitation. For the first time, we will have access to the genuinely strong-field dynamics, where low-energy imprints of quantum gravity may well show up. In addition, we will be able to search for effects which might only make their presence known at large distance scales, such as the ones that gravitational waves must traverse in going from source to observer. Finally, coalescing binaries can be used as cosmic distance markers, to study the large-scale structure and evolution of the Universe. With the advanced detector era fast approaching, concrete data analysis algorithms are being developed to look for deviations from general relativity in signals from coalescing binaries, taking into account the noisy detector output as well as the expectation that most sources will be near the threshold of detectability. Similarly, several practical methods have been proposed to use them for cosmology. We explain the state of the art, including the obstacles that still need to be overcome in order to make optimal use of the signals that will be detected. Although the emphasis will be on second-generation observatories, we will also discuss some of the science that could be done with future third-generation ground-based facilities such as Einstein Telescope, as well as with space-based detectors.

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arXiv2012

A Mock Data Challenge for the Einstein Gravitational-Wave Telescope

Einstein Telescope (ET) is conceived to be a third generation gravitational-wave observatory. Its amplitude sensitivity would be a factor ten better than advanced LIGO and Virgo and it could also extend the low-frequency sensitivity down to 1--3 Hz, compared to the 10--20 Hz of advanced detectors. Such an observatory will have the potential to observe a variety of different GW sources, including compact binary systems at cosmological distances. ET's expected reach for binary neutron star (BNS) coalescences is out to redshift $z\simeq 2$ and the rate of detectable BNS coalescences could be as high as one every few tens or hundreds of seconds, each lasting up to several days. %in the sensitive frequency band of ET. With such a signal-rich environment, a key question in data analysis is whether overlapping signals can be discriminated. In this paper we simulate the GW signals from a cosmological population of BNS and ask the following questions: Does this population create a confusion background that limits ET's ability to detect foreground sources? How efficient are current algorithms in discriminating overlapping BNS signals? Is it possible to discern the presence of a population of signals in the data by cross-correlating data from different detectors in the ET observatory? We find that algorithms currently used to analyze LIGO and Virgo data are already powerful enough to detect the sources expected in ET, but new algorithms are required to fully exploit ET data.

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arXiv2012

Effect of calibration errors on Bayesian parameter estimation for gravitational wave signals from inspiral binary systems in the advanced detectors era

By 2015 the advanced versions of the gravitational-wave detectors Virgo and LIGO will be online. They will collect data in coincidence with enough sensitivity to potentially deliver multiple detections of gravitation waves from inspirals of compact-object binaries. This work is focused on understanding the effects introduced by uncertainties in the calibration of the interferometers. We consider plausible calibration errors based on estimates obtained during LIGO's fifth and Virgo's third science runs, which include frequency-dependent amplitude errors of $\sim 10%$ and frequency-dependent phase errors of $\sim 3$ degrees in each instrument. We quantify the consequences of such errors estimating the parameters of inspiraling binaries. We find that the systematics introduced by calibration errors on the inferred values of the chirp mass and mass ratio are smaller than 20% of the statistical measurement uncertainties in parameter estimation for 90% of signals in our mock catalog. Meanwhile, the calibration-induced systematics in the inferred sky location of the signal are smaller than $\sim 50%$ of the statistical uncertainty. We thus conclude that calibration-induced errors at this level are not a significant detriment to accurate parameter estimation.

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