We present results on the search for the coalescence of compact binary mergers using convolutional neural networks and the LIGO/Virgo data, corresponding to the O2 observation period. Two-dimensional images in time and frequency are used as input, and two sets of neural networks are trained separately for low mass (0.2 - 2.0 Msun) and high mass (25 - 100 Msun) compact binary coalescence events. We explored neural networks trained with input information from a single or a pair of interferometers, indicating that the use of information from pairs leads to an improved performance. A scan over the full O2 data set using the convolutional neural networks for detection demonstrates that the performance is compatible with that from canonical pipelines using matched filtering techniques. No additional events with significant signal-to-noise ratio are found in the O2 data.
We summarize the sensitivity achieved by the LIGO and Virgo gravitational wave detectors for low-mass compact binary coalescence (CBC) searches during LIGO's sixth science run and Virgo's second and third science runs. We present strain noise power spectral densities (PSDs) which are representative of the typical performance achieved by the detectors in these science runs. The data presented here and in the accompanying web-accessible data files are intended to be released to the public as a summary of detector performance for low-mass CBC searches during S6 and VSR2-3.
We show that the NANOGrav signal can come from the Higgs field with a noncanonical kinetic term in terms of the scalar induced gravitational waves. The scalar induced gravitational waves generated in our model are also detectable by space-based gravitational wave observatories. Primordial black holes with stellar masses that can explain LIGO-Virgo events are also produced. Therefore, the NANOGrav signal and the BHs in LIGO-Virgo events may both originate from the Higgs field.
We report on a search for gravitational waves from coalescing compact binaries, of total mass between 2 and 35 Msun, using LIGO observations between November 14, 2006 and May 18, 2007. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass. The LIGO cumulative 90%-confidence rate upper limits of the binary coalescence of neutron stars, black holes and black hole-neutron star systems are 1.4x10^-2, 7.3x10^-4 and 3.6x10^-3 yr^-1L_10^-1 respectively, where L_10 is 10^10 times the blue solar luminosity.
The first generation of ground-based interferometric gravitational wave detectors, LIGO, GEO and Virgo, have operated and taken data at their design sensitivities over the last few years. The data has been examined for the presence of gravitational wave signals. Presented here is a comprehensive review of the most significant results. The network of detectors is currently being upgraded and extended, providing a large likelihood for observations. These future prospects will also be discussed.
We report the results of the first search for gravitational waves from compact binary coalescence using data from the LIGO and Virgo detectors. Five months of data were collected during the concurrent S5 (LIGO) and VSR1 (Virgo) science runs. The search focused on signals from binary mergers with a total mass between 2 and 35 Msun. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for non-spinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7x10^-3, 2.2x10^-3 and 4.…
We examine the benefits of performing a joint LIGO--Virgo search for transient signals. We do this by adding burst and inspiral signals to 24 hours of simulated detector data. We find significant advantages to performing a joint coincidence analysis, above either a LIGO only or Virgo only search. These include an increased detection efficiency, at a fixed false alarm rate, to both burst and inspiral events and an ability to reconstruct the sky location of a signal.
Current tests of General Relativity are performed using approximations which neglect a key feature of complete solution of Einstein's theory: higher-order modes. Our analysis will reassess these tests, including these higher-order mode effects. We have chosen to perform inspiral-merger-ringdown consistency tests on the gravitational transients detected by LIGO and Virgo during the observing run O2. We use an approximant which includes all higher modes with $\ell \le 4$ (NRSur7dq2) and then, for the most interesting cases, we repeat the tests involving fits on Numerical Relativity simulations.
We describe the Multi-Band Template Analysis (MBTA) search for gravitational waves signals from coalescences of compact objects in the LIGO-Virgo data, at the time of the third observing run (2019-2020), both for low-latency detections and for offline analysis. Details are given on the architecture and functioning of the pipeline, including transient noise mitigation strategies, parameter space for the searched signals, detection of candidates and evaluation of a false alarm rate associated to them. The performance of the low-latency search is demonstrated based on the LIGO-Virgo third observi…
The LIGO detectors are sensitive to a variety of noise transients of non-astrophysical origin. Instrumental glitches and environmental disturbances increase the false alarm rate in the searches for gravitational waves. Using times already identified when the interferometers produced data of questionable quality, or when the channels that monitor the interferometer indicated non-stationarity, we have developed techniques to safely and effectively veto false triggers from the compact binary coalescences (CBCs) search pipeline.
Formation of primordial black holes from inflationary fluctuations is accompanied by a scalar induced gravitational wave background. We perform a Bayesian search of such background in the data from Advanced LIGO and Virgo's first, second and third observing runs, parametrizing the peak in the curvature power spectrum by a log-normal distribution. The search shows no evidence for such a background. We place 95\% confidence level upper limits on the integrated power of the curvature power spectrum peak which, for a narrow width, reaches down to $0.02$ at $10^{17}\,{\rm Mpc}^{-1}$. The resulting …
The search procedure for burst gravitational waves has been studied using 24 hours of simulated data in a network of three interferometers (Hanford 4-km, Livingston 4-km and Virgo 3-km are the example interferometers). Several methods to detect burst events developed in the LIGO Scientific Collaboration (LSC) and Virgo collaboration have been studied and compared. We have performed coincidence analysis of the triggers obtained in the different interferometers with and without simulated signals added to the data. The benefits of having multiple interferometers of similar sensitivity are demonst…
Sufficient statistics are combinations of data in terms of which the likelihood function can be rewritten without loss of information. Depending on the data volume reduction, the use of sufficient statistics as a preliminary step in a Bayesian analysis can lead to significant increases in efficiency when sampling from posterior distributions of model parameters. Here we show that the frequency integrand of the cross-correlation statistic and its variance are approximate sufficient statistics for ground-based searches for stochastic gravitational-wave backgrounds. The sufficient statistics are …
We present a comparative study of 6 search methods for gravitational wave bursts using simulated LIGO and Virgo noise data. The data's spectra were chosen to follow the design sensitivity of the two 4km LIGO interferometers and the 3km Virgo interferometer. The searches were applied on replicas of the data sets to which 8 different signals were injected. Three figures of merit were employed in this analysis: (a) Receiver Operator Characteristic curves, (b) necessary signal to noise ratios for the searches to achieve 50 percent and 90 percent efficiencies, and (c) variance and bias for the esti…
Presented in this paper is a detailed and direct comparison of the LIGO and Virgo binary neutron star detection pipelines. In order to test the search programs, numerous inspiral signals were added to 24 hours of simulated detector data. The efficiencies of the different pipelines were tested, and found to be comparable. Parameter estimation routines were also tested. We demonstrate that there are definite benefits to be had if LIGO and Virgo conduct a joint coincident analysis; these advantages include increased detection efficiency and the providing of source sky location information.
The origin of the black hole mergers detected by LIGO and Virgo remains an open question. While the unusual mass and spin of a few events constrain their possible astrophysical formation mechanisms, it is difficult to classify the bulk of the observed mergers. Here we consider the distribution of masses and spins in LIGO/Virgo's first and second observing catalogs, and find that for a significant fraction (25%) of these detected events, an AGN-disk origin model is preferred over a parametric mass-spin model fit to the full GWTC-2 merger sample (Bayes factor $\mathcal{B}>10$). We use this to es…
Detector characterization and data quality -- in short "DetChar" -- activities are key to optimize the performance of data-taking periods ("runs") and to turn gravitational-wave (GW) candidates into confirmed events. The LIGO and Virgo DetChar groups are active from the detector to the final analysis and cover various latencies: online first, to tag the data that search pipelines can analyze in real-time; then, the quick vetting (few tens of minutes at most) of the open public alerts targeting the broad astronomer community for follow-up observations; finally, offline work to define the final …
This article reports on a project that is the first step the LIGO Scientific Collaboration and the Virgo Collaboration have taken to prepare for the mutual search for inspiral signals. The project involved comparing the analysis pipelines of the two collaborations on data sets prepared by both sides, containing simulated noise and injected events. The ability of the pipelines to detect the injected events was checked, and a first comparison of how the parameters of the events were recovered has been completed.
Advanced LIGO and Advanced Virgo are expected to make the first direct detections of gravitational waves (GW) in the next several years. Possible types of GW emission include short-duration bursts, signals from the coalescence of compact binaries consisting of neutron stars or black holes, continuous radiation from fast-spinning neutron stars, and stochastic background radiation of a primordial nature or resulting from the superposition of a large number of individually unresolvable sources. We describe the different approaches that have been developed to search for these different types of si…
We present results from an all-sky search for unmodeled gravitational-wave bursts in the data collected by the LIGO, GEO 600 and Virgo detectors between November 2006 and October 2007. The search is performed by three different analysis algorithms over the frequency band 50-6000 Hz. Data are analyzed for times with at least two of the four LIGO-Virgo detectors in coincident operation, with a total live time of 266 days. No events produced by the search algorithms survive the selection cuts. We set a frequentist upper limit on the rate of gravitational-wave bursts impinging on our network of de…
The IceCube neutrino event detected 360 s before the trigger of LIGO/Virgo S190728q is unlikely to be physically associated with the GW event because of an energy budget reason.
Gravitational waves from merging neutron stars are expected to be observed in the next 5 years. We explore the potential impact of matter effects on gravitational waves from merging double neutron-star binaries. If neutron star binaries exist with chirp masses less than roughly 1 solar mass and typical neutron-star radii are larger than roughly 14 km, or if neutron-star radii are larger than 15-16 km for the chirp masses of galactic neutron-star binaries, then matter will have a significant impact on the effectiveness of a point-particle-based search at Advanced LIGO design sensitivity (roughl…
In the first Gravitational-Wave Transient Catalogue of LIGO and Virgo, all events are announced having zero eccentricity. In the present paper, we investigate the performance of SEOBNRE which is a spin-aligned eccentric waveform model in time-domain. By comparing with all the eccentric waveforms in SXS library, we find that the SEOBNRE coincides perfectly with numerical relativity data. Employing the SEOBNRE, we re-estimate the eccentricities of all black hole merger events. We find that most of these events allow a possibility for existence of initial eccentricities at 10 Hz band, but are tot…
The data analysis carried out by the LIGO-Virgo collaboration on gravitational-wave events utilizes nested sampling to compute Bayesian evidences and posterior distributions for inferring the source properties of compact binaries. With poor sampling from the constrained prior, nested sampling algorithms may misbehave and fail to sample the posterior distribution faithfully. Fowlie et al. (2020) outlines a method of validating the performance of nested sampling, or identifying pathologies such as plateaus in the parameter space, using likelihood insertion order statistics. Here, this method is …
We have examined gravitational wave echo signals for nine binary black hole merger events observed by Advanced LIGO and Virgo during the first and second observation runs. To construct an echo template, we consider Kerr spacetime, where the event horizon is replaced by a reflective membrane. We use frequency-dependent reflection rate at the angular potential barrier, which is fitted to the numerical data obtained by solving Teukolsky equations. This reflection rate gives a frequency-dependent transmission rate that is suppressed at lower frequencies in the template. We also take into account t…
We consider the question of cross-correlation measurements using Virgo and the LSC Interferometers (LIGO Livingston, LIGO Hanford, and GEO600) to search for a stochastic gravitational-wave background. We find that inclusion of Virgo into the network will substantially improve the sensitivity to correlations above 200 Hz if all detectors are operating at their design sensitivity. This is illustrated using a simulated isotropic stochastic background signal, generated with an astrophysically-motivated spectrum, injected into 24 hours of simulated noise for the LIGO and Virgo interferometers.
We present a critical reanalysis of the black-hole binary coalescences detected during LIGO's first observing run under different Bayesian prior assumptions. We summarize the main findings of Vitale et al. (2017) and show additional marginalized posterior distributions for some of the binaries' intrinsic parameters.
We explore a method to assess the relative scale of the strain measured in the different detectors of the gravitational-wave network, using binary black hole (BBH) events detected during the third observing run (O3). The number of such signals is becoming sufficiently large to adopt a statistical approach based on the ratio of the signal-to-noise ratio (SNR) of the events between the detectors and the number of observed events in each detector. We demonstrate the principle of the method on simulations of BBH signals and we present its application to published O3 events reported by the Multi-Ba…
The weak equivalence principle (WEP) is the cornerstone of gravitational theories. At the local scale, WEP has been tested to high accuracy by various experiments. On the intergalactic distance scale, WEP could be tested by comparing the arrival time of different messengers emitted from the same source. The gravitational time delay caused by massive galaxies is proportional to $γ+1$, where the parameter $γ$ is unity in general relativity. The values of $γ$ for different massless particles should be different if WEP is violated, i.e., $Δγ$ is used to indicate the deviation from WEP. So far, $|Δ…
We have searched for gravitational waves from coalescing low mass compact binary systems with a total mass between 2 and 35 Msun and a minimum component mass of 1 Msun using data from the first year of the fifth science run (S5) of the three LIGO detectors, operating at design sensitivity. Depending on mass, we are sensitive to coalescences as far as 150 Mpc from the Earth. No gravitational wave signals were observed above the expected background. Assuming a compact binary objects population with a Gaussian mass distribution representing binary neutron star systems, black hole-neutron star bin…
Coalescing compact binaries of neutron stars and/or black holes are considered as one of the most promising sources for Earth based gravitational wave detectors. The LIGO-Virgo joint collaboration's Compact Binary Coalescence (CBC) group is searching for gravitational waves emitted by these astrophysical systems by matched filtering the data against theoretically modeled template waveforms. A variety of waveform template families are employed depending on the mass range probed by the search and the stage of the inspiral phase targeted: restricted post-Newtonian for systems having total mass le…
Gravitational waves would attain birefringence during their propagation from distant sources to the Earth, when the CPT symmetry is broken. If it was sizeable enough, such birefringence could be measured by the Advanced LIGO, Virgo and KAGRA detector network. In this work, we place constraints on the birefringence of gravitational waves with the third observing run of this network, i.e. two catalogues GWTC-2 and GWTC-3. For the dispersion relation $ω^{2}=k^{2}\pm2ζk^{3}$, our analysis shows the up-to-date strictest limit on the CPT-violating parameter, i.e. \textcolor{black}{{$ζ=4.07^{+5.91}_{…
We describe the method used by the Multi-Band Template Analysis (MBTA) pipeline to compute the probability of astrophysical origin, $p_{astro}$, of compact binary coalescence candidates in LIGO-Virgo data from the third observing run (O3). The calculation is performed as part of the offline analysis and is used to characterize candidate events, along with their source classification. The technical details and the implementation are described, as well as the results from the first half of the third observing run (O3a) published in GWTC-2.1. The performance of the method is assessed on injection…
Gravitational wave detection from binary black hole (BBH) inspirals has become routine thanks to the LIGO/Virgo interferometers. The nature of these back holes remains uncertain. We study here the spin distributions of LIGO/Virgo black holes from the first catalogue GWTC-1 and the first four published BBH events from run O3. We compute the Bayes evidence for several independent priors: flat, isotropic, spin-aligned and anti-aligned. We find strong evidence for low spins in all of the cases, and significant evidence for small isotropic spins versus any other distribution. When considered as a h…
Gravitational-wave memory, a strong-field effect of general relativity, manifests itself as a permanent displacement in spacetime. We develop a Bayesian framework to detect gravitational-wave memory with the Advanced LIGO/Virgo detector network. We apply this algorithm on the ten binary black hole mergers in LIGO/Virgo's first transient gravitational-wave catalog. We find no evidence of memory, which is consistent with expectations. In order to estimate when memory will be detected, we use the best current population estimates to construct a realistic sample of binary black hole observations f…
A discovery of gravitational waves from binary black holes raises a possibility that measurements of them can provide strict tests of CPT invariance in gravitational waves. When CPT violation exists, if any, gravitational waves with different circular polarizations could gain a slight difference in propagating speeds. Hence, the birefringence of gravitational waves is induced and there should be a rotation of plus and cross modes. For CPT-violating dispersion relation ${ω^{2}=k^{2}}$ ${\pm 2ζk^{3}}$, where a sign ${\pm}$ denotes different circular polarizations, we find no substantial deviatio…
A stochastic gravitational wave background is expected to emerge from the superposition of numerous gravitational wave sources of both astrophysical and cosmological origin. A number of cosmological models can have a parity violation, resulting in the generation of circularly polarised gravitational waves. We present a method to search for parity violation in the gravitational wave data. We first apply this method to the most recent, third, LIGO-Virgo observing run. We then investigate the constraining power of future A+ LIGO-Virgo detectors, including KAGRA to the network, for a gravitational…
On correlated noise in the LIGO-Virgo network: a test of the stochastic gravitational-wave background hypothesis
Instituto de Física, Universidade de Brasília（巴西利亚大学物理研究所）；Canadian Quantum Research Center（加拿大量子研究中心）；Instituto Federal do Tocantins（托坎廷斯联邦学院）；Universidade Federal do Norte do Tocantins, Centro de Ciências Integradas（托坎廷斯北部联邦大学综合科学中心）
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 …
We describe the methodology and novel techniques used to construct a set of waveforms, or template bank, applicable to searches for compact binary coalescences in Advanced LIGO's second observing run. This template bank is suitable for observing systems composed of two neutron stars, two black holes, or a neutron star and a black hole. The Post-Newtonian formulation is used to model waveforms with total mass less than 4 $M_{\odot}$ and the most recent effective-one-body model, calibrated to numerical relativity to include the merger and ringdown, is used for total masses greater than 4 $M_{\od…
The Advanced LIGO and Advanced Virgo detectors have commenced observations. Gravitational waves from the merger of binary black hole systems and a binary neutron star system have been observed. A major goal for LIGO and Virgo is to detect or set limits on a stochastic background of gravitational waves. A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved cosmological and/or astrophysical sources. A cosmologically produced background would carry unique signatures from the earliest epochs in the evolution of the Universe. Simila…
General relativity predicts mass and spin growth of an inspiralling black hole due to an energy-momentum flux flowing through the black-hole horizon. The leading-order terms of this horizon flux introduce 2.5 and 3.5 post-Newtonian corrections to inspiral motions of binary black holes. The corrections may be measurable by gravitational waves detectors. Since the proper improvements to general relativity is still a mystery, it is possible that the true modified gravity theory introduces negligible direct corrections to the geodesics of test masses, while near horizon corrections are observable.…
We summarize the four tests of general relativity carried out using the ten binary black hole signals detected by Advanced LIGO and Advanced Virgo and included in their first catalog, GWTC-1. These events provide unprecedented opportunities for testing the predictions of general relativity for the gravitational waveforms from these highly dynamical, strong-field events. The first two tests check the consistency of the residuals with noise and the consistency of the low- and high-frequency parts of the signal. The other two tests check that parameterized deviations in the waveform model---inclu…
Long-lived gravitational wave (GW) transients have received interest in the last decade, as the sensitivity of LIGO and Virgo increases. Such signals, lasting between 10 and 1000s, can come from a variety of sources, including accretion disk instabilities around black holes, binary neutron stars post-merger, core-collapse supernovae, non-axisymmetric deformations in isolated neutron stars, and magnetar giant flares. Given the large parameter space and the lack of precisely modeled waveforms, searches must rely on robust detection algorithms, which make few or no assumptions on the nature of th…
Causality and the generalized laws of black hole thermodynamics imply a bound, known as the \textit{Bekenstein--Hod universal bound}, on the information emission rate of a perturbed system. Using a time-domain ringdown analysis, we investigate whether remnant black holes produced by the coalescences observed by Advanced LIGO and Advanced Virgo obey this bound. We find that the bound is verified by the astrophysical black hole population with $94\%$ probability, providing a first confirmation of the Bekenstein--Hod bound from black hole systems.
The LIGO Scientific Collaboration and Virgo Collaboration have carried out joint searches in LIGO and Virgo data for periodic continuous gravitational waves. These analyses range from targeted searches for gravitational-wave signals from known pulsars, for which precise ephemerides from radio or X-ray observations are used in matched filters, to all-sky searches for unknown neutron stars, including stars in binary systems. Between these extremes lie directed searches for known stars of unknown spin frequency or for new unknown sources at specific locations, such as near the galactic center or …
The LIGO and Virgo detectors are sensitive to a variety of noise sources, such as instrumental artifacts and environmental disturbances. The Stochastic Transient Analysis Multi-detector Pipeline (STAMP) has been developed to search for long-duration (t$\gtrsim$1s) gravitational-wave (GW) signals. This pipeline can also be used to identify environmental noise transients. Here we present an algorithm to determine when long-duration noise sources couple into the interferometers, as well as identify what these noise sources are. We analyze the cross-power between a GW strain channel and an environ…
An important goal for LIGO (the Laser Interferometer Gravitational-Wave Observatory) and Virgo is to find periodic sources of gravitational waves. The LIGO and Virgo detectors are sensitive to a variety of noise of non-astrophysical origin, such as instrumental artifacts and environmental disturbances. These artifacts make it difficult to know when a signal is due to a gravitational wave or noise. A continuous wave search algorithm, Fscan, and the calculation of the coherence between the gravitational wave channels and auxiliary channels has been developed to identify the source of noise lines…
After their successful first observing run (September 12, 2015 - January 12, 2016), the Advanced LIGO detectors were upgraded to increase their sensitivity for the second observing run (November 30, 2016 - August 26, 2017). The Advanced Virgo detector joined the second observing run on August 1, 2017. We discuss the updates that happened during this period in the GstLAL-based inspiral pipeline, which is used to detect gravitational waves from the coalescence of compact binaries both in low latency and an offline configuration. These updates include deployment of a zero-latency whitening filter…
Search for Peak Structures in the Stochastic Gravitational-Wave Background in LIGO-Virgo-KAGRA O1-O4a Datasets
Institut de Física d’Altes Energies (IFAE)（高等能源物理研究所）；Barcelona Institute of Science and Technology (BIST)（巴塞罗那科学与技术研究院）；Universitat Autònoma de Barcelona (UAB)（巴塞罗那自治大学）；Catalan Institution for Research and Advanced Studies (ICREA)（加泰罗尼亚研究高级机构）
We demonstrate a single-parameter route for reproducing higher mass objects as observed in the LIGO--Virgo mass distribution, using only the isolated binary stellar evolution channel. This single parameter encodes the cosmological mass growth of compact stellar remnants that exceed the Tolman-Oppenheimer-Volkoff limit. Cosmological mass growth appears in known solutions to General Relativity with cosmological boundary conditions. We consider the possibility of solutions with cosmological boundary conditions, which reduce to Kerr on timescales short compared to the Hubble time. We discuss compl…
This brief report describes the search for gravitational-wave inspiral signals from short gamma-ray bursts. Since these events are probably created by the merger of two compact objects, a targeted search with a lower threshold can be made. The data around 22 short gamma-ray bursts have been analyzed.
Short Gamma Ray Bursts (SGRB) are believed to originate from the merger of two compact objects. If this scenario is correct, SGRB will be accompanied by the emission of strong gravitational waves, detectable by current or planned GW detectors, such as LIGO and Virgo. No detection of a gravitational wave has been made up to date. In this paper I will use a set of SGRB with observed redshifts to fit a model describing the cumulative number of SGRB as a function of redshift, to determine the rate of such merger events in the nearby universe. These estimations will be used to make probability stat…
We show that if the new physics beyond the Standard Model is associated with a first-order phase transition around $10^7-10^8$ GeV, the energy density stored in the resulting stochastic gravitational waves and the corresponding peak frequency are within the projected final sensitivity of the advanced LIGO/VIRGO detectors. We discuss some possible new physics scenarios that could arise at such energies, and in particular, the consequences for Peccei-Quinn and supersymmetry breaking scales.
