Virgo detector characterization and data quality: tools

Detector characterization and data quality studies—collectively referred to as DetChar activities in this article—are paramount to the scientific exploitation of the joint dataset collected by the LIGO-Virgo-KAGRA global network of ground-based gravitational-wave (GW) detectors. They take place during each phase of the operation of the instruments (upgrade, tuning and optimization, data taking), are required at all steps of the dataflow (from data acquisition to the final list of GW events) and operate at various latencies (from near real-time to vet the public alerts to offline analyses). This work requires a wide set of tools which have been developed over the years to fulfill the requirements of the various DetChar studies: data access and bookkeeping; global monitoring of the instruments and of the different steps of the data processing; studies of the global properties of the noise at the detector outputs; identification and follow-up of noise peculiar features (whether they be transient or continuously present in the data); quick processing of the public alerts. The present article reviews all the tools used by the Virgo DetChar group during the third LIGO-Virgo Observation Run (O3, from April 2019 to March 2020), mainly to analyze the Virgo data acquired at EGO. Concurrently, a companion article focuses on the results achieved by the DetChar group during the O3 run using these tools

Virgo Detector Characterization and Data Quality: tools

Detector characterization and data quality studies -- collectively referred to as {\em DetChar} activities in this article -- are paramount to the scientific exploitation of the joint dataset collected by the LIGO-Virgo-KAGRA global network of ground-based gravitational-wave (GW) detectors. They take place during each phase of the operation of the instruments (upgrade, tuning and optimization, data taking), are required at all steps of the dataflow (from data acquisition to the final list of GW events) and operate at various latencies (from near real-time to vet the public alerts to offline analyses). This work requires a wide set of tools which have been developed over the years to fulfill the requirements of the various DetChar studies: data access and bookkeeping; global monitoring of the instruments and of the different steps of the data processing; studies of the global properties of the noise at the detector outputs; identification and follow-up of noise peculiar features (whether they be transient or continuously present in the data); quick processing of the public alerts. The present article reviews all the tools used by the Virgo DetChar group during the third LIGO-Virgo Observation Run (O3, from April 2019 to March 2020), mainly to analyse the Virgo data acquired at EGO. Concurrently, a companion article focuses on the results achieved by the DetChar group during the O3 run using these tools.Comment: 44 pages, 16 figures. To be submitted to Class. and Quantum Grav. This is the "Tools" part of preprint arXiv:2205.01555 [gr-qc] which has been split into two companion articles: one about the tools and methods, the other about the analyses of the O3 Virgo dat

Magnetorotational collapse of very massive stars to black holes in full general relativity

We perform axisymmetric simulations of the magnetorotational collapse of very massive stars in full general relativity. Our simulations are applicable to the collapse of supermassive stars (M > 10^3M_sun) and to very massive Pop III stars. We model our initial configurations by n=3 polytropes. The ratio of magnetic to rotational kinetic energy in these configurations is chosen to be small (1% and 10%). We find that such magnetic fields do not affect the initial collapse significantly. The core collapses to a black hole, after which black hole excision is employed to continue the evolution long enough for the hole to reach a quasi-stationary state. We find that the black hole mass is M_h = 0.95M and its spin parameter is J_h/M_h^2 = 0.7, with the remaining matter forming a torus around the black hole. We freeze the spacetime metric ("Cowling approximation") and continue to follow the evolution of the torus after the black hole has relaxed to quasi-stationary equilibrium. In the absence of magnetic fields, the torus settles down following ejection of a small amount of matter due to shock heating. When magnetic fields are present, the field lines gradually collimate along the hole's rotation axis. MHD shocks and the MRI generate MHD turbulence in the torus and stochastic accretion onto the central black hole. When the magnetic field is strong, a wind is generated in the torus, and the torus undergoes radial oscillations that drive episodic accretion onto the hole. These oscillations produce long-wavelength gravitational waves potentially detectable by LISA. The final state of the magnetorotational collapse always consists of a central black hole surrounded by a collimated magnetic field and a hot, thick accretion torus. This system is a viable candidate for the central engine of a long-soft gamma-ray burst.Comment: 17 pages, 13 figures, replaced with the published versio

PROBING FUNDAMENTAL PHYSICS WITH GRAVITATIONAL WAVES FROM INSPIRALING BINARY SYSTEMS

The mergers of black holes and/or neutron stars in binary systems produce the most extreme gravitational environments in the local universe. The first direct detections of gravitational waves by Advanced LIGO and Virgo provide unprecedented observational access to the highly dynamical, strong-curvature regime of gravity. These measurements allow us to test Einstein’s theory of General Relativity in this extreme regime. This thesis examines how the gravitational-wave signal produced during the inspiral—the earliest phase of a binary’s coalescence—can better inform our understanding of the fundamental nature of gravity. My work addressing this topic is comprised of two major components. First, I examine the behavior of binary black-hole and neutron-star systems in various possible extensions of General Relativity, constructing analytic models of their orbital motion and gravitational waveform—their gravitational-wave signature—during their inspiral. The majority of alternative theories I consider modify General Relativity by introducing a new scalar component of gravity. In many of these theories, standard perturbative techniques are used to model the inspiral of binary systems. However, I also examine in depth the non-perturbative phenomenon of scalarization for which such methods fail. I show that this phenomenon occurs due to a second-order phase transition in the strong-gravity regime and develop an analytic framework to model the effect across a range of alternative theories of gravity. The other component of this thesis is the development of a statistical infrastructure suitable for testing General Relativity using gravitational-wave observations. I adopt a more flexible and modular approach than existing alternatives, allowing this infrastructure to be immediately applied with a wide range of waveform models. In work done in conjunction with the LIGO Scientific and Virgo Collaborations, I use this statistical framework to place bounds on phenomenological deviations from General Relativity using the binary black-hole and neutron-star events detected during LIGO’s first and second observing runs—no evidence for deviations from Relativity is found. These two research directions outlined above are complementary; the type of statistical inference discussed here requires models for the gravitational-wave signal produced by inspiraling systems that allow for deviations from General Relativity, and the analytic models I construct are suitable for this task. In this thesis, I carry out the complete procedure of building and employing analytic models of gravitational waveforms to place constraints on specific alternative theories of gravity with observations by LIGO and Virgo

Hot QCD Phase Diagram From Holographic Einstein-Maxwell-Dilaton Models

In this review, we provide an up-to-date account of quantitative holographic descriptions of the strongly coupled quark-gluon plasma (QGP) produced in heavy-ion collisions, based on the class of gauge-gravity Einstein-Maxwell-Dilaton (EMD) models. Holography is employed to tentatively map the QCD phase diagram at finite temperature onto a dual theory of charged, asymptotically AdS black holes in 5D. With a quantitative focus on the hot QCD phase diagram, the EMD models reviewed are adjusted to describe lattice results for the finite-temperature QCD equation of state, with 2+1 flavors and physical quark masses, at zero chemical potential and vanishing electromagnetic fields. The predictive power of EMD models is tested by quantitatively comparing their predictions for the hot QCD equation of state at nonzero baryon density and the corresponding state-of-the-art lattice QCD results. The shear and bulk viscosities predicted by these EMD models are also compared to the corresponding profiles favored by the latest phenomenological multistage models describing different heavy-ion data. We report preliminary results from a Bayesian analysis which provide systematic evidence that lattice results at finite temperature and zero baryon density strongly constrains the free parameters of EMD models. Remarkably, the set of parameters constrained by lattice results at zero chemical potential produces EMD models in quantitative agreement with lattice QCD results also at finite baryon density. We also review results for equilibrium and transport properties from anisotropic EMD models, describing the QGP at finite temperatures and magnetic fields. Finally, we provide a critical assessment of the main limitations and drawbacks of the holographic models reviewed in the present work, and point out some perspectives we believe are of fundamental importance for future developments.Comment: Invited review, 73 pages, 14 figure

Virgo Detector Characterization and Data Quality during the O3 run

The Advanced Virgo detector has contributed with its data to the rapid growth of the number of detected gravitational-wave signals in the past few years, alongside the two LIGO instruments. First, during the last month of the Observation Run 2 (O2) in August 2017 (with, most notably, the compact binary mergers GW170814 and GW170817) and then during the full Observation Run 3 (O3): an 11 months data taking period, between April 2019 and March 2020, that led to the addition of about 80 events to the catalog of transient gravitational-wave sources maintained by LIGO, Virgo and KAGRA. These discoveries and the manifold exploitation of the detected waveforms require an accurate characterization of the quality of the data, such as continuous study and monitoring of the detector noise. These activities, collectively named {\em detector characterization} or {\em DetChar}, span the whole workflow of the Virgo data, from the instrument front-end to the final analysis. They are described in details in the following article, with a focus on the associated tools, the results achieved by the Virgo DetChar group during the O3 run and the main prospects for future data-taking periods with an improved detector.Comment: 86 pages, 33 figures. This paper has been divided into two articles which supercede it and have been posted to arXiv on October 2022. Please use these new preprints as references: arXiv:2210.15634 (tools and methods) and arXiv:2210.15633 (results from the O3 run

Virgo detector characterization and data quality: results from the O3 run

The Advanced Virgo detector has contributed with its data to the rapid growth of the number of detected GW signals in the past few years, alongside the two Advanced LIGO instruments. First during the last month of the Observation Run 2 (O2) in August 2017 (with, most notably, the compact binary mergers GW170814 and GW170817), and then during the full Observation Run 3 (O3): an 11 months data taking period, between April 2019 and March 2020, that led to the addition of 79 events to the catalog of transient GW sources maintained by LIGO, Virgo and now KAGRA. These discoveries and the manifold exploitation of the detected waveforms benefit from an accurate characterization of the quality of the data, such as continuous study and monitoring of the detector noise sources. These activities, collectively named detector characterization and data quality or DetChar, span the whole workflow of the Virgo data, from the instrument front-end hardware to the final analyses. They are described in detail in the following article, with a focus on the results achieved by the Virgo DetChar group during the O3 run. Concurrently, a companion article describes the tools that have been used by the Virgo DetChar group to perform this work

Analytical modeling of compact binaries in general relativity and modified gravity theories

Gravitational-wave (GW) signals from the coalescence of almost a hundred binary systems have been detected over the past few years. These observations have improved our understanding of binary black holes and neutron stars, their properties, and astrophysical formation channels. GWs also probe gravity in the nonlinear, strong-field regime, thus allowing us to search for, or constrain, deviations from general relativity. The focus of this dissertation is improving the analytical description of binary dynamics, which is important for producing accurate waveform models that can be used in searching for GW signals, inferring their parameters, and testing gravity. The research presented here can be divided into three complementary parts: 1) extending the post-Newtonian (PN) approximation for spinning binaries to higher orders, 2) improving effective-one-body (EOB) waveform models, and 3) identifying some signatures of modified gravity theories in waveforms. The PN approximation, valid for slow motion and weak gravitational field, is widely used to model the dynamics of comparable-mass binaries, which are the main GW sources for ground-based detectors. We derive PN results for spinning binaries at the third- and fourth-subleading PN orders for the spin-orbit coupling, and at the third-subleading order for the spin(1)-spin(2) coupling. We adopt an approach that combines several analytical approximation methods to obtain PN results valid for arbitrary mass ratios from gravitational self-force results at first order in the mass ratio. This is possible due to the simple mass dependence of the scattering angle in the post-Minkowskian approximation (weak field but arbitrary velocities). The EOB formalism produces accurate waveforms by combining analytical results for the binary dynamics with numerical relativity information, while recovering the strong-field test-body limit. To improve EOB models, we include spin-precession effects in the Hamiltonian up to the fourth PN order, and extend the radiation-reaction force and waveform to eccentric orbits. We also assess the accuracy of post-Minkowskian results, for both bound and scattering orbits, and incorporate them in EOB Hamiltonians. In the context of modified gravity theories, we derive the conservative and dissipative dynamics in Einstein-Maxwell-dilaton theory at the next-to-leading PN order, and compute the Fourier-domain gravitational waveform. We also develop a theory-agnostic effective-field-theory approach for describing spontaneous and dynamical scalarization: non-perturbative phenomena in which compact objects can undergo a phase transition and acquire scalar charge. We apply this approach to binary black holes in Einstein-Maxwell-scalar theory using a quasi-stationary approximation, then extend it to account for the dynamical evolution of the scalar charge, and apply it to binary neutron stars in a class of scalar-tensor theories. Improving waveform models is important for current-generation GW detectors and necessary for future detectors, such as LISA, the Einstein telescope, and Cosmic Explorer. The results obtained in this work are important steps towards that goal