Compact Objects in the Universe

Preface
Contents
Modifications of General Relativity: Scalar Tensor Theories
Exact Black Hole Solutions in Higher Order Scalar Tensor Theories
	1 Black Holes and Scalar Tensor Theories
	2 Horndeski and Beyond
		2.1 Horndeski Theories
		2.2 Degenerate Higher-Order Scalar-Tensor (DHOST) Theories
	3 Stealth Black Holes and Their Disformal and Conformal Transformations
		3.1 Generic Stealth Schwarzschild in Horndeski Theories
		3.2 A Stealth Kerr Black Hole in a GR Like DHOST Theory
		3.3 Disformal Kerr Metric
		3.4 Conformal Kerr Metric: Cosmological Black Holes
	4 Black Holes Beyond Ricci Flat Metrics
		4.1 Parity and Shift-Symmetric Theories
		4.2 Non-parity Symmetric Theories
	5 Summary
	References
Compact Objects in EsGB Theory  and Beyond
	1 Introduction
	2 Compact Objects in GR and Einstein-Scalar Theory
		2.1 Black Holes
		2.2 Wormholes
		2.3  Particle-Like Solutions
	3 The Einstein-Scalar-GB Theory
		3.1 Black-Hole Solutions in Einstein-Scalar-GB Theory
		3.2 Wormholes in Einstein-Scalar-GB Theory
		3.3 Particle-Like Solutions in Einstein-Scalar-GB Theory
	4 Compact Objects in (Beyond) Horndeski Theory
	5 Conclusions
	References
Dynamics of Scalarization
	1 Introduction
	2 Scalar-Gauss–Bonnet Gravity—Field Equations and Time Evolution
		2.1 Scalar Field Evolution in Decoupling Limit Approximation
		2.2 Field Equations in Spherical Symmetry
		2.3 Mechanisms of Scalarization
	3 Scalarization of Isolated Compact Objects
		3.1 Scalar Field Dynamics in the Decoupling Limit Approximation
		3.2 Scalar Field Evolution on the Background of a Neutron Star
		3.3 Beyond Decoupling Limit Approximation
	4 Conclusion
	References
EFT Approach to Black Hole Scalarization and Its Compatibility with Cosmic Evolution
	1 Introduction
	2 The Model and Black Hole Scalarization
	3 Perturbations on a FLRW Background
	4 General Relativity as a Cosmic Attractor
	5 Discussion and Conclusions
	References
Conformal Renormalization and Energy Functionals in Anti-De Sitter Gravity
	1 Introduction
	2 Kounterterms in AdS Gravity
	3 Counterterms Versus Kounterterms: A Comparison
	4 Beyond Kounterterms: Conformal Renormalization
	5 Energy Functionals from Conformal Gravity in Four Dimensions
	6 Conclusions
	References
Black Hole Spectroscopy
Black-Hole Spectroscopy: Quasinormal Modes, Ringdown Stability and the Pseudospectrum
	1 Introduction
	2 Black-Hole Perturbation Theory and Quasinormal Modes
		2.1 Quasinormal Mode Detection Status
	3 Early Evidence of a Spectral Instability
	4 The Need for Non-modal Tools: The Pseudospectrum
		4.1 The Mathematical Notion of the Pseudospectrum
		4.2 Hydrodynamics and the Pseudospectrum
		4.3 Black Holes and Their Pseudospectrum in a Nutshell
		4.4 A Pseudospectrum Calculator Primer
	5 Pseudospectrum of Black Holes
		5.1 Pöschl-Teller Potential: A Toy Model
		5.2 Schwarzschild Black Holes
		5.3 Reissner-Nordström Black Holes
	6 Pseudospectrum of Horizonless Exotic Compact Objects
		6.1 Spherically-Symmetric Horizonless Compact Objects: A Simplistic Approach
		6.2 Pseudospectrum of Horizonless Objects with a Pöschl-Teller Potential
		6.3 Pseudospectrum of Horizonless Compact Objects
	7 Destabilizing the Fundamental Quasinormal Mode
	8 Destabilized Fundamental Mode Detection in Ringdown Signals
		8.1 Ringdown Waveform Stability
		8.2 Implications on Black-Hole Spectroscopy
	9 Conclusions and Outlook
	References
WKB Method and Quasinormal Modes of String-Theoretical D-Dimensional Black Holes
	1 Introduction and Summary
	2 Quasinormal Modes
		2.1 Dissipative Systems and Quasinormal Modes
		2.2 Quasinormal Modes of Black Holes
	3 WKB Theory: A Review
		3.1 Defining Purpose and Schrödinger Like Equations
		3.2 Analytic Continuation and Stokes Lines
	4 A String-Corrected Black Hole and Its Perturbations
		4.1 Physical Origin
		4.2 The Metric
		4.3 Gravitational Perturbations and Quasinormal Modes
	5 Quasinormal Modes in the Eikonal Limit
		5.1 Definition and Analysis of upper QQ
		5.2 WKB Approximation
		5.3 Quasinormal Frequencies Computation
	6 Quasinormal Modes in the Asymptotic Limit
		6.1 Variable Change and Perturbation Theory
		6.2 WKB Theory Set up
		6.3 Stokes Lines Topology
		6.4 Boundary Conditions
		6.5 The Monodromy Method
		6.6 The Big Contour
		6.7 The Small Contour
		6.8 Equating Monodromies: The Final Result
	References
Observational Signals of Compact Objects
Spacetime Geometry of Rotating Boson Stars and KBHsSH
	1 Introduction
	2 Theory
		2.1 Action and Equations of Motion
		2.2 Charges
		2.3 Scalar Field Ansatz
		2.4 Note on Self-interaction
	3 Rotating Boson Stars
		3.1 Metric Ansatz and Boundary Conditions
		3.2 Charges
		3.3 Fluid Description and Co-moving Frame
	4 KBHsSH
		4.1 Metric Ansatz and Boundary Conditions
		4.2 Charges
		4.3 Domain of Existence
	5 Equatorial Circular Orbits
		5.1 Static Ring
		5.2 Degenerate Prograde Stable
		5.3 Discontinuous Prograde Stable
		5.4 Discontinuous Circular Orbits
	6 Conclusions
	References
Seven Years of LIGO-Virgo Science
	1 Signal and Noises
		1.1 Thermal Noise
		1.2 Seismic Noise
		1.3 Gravity Gradient Noise
		1.4 Signals
	2 The First Discoveries
		2.1 Localization
		2.2 GW170817
	3 O3 Run and Beyond
		3.1 Tests of General Relativity
		3.2 ``Exceptional\'\' Events
		3.3 Other Searches
	4 Conclusions
	References
Astrophysics of Radio Sources: Analysis of 21cm Post-reionization Signals and Modeling of FRBs as PBHs with Magnetic Fields
	1 Introduction
	2 Extracting HI Information from Sky Maps
		2.1 Caracterizing the 21cm Post-reionization Signals
		2.2 Foreground Signals
		2.3 Modeling the Foreground Removal Process
		2.4 Statistical Estimation of the 21cm Signals
	3 Bispectrum in 21-cm Intensity Mapping
		3.1 Bispectrum Patterns and Foreground Residues
	4 Primordial Black Holes with Magnetic Fields as a Candidate for Fast Radio Bursts
	5 Magnetized Space Times
	References
BINGO-ABDUS: A Radiotelescope to Unveil the Dark Sector of the Universe
	1 Introduction
	2 The BINGO Project
		2.1 Scientific Organization
	3 The ABDUS Project—Advanced Bingo Dark Universe Studies
	4 Other Similar Projects
	References
Gravitational Wave Astronomy
Machine Learning Applications  in Gravitational Wave Astronomy
	1 Introduction
	2 ANN-Accelerated Surrogate Models
		2.1 Constructing a Surrogate Model
		2.2 Accelerating the Surrogate Model Using ANNs
	3 Efficient Surrogate Models Using Autoencoders
	4 GW Detection with Deep Residual Networks
		4.1 Training and Test Datasets
		4.2 Deep Residual Networks
		4.3 Detection of BBH Injections in Real Noise
	5 ANN Surrogate Models of Neutron Star Mass-Radius Relations in Alternative Theories of Gravity
	6 Training and Testing
		6.1 Speed-Up
	7 Conclusions
	References
Features in the Inflaton Potential and the Spectrum of Cosmological Perturbations
	1 Introduction
	2 Beyond Slow-Roll Single-Field Inflation
		2.1 Amplification
		2.2 Oscillatory Patterns
		2.3 Step-Like Transitions Versus Approximate Inflection Points
	3 Turns Without Slow-Roll in Two-Field Inflation
		3.1 Background and Perturbations Evolution
		3.2 Enhancement
		3.3 Describing Turns in Field Space
		3.4 The Quantitative Features of the Evolution
	4 Inflationary Models with Special Features
		4.1 Step-Like Features in the Inflaton Potential
		4.2 Approximate Inflection-Point Inflationary Models
	5 Secondary GWs
		5.1 GWs in Perturbation Theory
		5.2 GWs Beyond Perturbation Theory and During EMD
	6 Conclusions
	References