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Scott Hughes (Massachusetts Institute of Technology)11/09/2023, 09:30
Since 2015’s celebrated first detection of gravitational waves from merging black holes, detectors have measured waves from nearly a hundred different events. Many current detectors are being upgraded, improving their sensitivity and broadening their sensitive wave bands; future detectors are planned which will likewise have wider bands and deeper sensitivity. These future instruments will be...
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Adam Pound11/09/2023, 10:30
As gravitational-wave detectors become more sensitive to lower frequencies, they will increasingly detect binaries with smaller mass ratios, larger spins, and higher eccentricities. In this talk I describe how gravitational self-force theory, when combined with a method of multiscale expansions, provides an ideal framework for modelling these systems. The framework proceeds from first...
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Roy Maartens11/09/2023, 12:00
Tensions in the observed values of the Hubble constant and other key
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parameters of the concordance model of cosmology may indicate problems in
the model itself. This motivates further independent tests of the model. I
will describe a test of a key foundation of the concordance model - the
Cosmological Principle. According to the Cosmological Principle, the
Universe should be statistically... -
Vojtěch Witzany11/09/2023, 15:00
As the reach and sensitivity of gravitational-wave detectors continues to grow, so do the requirements on our understanding of the evolution of compact binaries. When the components of the binary spin at general inclinations, there is, in principle, a sufficient number of degrees of freedom to break integrability of the evolution. However, layer after layer various integrable structures appear...
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Amare Abebe11/09/2023, 15:30
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Che-Yu Chen (iTHEMS, RIKEN)11/09/2023, 15:30
According to General Relativity, an isolated black hole in vacuum shall be described by the Kerr metric, whose geodesic equations are integrable. The violation of integrability leads to chaos for particles moving around the black hole. This chaotic dynamics could leave imprints on the associated gravitational waveform and could be tested with upcoming observations. In this talk, we discuss the...
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Krinio Marouda (CENTRA, Instituto Superior Técnico)11/09/2023, 15:50
It has been thirty years since the breakthrough paper of M. Choptuik on critical phenomena in the gravitational collapse of a real massless scalar field in spherical symmetry. This celebrated paper led to a rich exploration of different extreme spacetimes in numerical relativity in the years following its publication. Those numerical studies persist in questioning the weak cosmic censorship...
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Dr Kyriakos Destounis (Sapienza University of Rome)11/09/2023, 15:50
The historic detection of gravitational waves paved the way for precision gravitational-wave astrophysics to blossom at unprecedented proportions. In this talk, I will focus on extreme-mass-ratio inspirals (EMRIs) that consist of a primary supermassive compact object, and a stellar-mass secondary companion. Even though we are currently performing pertinent tests on order to characterize the...
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Giulia Ventagli (CEICO, Institute of Physics of the Czech Academy of Sciences)11/09/2023, 16:10
Spontaneous scalarization of neutron stars has been extensively studied in the Damour and Esposito-Farèse model, in which a scalar field couples to the Ricci scalar or, equivalently, to the trace of the energy-momentum tensor. However, scalarization of both black holes and neutron stars may also be triggered by a coupling of the scalar field to the Gauss-Bonnet invariant. The case of the...
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Areti Eleni11/09/2023, 16:10
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Alex Giacomini11/09/2023, 17:00
In this talk we perform a systematic investigation of all possible solutions with static compact extra dimensions and expanding three-dimensional subspace. We will consider extra-dimensional subspace to be constant-curvature manifold with both signs of spatial curvature. We provide a scheme how to build solutions in all possible number of extra dimensions and perform stability analysis for the...
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Viola De Renzis (University of Milano-Bicocca)11/09/2023, 17:00
Black-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti-) aligned spins. Among these, binaries in the up–down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. The occurrence of the up–down instability leads to...
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Dr Samuel Upton (Astronomical Institute of the Czech Academy of Sciences)11/09/2023, 17:20
Gravitational self-force theory is the primary way of modelling extreme-mass-ratio inspirals (EMRIs). One difficulty that appears in second-order self-force calculations is the strong divergence at the worldline of the small object, which causes both numerical and analytical issues. Previous work [Phys. Rev. D 95, 104056 (2017); ibid. 103, 124016 (2021)] demonstrated that this could be...
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Andreas Pithis11/09/2023, 17:20
The Barrett-Crane (BC) spin foam and GFT model is a state-sum model which provides a tentative quantization of first order Lorentzian Palatini gravity written as a constrained BF-theory. It is conjectured that this model gives rise to continuum spacetime with General Relativity as an effective description for the dynamics at criticality via phase transition. In this talk, we discuss how phase...
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Viktor Skoupý11/09/2023, 17:40
This work provides gravitational wave energy and angular momentum asymptotic fluxes from a spinning body moving on generic orbits in a Kerr spacetime up to linear in spin approximation. To achieve this, we have developed a new frequency domain Teukolsky equation solver that calculates asymptotic amplitudes from generic orbits of spinning bodies with their spin aligned with the total orbital...
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Angelica Albertini11/09/2023, 18:00
I will present a waveform model for the inspiral of extreme-mass-ratio black hole binaries based on the effective-one-body approach to the two-body problem in general relativity. By means of a gauge-invariant analysis, I will show the agreement of the model with second-order gravitational self-force results for quasi-circular nonspinning binaries. I will then briefly discuss the work in...
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Lukáš Polcar (Charles University)11/09/2023, 18:20
Action-angle (AA) coordinates are commonly used in theoretical description of extreme mass ratio inspirals (EMRI), as they are naturally associated with the two dynamical timescales present in EMRI. However the AA coordinates are rarely used in practical calculations. In our work we implemented analytic methods of canonical perturbation theory to transform geodesic Hamiltonian into AA...
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Stefanos Aretakis12/09/2023, 09:30
We will present results regarding the instability of extremal black holes. We will show how these results can be used to derive observational signatures for extremal black holes.
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David Hilditch (CENTRA, Tecnico Lisbon)12/09/2023, 10:30
Working within the space of smooth solutions of GR and tuning to the threshold of black hole formation, we arrive at extreme spacetimes which are generally expected to contain naked singularities. In the spherical setting such configurations have been accurately studied by numerical work for three decades. This resulted in a beautiful understanding of the threshold of collapse through a...
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Panagiotis Giannadakis (King's College London)12/09/2023, 12:00
We investigate the robustness of inflation models to inhomogeneous initial conditions. In the simplest case inflation is described by a single scalar field $\phi$ minimally coupled to gravity with homogeneous initial value $\phi_0 and canonical momentum $\Pi_0 = 0$. However, there is no fundamental reason to reckon that inflation started with such homogeneous initial conditions. In our recent...
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Argyro Sasli (Aristotle University of Thessaloniki)12/09/2023, 12:00
We explore the potential for detecting low-$|T/W|$ rotational instabilities (known also as dynamical shear instabilities) with future gravitational wave observatories. Our study employs numerically generated post-merger waveforms, which reveal the re-excitation of the l=m=2 f-mode. We evaluate the detectability of these signals by injecting them into colored Gaussian noise. The signals are...
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Dimitrios Pesios12/09/2023, 12:20
Gravitational waves in the post-merger phase of binary neutron star mergers may become detectable with planned upgrades of existing gravitational-wave detectors or with the more sensitive next-generation detectors. A template bank of predicted waveforms can facilitate detection and parameter estimation. However, todate, only a relatively small number of waveforms have been constructed through...
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Theodore Anton (Queen Mary University of London)12/09/2023, 12:20
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Giannis Papagiannopoulos12/09/2023, 12:40
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Christian Krueger (University of Tuebingen)12/09/2023, 12:40
We provide accurate universal relations that allow to estimate the moment of inertia $I$ and the ratio of kinetic to gravitational binding energy $T/W$ of uniformly rotating neutron stars from the knowledge of mass, radius, and moment of inertia of some related non-rotating neutron star. Based on these, several other fluid quantities can be estimated as well. Astrophysical neutron stars rotate...
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Pantelis Pnigouras (University of Alicante)12/09/2023, 13:00
During the late stages of a neutron star binary inspiral finite-size effects come into play, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal. As demonstrated in the case of GW170817—the first direct detection of gravitational waves from a neutron star binary—this can lead to constraints on the neutron star equation of state....
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Antoine Petiteau (CEA/IRFU/DPhP)13/09/2023, 09:30
LISA (Laser Interferometer Space Antenna) is the future large mission by the European Space Agency aimed at observing the Universe with gravitational waves. It was approved in 2017 following the success of the technological demonstrator LISAPathfinder and the detection of gravitational waves by ground-based observatories LIGO-Virgo. LISA has nearly completed its detailed definition phase...
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Christos Charmousis (LPT)13/09/2023, 10:30
I will discuss some explicit solutions of higher order scalar tensor theories. We will start by reviewing classical GR solutions and some of their key properties such as integrability of geodesics in Kerr spacetime. We will then construct stealth solutions, i.e. solutions that are still Einstein metrics but with a non trivial scalar field. We will construct solutions which are distinct from...
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Mokhtar Hassaine13/09/2023, 12:00
Recently, an extension of the standard four-dimensional scalar conformal action, yielding a secondorder field equation that remains conformally invariant, was proposed. In spite of this, the corresponding action is not invariant under conformal transformations and this motivates us to define the notion of non-Noetherian conformal scalar field. In this article, we go further by determining the...
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John Antoniadis13/09/2023, 12:30
I will describe recent developments related to the search for low-frequency gravitational waves with pulsar timing arrays
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Nikolaos Dimakis (Center for Theoretical Physics, College of Physical Science and Technology, Sichuan University, China)13/09/2023, 15:00
In this work we explore the motion of massive particles in curved backgrounds. We demonstrate how new symmetries emerge by distorting the conformal vectors of the spacetime metric and how they lead to additional conserved quantities. Beside (pseudo-)Riemannian geometry, we also apply this scheme to certain Finslerian extensions. Finally, we explain how the emergence of these symmetries is...
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Adolfo Cisterna (Charles University, Institute of Theoretical Physics)13/09/2023, 15:30
This paper investigates the integrability properties of Einstein's theory of gravity in the context of accelerating NUT spacetimes by utilizing Ernst's description of stationary and axially symmetric electro-vacuum solutions. We employ Ehlers transformations, Lie point symmetries of the Einstein field equations, to efficiently endorse accelerating metrics with a nontrivial NUT charge. Under...
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Sergi Sirera Lahoz13/09/2023, 15:30
A nonluminal speed of gravitational waves is a smoking gun signal for the presence of new gravitational physics and hence measurements of this speed can place strong constraints on the theoretical landscape of modified gravity. The ringdown phase of binary black hole mergers, characterised by the so-called quasinormal modes, promises a clean and analytic understanding of deviations from...
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Bertha Cuadros-Melgar (University of Sao Paulo)13/09/2023, 15:50
We investigate some aspects of GB-BTZ black holes. Perturbations associated to scalar and massless spinorial fields are studied suggesting the dynamical stability of the geometry. Moreover, the quasinormal modes are found for different parameters, mainly exploring the influence of the coupling constant of the theory. The hydrodynamical modes are also obtained in the small coupling limit....
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Fatemeh Hossein-Nouri13/09/2023, 15:50
The merger of supermassive black holes (BBH) produces mHz gravitational waves (GW), which are potentially detectable by future Laser Interferometer Space Antenna (LISA). Such binary systems are usually embedded in an accretion disk environment at the center of the active galactic nuclei (AGNs). Recent studies suggest the plasma environment imposes measurable imprints on the GW signal for...
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Georgios Loukes-Gerakopoulos (Astronomical Institute, Czech Academy of Sciences)13/09/2023, 16:10
In this talk we discuss the issue whether the center of the mass of a spinning extended test body moving in a black hole background is just a gauge. The discussion is in the framework of the Mathisson-Papapetrou-Dixon equations, for which a spin supplementary condition is used in order to fix the center of the mass. To get the answer we employ novel and in principle analytical methods of...
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Athanasios Bakopoulos (University of Ioannina)13/09/2023, 16:10
In this work we are revisiting the well studied Ellis wormhole solution in a generalized Horndeski theory motivated from the Kaluza-Klein compactification procedure of the more fundamental higher dimensional Lovelock gravity. We show that the Ellis wormhole is analytically supported by a gravitational theory with a non-trivial coupling to the Gauss-Bonnet term and we expand upon this notion by...
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Theodoros Papanikolaou (National Observatory of Athens)13/09/2023, 17:00
Primordial black holes (PBH) can account for a wide variety of cosmic conundra, among which the origin of the primordial magnetic fields threading the intergalactic medium. In this talk, by considering PBHs naturally furnished with a disk due to the vortexlike motion of the primordial plasma around them, we will propose a novel natural ab initio mechanism for the generation a battery induced...
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Angel Rincon13/09/2023, 17:00
We discuss energy conditions and quasinormal modes for scalar perturbations of regular charged black holes within the framework of General Relativity coupled to non-linear electrodynamics. The frequencies are computed numerically adopting the WKB method, while in the eikonal limit an analytic expression for the spectra is obtained. The impact of the electric charge, the angular degree, and the...
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Dimitra Tseneklidou13/09/2023, 17:20
Core-collapse supernovae are among the most promising future gravitational wave (GW) sources. GW emission is mainly due to the excitation of oscillation modes of the proto-neutron star (PNS) and the stalled accretion shock. Those oscillations will allow in future GW observations to perform asteroseismology to infer properties of the PNS. These oscillations can be represented by a system of...
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Jorge Ovalle13/09/2023, 17:20
Although we cannot understand the true nature of singularities in the framework of GR, it is possible to evade them by following a fairly simple strategy: generate regular BHs by filling the spacetime around the central singularity with some physically reasonable source of matter (which could be consequence of some new gravitational sector). This has produced a plethora of new regular BH...
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Theodoros Nakas (National Technical University of Athens)13/09/2023, 17:40
We develop a general algorithm that enables the consistent embedding of any four-dimensional static and spherically symmetric geometry into any five-dimensional single-brane braneworld model, characterized by an injective and nonsingular warp factor. Furthermore, we supplement the algorithm by introducing a method that allows one to, in principle, reconstruct 5D field theories that support the...
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Subhajit Dandapat13/09/2023, 17:40
Close hyperbolic encounters of black holes (BHs) generate certain Burst With Memory (BWM) events in the frequency windows of the operational, planned, and proposed gravitational wave (GW) observatories. We provide details of our HyperbolicTD & GW_hyp packages that should allow both LIGO-Virgo-KAGRA (LVK) and Pulsar Timing Array (PTA) consortia to search for such BWM events in their respective...
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Naoki Seto (Kyoto University)13/09/2023, 18:00
We discuss exploration for isotropic gravitational wave backgrounds around 1 mHz by correlation analysis, targeting both parity odd and even polarization modes. Even though the space interferometer LISA alone cannot probe the two modes due to cancellations, the outlook is being changed drastically by the strong development of other space detectors such as Taiji. In fact, a heliocentric...
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Dionysios Kokkinos (University of the Aegean)13/09/2023, 18:00
There are various ways to deploy symmetries in order to extract exact solutions of Einstein’s Field Equations. The Study of the Canonical forms of Killing Tensor in the frame of General Theory of Relativity proved fruitful in the past providing new solutions or general families of already known spacetimes. Regarding the latter the most general versions of Killing Tensor, its four Canonical...
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Pierros Ntelis (Aix-Marseille University)13/09/2023, 18:20
In this talk, I will introduce a novel formalism for any field theory and apply it to the effective field theories of large-scale structure. The new formalism is based on functors of actions composing those theories. This new formalism predicts the actionic fields. Furthermore, I will discuss a generalised manifold with N-correlators of Nt- objects with or without contaminants. I will discuss...
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Ippocratis Saltas14/09/2023, 09:30
I will review recently proposed probes of gravity and dark matter based on the oscillations of stars. In this regard, I explain how current and future solar/stellar oscillations can place tight constraints on the properties of dark energy and dark matter.
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Alexander Kamenshchik (University of Bologna)14/09/2023, 10:30
We consider some cosmological models where soft future singularities arise and discuss how the crossing of these singularities can change the properties of matter fields. We also compare different approaches to the possibility of the crossing of the singularities of the Big Bang – Big Crunch type. We discuss what happens with the singularities in quantum cosmology and study what happens with...
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Eugeny Babichev14/09/2023, 12:00
I will present solutions of DHOST theories describing a rotating black hole embedded in an expanding universe. The solution is constructed by conformal transformation of a stealth Kerr(-de Sitter) black hole. The conformal factor depends explicitly on the scalar field - but not on its derivative - and defines the new theory. The scalar field of the stealth Kerr(-de Sitter) solution depends on...
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Rodrigo Olea14/09/2023, 12:30
Within a holographic framework, we explore the physical consequences of embedding Einstein gravity with negative cosmological constant in Conformal Gravity in four dimensions. In the bulk, the procedure is equivalent to Holographic Renormalization, as the Einstein-AdS action appears augmented by the correct boundary counterterms. In codimension-2, 4D Conformal Gravity induces a 2D conformal...
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Theodosios Christodoulakis (National and Kapodistrian University of Athens)14/09/2023, 15:00
The relevant time-depended automorphisms are used to reduce the form of
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the line-element. There are, thus revealed, enough first integrals of motion
which enable the presentation of the entire solution space for the 5-dim
Kasner (4 A_1) and/or Type V (A^{1,1}_{4,5}) models. -
Konstantinos Dialektopoulos14/09/2023, 15:30
Nonparametric reconstructions of cosmological parameters from observational data sets are usually associated with Gaussian processes (GP). It is known though, that GPs are plagued with overfitting issues and they introduce some statistical bias through the selection of the kernel. The last few years, with the advent of Machine Learning, artifical neural networks are being used in cosmology for...
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Maria Petronikolou (National Technical University of Athens)14/09/2023, 15:50
We investigate the alleviation of both H0 and σ8 tensions simultaneously within the framework of Tsallis cosmology. Such a modified cosmological scenario is obtained by the application of the gravity-thermodynamics conjecture, but using the non-additive Tsallis entropy, instead of the standard Bekenstein-Hawking one. Hence, one obtains modified Friedmann equations, with extra terms that depend...
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Charalampos Tzerefos (University of Athens)14/09/2023, 16:10
In this talk I am going to present our recent work where we derive for the first time a three-peaked GW signal associated to no-scale Supergravity within the frequency ranges of nHz, Hz and kHz, with the former being in excellent agreement with NANOGrav/PTA GW data. We concentrate on the primordial gravitational wave (GW) spectrum induced due to second-order gravitational interactions by...
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Genly Leon (Universidad Catolica del Norte)14/09/2023, 17:00
Various studies, such as references 2207.00878 [gr-qc], 2304.14465 [gr-qc], and 2304.14465 [gr-qc], have explored the potential of Fractional Cosmology to address the H0 tension. They have analyzed the Equation of State’s value attained from the Supernova H0 and Planck’s value for z<1.5 and have reported a trend of H0 that aligns with these values. However, there is still a discrepancy between...
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Georgios Doulis (FSU Jena)14/09/2023, 17:20
Entropy is a physical shock detector. Entropy is only produced during irreversible processes, like shocks, therefore it can be used to flag and track highly non-smooth features present in the solution space of the problem we are investigating. In this talk, I will demonstrate how entropy can be employed in the design of a flux-limiter for a number of different problems that can be written in...
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Milton Ruiz14/09/2023, 17:40
Binary neutron star mergers can provide new insights about the equation of state (EoS) above supranuclear densities. Therefore many gravitational wave template banks are under construction. However, it has been suggested that a naive numerical treatment of regions where the sound speed has a non-monotonic dependence with the rest-mass density (the so-called non-convex regions), as the ones...
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Emmanuel Saridakis14/09/2023, 18:00
We summarize the famous tensions between various observational
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datasets and theoretical predictions of the Standard Model of Cosmology,
such as the H0 and S8 tensions, that could be a sign that we are
approaching New Physics. Then we provide possible solutions, arising
from modifications /extensions of the standard lore. -
Anna Marinitsi
We construct an analytic frequency-domain model for gravitational waves in the post-merger phase of binary neutron star mergers. The model is based on an analytic continuous Fourier Transform of the time-domain model presented by Soultanis, Bauswein & Stergioulas (2022). We demonstrate perfect agreement with a numerical FFT in a representative case. We are planning to implement the...
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Argyro Sasli (Aristotle University of Thessaloniki)
In recent years, the field of Gravitational Wave Astronomy has flourished. With the advent of more sophisticated ground-based detectors and space-based observatories, it is anticipated that Gravitational Wave events will be detected at a much higher rate in the near future. One of the future data analysis challenges is performing robust statistical inference in the presence of detector noise...
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Nikiforos Galanis, Dr Nikolaos Karnesis
The goal of this work is to investigate whether it is possible or not to separate and identify an isotropic, Gaussian, Stochastic Gravitational Wave Background (SGWB) from the LISA instrument noise, without making any assumptions about the spectral shapes of both. And, if not, to test whether keeping one shape unknown and using prior knowledge about the shape of the other would allow for an...
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IOANNIS TSIOULIS
In parameter estimation calculations of gravitational wave sources, it is useful to know the optimal signal-to-noise ratio of an individual model waveform. We train an artificial neural network on a random sample of one million theoretical waveforms of binary black hole systems with random spins and achieve an accuracy of 97\% in predicting the signal-to-noise ratio. The neural network...
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We examine the rotational motion of three gravitating neutrinos which are rotating on a circular path. We use Newton’s gravitational Law with gravitational masses and Special Relativity to compute relativistic masses ($\gamma m_o$) and inertial or gravitational mass ($\gamma^3m_o$). By utilizing, as in the Bohr model of the H atom, the de Broglie equation $\gamma m_o{\rm{v}}r=\hbar$, we obtain...
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