Over the past ten years, the LIGO and Virgo observatories—and now KAGRA—have transformed gravitational-wave detection from an audacious dream into a powerful and routine window onto the cosmos. This talk will retrace that remarkable journey, beginning with the historic first detection of GW150914 on September 14, 2015—a breakthrough that inaugurated gravitational-wave astronomy and forever...
The spins of black holes in binaries observed with gravitational waves are an essential probe of physics on multiple scales, from the astrophysical formation environments of compact binaries to fundamental physics. At the same time, the imprint of spin on the observed signals is weak, making constraints more challenging compared to the other key property of black holes, namely their mass. I...
I will discuss the interplay between the behaviour of particle physics and gravity as we observe them in our “every day”-experiments and observations, and the embedding of these effective description within a meaningful quantum theory of gravity, emphasizing the subtle relation to causality.
The classical Penrose inequality (PI), a relation between the ADM mass and the area of any cross section of the black hole event horizon, was introduced as a test of the weak cosmic censorship: if it fails, the trapped surface is not necessarily behind the event horizon and a naked singularity could form. Since that original derivation, a variety of proofs have developed, mainly focused on the...
We will discuss the framework of quadratic gravity where both General Relativity (GR) and "hairy" black holes coexist. We explore the phenomenology of the solutions and go over the regime of stability. We will then examine quadratic gravity as a candidate for beyong-GR effects in current and upcoming gravitational wave (GW) observations.
There exists a duality in the form of a non-local field redefinition that maps two different Galileon theories into each other while preserving scattering amplitudes. This duality arises naturally in the context of massive gravity and bigravity theories where the Galileon emerges in the decoupling limit as the helicity zero mode of the massive graviton, with the duality being the decoupling...
In the present talk I will describe the first analytic example of a gravitating Skyrmion of unit Baryonic charge in General Relativity minimally coupled to Skyrme model in (3+1) dimensions. I will describe the remarkable properties of this analytic solution and how such gravitating soliton gave rise to the first analytic solutions with non-vanishing Baryonic charge of the Skyrme model on flat...
I will discuss how to construct an EFT that captures non-conservative effects based on recent developments in Schwinger-Keldysh (SK) EFTs. The leading dissipative terms added to the SK action deform the conservation laws in a controlled manner, as demonstrated by two representative examples: Maxwell's theory and general relativity. I will also briefly discuss phenomenological applications in inflation.
I will show how the Belinfante-Rosenfeld improvement terms, that render the energy-momentum tensor symmetric, emerge by coupling the matter to the affine-connection. In this sense the improvement terms correspond to the hypermomentum (microproperties) of matter. I will show how this is realized in two standard examples, the Maxwell field and the Dirac field. I will also show how the...
Assuming that gravity on cosmological scales is described by General Relativity (GR), observations indicate that 80% of matter is in the form dark matter. The underlying cosmological model, ΛCDM, provides a superb fit to the data on scales of around 1 Mpc or larger. However, the dark matter particle responsible is so far undetected. Moreover, galactic dynamics display an element of regularity,...
In the new era of gravitational wave (GW) astronomy, we have access to a new window to investigate cosmology. In this talk, I am going to focus on the so-called scalar induced (stochastic) gravitational waves (SIGW) and how they can act as probes of the early Universe as well as the underlying gravitational theory itself. Specifically, the main results of my PhD thesis will be presented, which...
In this talk, I will present a machine learning approach to reconstructing cosmological dynamics using artificial neural networks (ANNs), applied to late-time expansion, structure growth, and scalar-tensor gravity models. This non-parametric method learns directly from observational data—such as cosmic chronometers, BAO, and supernovae—while incorporating realistic uncertainties and...
I will present some theoretical and observational cosmological constraints on classes of alternative gravitational theories.
In the presence of an active source like primordial magnetic fields (PMFs), the vector perturbations of the metric do not necessarily decay away, but may become significant depending upon the background equation-of-state (EoS) parameter, $w$ for instance during reheating. In this work, we develop a generic formalism for the study of tensor perturbations induced at second order by first-order...
We introduce a novel type of (integrable) vectorial nonmetricity, extending the previous literature by the inclusion of a cubic, completely symmetric term, reminiscent of statistical manifolds. The vectorial degree of freedom and three coefficients completely determine the geometric properties of the proposed connection. We find conditions on these coefficients, which guarantee the...
We study a class of symmetry operators acting on vector perturbations in the Kerr spacetime and employ them to generate new solutions of Maxwell equations. The operators are second-order in derivatives and are directly constructed from the principal Killing-Yano tensor. One of them reproduces a known result from the Debye potential theory, while the other yields a novel symmetry. When applied...
We investigate the effects of large scalar inhomogeneities during the kination epoch, a period in which the universe’s dynamics are dominated by the kinetic energy of a scalar field, by fully evolving Einstein’s equations using numerical relativity. By tracking the non-linear growth of scalar perturbations with both sub-horizon and super-horizon initial wavelengths, we are able to compare...
In this work we present a new solution of a black hole surrounded by massive vector fields in the context of Kaluza-Klein theory. This vector field corresponds to a spin-1 graviton that modifies the law of gravity and allows the effects attributed to dark matter in the universe. In order to analyze the influence of the parameters associated to this solution, we perturb the geometry with a...
When a black hole (BH) rings due to some external perturbation, it emits gravitational waves described by quasi-normal modes (QNMs) – a series of exponentially damped harmonic oscillations. If the Kerr(-Newman) metric fully describes the BH, QNMs carry a unique signature of the BH parameters encoded in the modes' complex frequencies. Consequently, any deviation in the QNMs spectrum from the...
We present a comprehensive dynamical analysis of scalar-field Quintom cosmological models,focusing on scenarios with exponential potentials and both quintessence and phantom compo nents. These models accommodate transitions across the phantom divide (w = −1), permittingrich cosmological behavior including multiple inflationary epochs and bouncing solutions. Em ploying a compact phase-space...
Dark matter remains one of the major open problems in modern cosmology, and PBHs provide a natural and compelling candidate, with the potential to constitute a significant fraction of it. Simultaneously, General Relativity may require modification, particularly in the early universe. In this work, we explore a novel inflationary scenario within Horndeski gravity, focusing on a subclass with a...
Gravitational Waves (GW) emission is usually studied within the framework of the Regge-Wheeler-Zerilli equations, which are not exact and often times require numerical integration or extrapolation (a process which involves tuning additional parameters). Our aim is to prescribe a theoretical framework which alleviates some of these technical challenges by employing a Lehmann-Symanzik-Zimmerman...
We present a model of black hole scalarization where a scalar field couples simultaneously to the Gauss–Bonnet invariant and a U(1) gauge field (can be identified as a dark photon or an electromagnetic field). This combined interaction broadens the conditions for spontaneous scalarization and unify the previous models in one. framework. We track how the electric charge and the two coupling...
The question "How do we use quantum gravity to understand modern cosmology?" is on the same footing as "How do we use quantum gravity to understand the Standard Model?" The Swampland conjectures distill our lessons about quantum gravity from string theory, the holographic principle, and black-hole physics, imposing powerful constraints on and continually deepen our understanding of low-energy...
We present our work on a class of brane-world models that consist of a flat 3-brane embedded in a five-dimensional bulk space filled with a fluid that satisfies a non-linear equation of state of the form $p=\gamma\rho^{\lambda}$, where $p$ is the ‘pressure’ and $\rho$ is the ‘density’ depending on the fifth space coordinate, and $\gamma$, $\lambda$ are parameters. We show that for $\gamma<0$...
We derive the explicit form of the Einstein-Gauss-Bonnet field equations for D-dimensional geometries that admit non-twisting, shear-free, and expanding null geodesic congruences, forming thus the famous Robinson-Trautman class of spacetimes, and discuss their structure and particular solutions. In D=4 GR, this class contains Weyl type II spacetimes or algebraically more special solutions such...
We explore the potential of f(Q) gravity as an alternative framework to address the $H_0$ and $S_8$ tensions in cosmology. Focusing on three representative f(Q) models, we perform a comprehensive Bayesian analysis using a combination of cosmological observations, including cosmic chronometers, Type Ia supernovae, gamma-ray bursts, baryon acoustic oscillations, and redshift-space...
We construct explicit rotating solutions in Einstein's theory of relativity with a minimally coupled free scalar field rederiving and finding solutions in four or five spacetime dimensions. These spacetimes describe, in particular, the back-reaction of a free scalar field evolving in a Kerr spacetime. Adapting the general integrability result obtained many years ago from Eriş-Gürses to simpler...
We present an algorithm to obtain exact black holes endowed with primary scalar hair within the shift-symmetric and $Z_2$-symmetric subclass of beyond Horndeski theories. These solutions depend, in addition to the conventional mass parameter, on a second free parameter encoding primary scalar hair. In the limit of vanishing scalar hair, the solutions smoothly reduce to the Schwarzschild,...
We review the solution space for the field equations of Einstein's General Relativity for various static, spherically symmetric spacetimes. We consider the vacuum case, represented by the Schwarzschild black hole; the de Sitter-Schwarzschild geometry, which includes a cosmological constant; the Reissner-Nordström geometry, which accounts for the presence of charge. Additionally we consider the...
Einstein's equations imply that a gravitationally collapsed object forms an event horizon. But what lies on the other side of this horizon? In this talk, I am going to discuss the results of our new paper (https://arxiv.org/abs/2412.09558 ), presenting an alternative, topologically distinct solution: the Black Mirror. In the black hole solution, the horizon connects the exterior metric to an...
I will review recent work to apply self-force methods to the black-hole scattering problem in the extreme-mass-ratio domain, enabling useful comparisons with similar calculations in post-Minkowskian theory. In particular, I will demonstrate how benchmarking of scattering observables using self-force data can inform efficient resummations of post-Minkowskian formulas that remain accurate even...
Machine Learning is finding diverse applications in the field of astrophysics and gravitational wave astronomy. This talk surveys our recent advancements in applying such methodologies. We demonstrate the utility of Deep Residual Networks (ResNets) in discovering new gravitational wave events from binary black hole mergers. Next, we present the calculation of the astrophysical detection...
The detection of gravitational waves has revolutionized our understanding of the universe, offering unprecedented insights into its dynamics. A major goal of gravitational wave data analysis is to speed up the detection and parameter estimation process using machine learning techniques, in light of an anticipated surge in detected events that would render traditional methods impractical. Here,...
Extreme-mass-ratio inspirals (EMRIs) are binary systems composed of a primary supermassive black hole and a secondary compact object of stellar mass. Owing to their significant mass disparity, EMRIs emit gravitational waves in the millihertz frequency band, making them accessible only to future space-based detectors such as LISA. These systems evolve adiabatically, with the secondary...
Conventional searches for gravitational wave signals in detector data are computationally demanding and struggle when certain transient noise sources are present. Recently, machine-learning algorithms have been proposed to address current and future challenges. We present a neural-network based algorithm to search for binary black hole waveforms. We also apply our algorithm to real O3b data...
We used AresGW, a deep residual neural network for gravitational wave detection, to process O3 data from the two LIGO detectors, generating a list of triggers with high significance. To improve the false alarm rate, we also used Gravity Spy, a convolutional neural network designed to identify glitches. We processed ARESGW triggers by removing those that were common between the two networks....
The recent detections from the EHT Collaboration of the shadows generated by the supermassive objects at the heart of M87 and Milky Way galaxies has prompted a new era in theoretical strong-field astrophysics. In this talk I will discuss the theoretical and basis of this new observational window and its latent power for distinguishing between canonical black holes, regular black holes, and...
The future space-borne gravitational wave observatory LISA may provide the first single event measurement of permanent marks in the fabric of spacetime that remember the passage of a gravitational wave. This effect, known as gravitational memory, is one of the most intriguing predictions of general relativity that has not been observed yet. After offering a particularly illuminating...
Extended gravitational models have gained large attention in the last couple of decades. In this talk, I'll examine the solution space of vacuum, static, and spherically symmetric spacetimes within F(R) theories, introducing novel methods that reduce the vacuum equations to a single second-order equation. I'll derive analytic expressions for the metric functions in terms of the arbitrary...
The gravitational waves (GWs) that we have detected so far are emitted by compact binaries where the mass ratio between the two objects is of order 1:1 to 1:10. Third-generation GW detectors will instead allow us to receive different signals, like the ones coming from black hole binaries with a larger mass ratio, from 1:100 up to 1:10^6. The orbits of such systems are expected to be eccentric...
Almost four decades have passed since the generalization of vacuum Kerr solutions to higher dimensions in the form of Myers–Perry black holes, yet an exact solution generalizing their charged extension (Kerr-Newman) to higher dimensions remains unknown in Einstein-Maxwell theory. In this talk, I will discuss this issue from the viewpoint of the (generalized) Kerr–Schild class. Time permitting,...
This talk concerns the computation of the stochastic gravitational wave (GW) background generated by black hole-black hole (BH-BH) hyperbolic encounters with eccentricities close to one and their comparison with the respective sensitivity curves of planned GW detectors. In this study we took into account hyperbolic encounters that take place in clusters up to redshift 5 and with BH masses...
I will discuss properties of general stationary and axisymmetric spacetimes, with a particular focus on circularity - an accidental symmetry enjoyed by the Kerr metric, and therefore widely assumed when searching for rotating black hole solutions in alternative theories of gravity as well as when constructing models of Kerr mimickers. It can be shown the local existence of a Kerr-like gauge,...
There has been a surge of interest into collisional Penrose process after Bañados, Silk and West described an idealised edge case, in which particles coming from rest at infinity can collide with arbitrarily high centre-of-mass collision energy close to the horizon of a black hole. However, it turned out that in the vacuum case, there is an unconditional upper bound on the efficiency of...
The tidal response of compact objects reflects the underlying gravitational theory and leaves imprints on the gravitational waveforms emitted during the inspiral phase of binary coalescences. High-precision modeling that includes higher-order post-Newtonian effects is essential to test gravity in a strong regime through constraints on such tidal responses. In this talk, I present a formulation...
In this work we compute novel analytical expressions for differential curvature invariants for accelerating Kerr-Newman black holes in (anti-)de Sitter spacetime. We explore and prove that some of the calculated frame agnostic scalar polynomial invariants (SPIs), can be used on the detection of horizon and ergosurfaces of this important class of black holes. Using the Bianchi identities we...
Nuclear star clusters (NSCs), found in most galaxies, appear as compact stellar systems located around supermassive black holes (SMBHs) in their centers. They often contain a mix of old and young stars and frequently exhibit signs of recurrent star formation. SMBHs define the loss cone of small angular momentum orbits that plunge to the immediate vicinity of the event horizon, where tidal...
Binary neutron star mergers (BNSM) are associated with powerful gravitational and electromagnetic astronomical transients. Multimessenger observations of BNSMs promise to deliver unprecedented insights on fundamental physics questions, including constraints on dense matter models and the production of heavy elements. Detailed theoretical predictions of the merger dynamics are crucial for...
Testing the relativistic strong-field dynamics of general relativity (GR) has been a major motivation in the century-long quest to detect gravitational waves (GWs). Since the first GW detection in 2015, we have been probing the dynamics of gravity and the nature of compact objects, by analysing the observed signals from coalescing black holes and neutron stars. In this talk, I will review the...
It has been shown that spherical orbits around Kerr black holes remain
spherical (zero eccentricity) under the influence of gravitational
radiation reaction in the adiabatic limit. I will show that spherical
orbits in non-Kerr black holes that still preserve most of the good
qualities and symmetries of Kerr spacetime can access certain resonances
in such a way that an initially spherical...
Our latest study (2407.18845) investigates the possibility of generating gravitational waves (GWs) from a curvature-induced phase transition of a non-minimally coupled scalar dark matter field with a Higgs-portal. This analysis is conducted during the transition from inflation to kination for various inflationary scales, considering both positive and negative values of the non-minimal...
In this work, we perform a Bayesian analysis putting together the available knowledge from the nuclear physics experiments and astrophysical observations to explore the equation of state of supranuclear matter. In particular, we employ a relativistic metamodeling technique to nuclear matter to cover the uncertainties in the parameter space of the saturation properties of nuclear matter, both...
Neutron stars provide an ideal theoretical framework for exploring fundamental physics when nuclear matter surpasses densities encountered within atomic nuclei. Despite their paramount importance, uncertainties in the equation of state (EoS) have shrouded their internal structure. For rotating neutron stars, the shape of their surface is contingent upon the EoS and the rotational dynamics....
Motivated by the complex phenomena occurring in the vicinity of accreting black holes, this study revisits how additional matter distorts otherwise integrable geodesic motion. Whereas most earlier work considered static, axis-symmetric configurations, real accretion discs rotate and drag the surrounding space-time. To quantify the dynamical impact of this rotation-induced frame-dragging,...
This talk explores the overlooked spin-1/2 sector of basic supergravity, challenging the long-standing view—present since the origins of supergravity in the late 1970s—that it is non-physical. We show that this belief arose from assuming the validity of the Dirac conjecture of the theory of constrained Hamiltonian systems. We demonstrate that the conjecture does not hold in this particular...
Algebraically general solutions in General Relativity are notably rare and less mathematically tractable compared to their algebraically special counterparts. Nevertheless, this kind of solutions is quite interesting in mathematical and physical point of view.
In a previous study conducted in vacuum with cosmological constant under the framework of Newman-Penrose formalism, we explored an...
The worldline of an extended body in curved spacetime can be described by the Mathisson-Papapetrou-Dixon equations when its centroid, i.e., its center of mass, is fixed by a spin supplementary condition (SSC). Different SSC choices result in distinct worldlines. To examine the properties of these choices, we investigate the frequency of circular equatorial orbits of extended bodies within the...
I will discuss the Cauchy problem of self-interacting massive vector fields, and explain why they often face instabilities and apparent pathologies. After showing that these issues are due to the breakdown of the well-posedness of the corresponding initial-value problem, I will characterize the well-posedness breakdowns and explicity show that they can be avoided by fixing the equations in a...
I will clarify that higher-derivative theories and associated opposite-sign kinetic terms are no obstruction for long-lived classical motion. For point-particle models, integrability allows for proof of global stability. For scalar field theories, mathematical theorems establish well-posed time evolution for sufficiently small, compactly-supported initial data and numerical scattering...
We explore symmetric and discontinuous integrators for solving partial differential equations (PDEs) over long periods. Explicit solvers are Courant-limited and fail to preserve Noether symmetries, impacting their effectiveness in long-time integration scenarios. We thus explore symmetric (exponential, Padé, or Hermite) integrators, which are unconditionally stable and known to preserve...
Merging massive black hole binaries (MBHBs) are important gravitational wave (GW) sources for the future space-based observatory LISA. The GW signal from the merger will be detected throughout the entire Universe. Characterization of the GW signal allows us to infer masses and spins of MBHs, the position of the source in the sky and the distance. This information will allow us to understand...
We study the dynamics of the interacting models between the Gauss-Bonnet (GB) coupled scalar field and the dark matter fluid in a homogeneous and isotropic background. A key feature of GB coupling models is the varying speed of gravitational waves (GWs). We utilize recent constraints on the GW speed and conduct our analysis in two primary scenarios: model-dependent and model-independent. In...
We derive the equations of motion of a test particle with intrinsic hypermomentum in spacetimes with both torsion S and nonmetricity Q (along with curvature R). Accordingly, S and Q can be measured by tracing out the trajectory followed by a hypermomentum-charged test particle in such a non-Riemannian background. The test particle is approximated by means of a Dirac δ-function. Thus we find a...
The detection of gravitational waves (GWs) from compact binary mergers has transformed astrophysics and pushed the development of more efficient search methods. While matched-filtering remains the standard, the growing data volumes from LIGO, Virgo, and KAGRA have spurred interest in machine learning (ML) for its scalability. This work evaluates the sensitivity of AresGW model 1, an ML-based...
