28 citations · 80 across the 28 of their papers we have counts for
30 papers
Universal Relations Meet Causality: Bounding the Dynamical Love Number of Neutron Stars
Alex Kehagias, Antonio Riotto
The frequency-dependent tidal response of a neutron star is constrained by causality, reality and passivity, which turn a suitably rescaled response into a holomorphic self-map of…
On the Modes at the Schwarzschild Black Hole Horizon
Dimitrios Giataganas, Alex Kehagias, Antonio Riotto
We discuss the origin of the modes appearing at the Schwarzschild black hole horizon and decaying at integer multiples of the surface gravity. We argue that no excitations generate…
The Schwarzschild Black Hole in an External Gravitational Tidal Field: the Quasinormal Spectrum
Dimitrios Giataganas, Alex Kehagias, Antonio Riotto
A black hole need not ring down in isolation, since a nearby companion can subject it to an external gravitational tide. We calculate how a quadrupole tide modifies the Schwarzschi…
Thermal Origin of Black Hole Quasinormal Modes
D. Giataganas, G. F. Giudice, A. Kehagias +2
When a black hole rings after a merger, it emits gravitational waves at characteristic frequencies known as quasinormal modes (QNMs). In the eikonal limit, these modes are governed…
A Bound on the Dynamical Love Number
Alex Kehagias, Antonio Riotto
The tidal deformability of a compact object is encoded in a single function of frequency, the retarded Green's function relating the induced multipole to the applied tide. Causalit…
Radial Mirror Scattering and the QNM Convergence Region
Alex Kehagias, Antonio Riotto
We revisit the convergence region of the quasinormal modes expansion of Schwarzschild retarded Green functions from a radial scattering viewpoint. The tortoise coordinate admits a…
Black Hole Photon Rings Saturate the Quantum Chaos Bound
D. Giataganas, G. F. Giudice, A. Kehagias +2
We study the quantum chaos bound in the photon ring region surrounding black holes. By evaluating the Lyapunov exponent associated with unstable null geodesics in a broad class of…
Standard Model Higgs Peaks: a Note on the Vacuum Instability during Inflation
G. Franciolini, A. Kehagias, A. Riotto
In the Standard Model, the Higgs potential develops an instability at high field values when the quartic self-coupling runs negative. Large quantum fluctuations during cosmic infla…
Nonlinear Gravity and Multipole Turbulence
A. Ianniccari, A. Kehagias, L. Lo Bianco +1
We derive a kinetic Boltzmann equation characterizing the long-term statistical behavior of the turbulent dynamics of nonlinear interacting gravitational wave multipoles in Minkows…
Schwarzschild Black Hole Turbulence: Scalar Probe
Alex Kehagias, Antonio Riotto
We explore how perturbations of a Schwarzschild black hole can redistribute energy among scalar modes and seed turbulent like cascades. We make use of the van der Pol-Krylov-Bogoli…
Non-vanishing non-linear Static Love Number of a Class of Extremal Reissner-Nordstrom Black Holes
L. R. Gounis, A. Kehagias, G. Panagopoulos +1
We compute the tidal Love numbers for a particular axially symmetric configuration of extremal Reissner-Nordstrom geometry. By exactly solving the non-linear Einstein equations, we…
Nonlinearities of Schwarzschild Black Hole Head-on Collisions
Alex Kehagias, Davide Perrone, Antonio Riotto
We derive analytically the amplitude of the quadratic quasi-normal mode generated in the ringdown stage of the gravitational waveform produced by the ultra-relativistic head-on col…
Nonlinearities in Kerr Black Hole Ringdown from the Penrose Limit
D. Perrone, A. Kehagias, A. Riotto
We provide a fully analytical approach to calculate the nonlinearities of the gravitational waves in the ringdown of a Kerr black hole in the eikonal limit. The corresponding quasi…
The AdS Perspective on the Nonlinear Tails in Black Hole Ringdown
Alex Kehagias, Antonio Riotto
Black holes gradually settle into their static configuration by emitting gravitational waves, whose amplitude diminish over time according to a power-law decay at fixed spatial loc…
Nonlinear Tails of Gravitational Waves in Schwarzschild Black Hole Ringdown
Alex Kehagias, Antonio Riotto
Schwarzschild black holes evolve toward their static configuration by emitting gravitational waves, which decay over time following a power law at fixed spatial positions. We deriv…
Non-linear Quasi-Normal Modes of the Schwarzschild Black Hole from the Penrose Limit
Alex Kehagias, Davide Perrone, Antonio Riotto
The Penrose limit connects a plane wave geometry to the photon ring of a black hole, where the quasi-normal modes are located in the eikonal limit. Utilizing this simplification, w…
The Vanishing of the Non-linear Static Love Number of Kerr Black Holes and the Role of Symmetries
L. -R. Gounis, A. Kehagias, A. Riotto
We investigate the tidal response of Kerr black holes in four-dimensional space-times subjected to external gravitational fields. Using the Ernst formalism and Weyl coordinates, we…
Can We Detect Deviations from Einstein's Gravity in Black Hole Ringdowns?
A. Kehagias, A. Riotto
The quasinormal mode spectrum of gravitational waves emitted during the black hole ringdown relaxation phase, following the merger of a black hole binary, is a crucial target of gr…
Nonlinear Effects in Black Hole Ringdown Made Simple: Quasi-Normal Modes as Adiabatic Modes
A. Kehagias, A. Riotto
The nonlinear nature of general relativity manifests prominently throughout the merger of two black holes, from the inspiral phase to the final ringdown. Notably, the quasi-normal…
Black Holes in a Gravitational Field: The Non-linear Static Love Number of Schwarzschild Black Holes Vanishes
Alex Kehagias, Antonio Riotto
We show that the static tidal Love number of Schwarzschild black holes in four dimensions and in the vacuum vanishes at any order in the external tidal force. We also identify the…
Deciphering the Instability of the Black Hole Ringdown Quasinormal Spectrum
A. Ianniccari, A. J. Iovino, A. Kehagias +4
The spectrum of the quasinormal modes of the gravitational waves emitted during the ringdown phase following the merger of two black holes is of primary importance in gravitational…
A Short Note on the Love Number of Extremal Reissner-Nordstrom and Kerr-Newman Black Holes
Alex Kehagias, Davide Perrone, Antonio Riotto
We provide a simple proof of why the Love number vanishes for extremal Reissner-Nordstrom and Kerr-Newman black holes. The argument is based on a conformal inversion isometry of th…
Why the Universal Threshold for Primordial Black Hole Formation is Universal
Alex Kehagias, Davide Perrone, Antonio Riotto
We show why the threshold for primordial black hole formation is universal (independent from the shape of the perturbation) when expressed in terms of the volume averaged compactio…
The Black Hole Formation -- Null Geodesic Correspondence
Andrea Ianniccari, Antonio J. Iovino, Alex Kehagias +2
We provide evidence for a correspondence between the formation of black holes and the stability of circular null geodesics around the collapsing perturbation. We first show that th…