arXiv subjects

Béatrice Bonga

Publications and source records attributed to Béatrice Bonga.

At least 19 recordsLinked to original sources

arXiv2026

Universality in the Transition from Inspiral to Plunge for Extreme-Mass-Ratio-Inspirals: High-Accuracy Analytic Solutions and Catastrophe Theory

We revisit the transition from inspiral to plunge for extreme mass-ratio inspirals on quasi-circular, inclined orbits in Kerr spacetime from the perspective of catastrophe theory. Our goal is to uncover the mathematical structures underlying the universality of the transition dynamics, which remains governed by the same Painlevé I differential equation as for equatorial inspirals despite the additional complexity. We first analyze the solution of the Painlevé I equation selected by the physical boundary conditions of slowly evolving quasi-circular inspiral at early times. We argue that these conditions uniquely select the tritronquée solution of Painlevé I. We then compare existing high-accuracy analytic approximations of the tritronquée solution with direct numerical integrations of the Painlevé I equation, finding comparable accuracy and improved stability under differentiation and integration for the analytic solution. In the second part of this work, we show that the equilibrium structure of the Kerr radial effective potential admits a natural interpretation in terms of catastrophe theory. Equatorial orbits are associated with the fold catastrophe, while inclined orbits are described by the cusp catastrophe. In both cases, the transition to plunge corresponds to slow evolution across fold lines of the catastrophe manifold, providing a geometric explanation for the universal appearance of the Painlevé I equation in the transition dynamics.

gr-qc↗

arXiv2026

Dissection of a merger-ringdown waveform in the small-mass-ratio limit

Work over the past two decades has unveiled the rich phenomenology of black hole binary mergers and subsequent ringdowns, involving a tapestry of quasinormal modes (QNMs), nonlinearities, tails, transients, and secular effects including gravitational memory. Here we develop a framework for analyzing nonlinear merger-ringdown features in the small-mass-ratio limit, where individual effects can be cleanly isolated. Specializing to the case of a quasicircular, nonspinning black hole binary, we find the waveform sharply divides into a pre-merger extended inspiral phase, a merger phase lasting roughly half a cycle, and a post-merger ringdown dominated by QNMs. We show quadratic QNMs dominate over linear overtones in the ringdown phase for comparable-to-intermediate mass ratios, and we highlight nonlinear effects of gravitational-wave memory, including cubic wave-zone phenomena analogous to horizon absorption effects.

gr-qc↗

arXiv2026

Not All Resonances Are Created Equal: Prioritizing Tidal Resonances in EMRIs

Tidal perturbations from nearby compact objects can drive resonant "kicks" in extreme-mass-ratio inspirals (EMRIs), imprinting potentially detectable phase shifts in LISA-band gravitational waveforms. We provide a systematic survey of these tidal resonances across EMRI parameter space in the weak-tide, three-body hierarchy, treating the perturber as stationary on the resonance timescale. For generic Kerr orbits we compute (i) resonance contours in $(p,e,x)$ that locate where each $(n,k,m)$ resonance is encountered, (ii) the associated resonance duration, and (iii) the jump amplitudes in the angular momentum $L_z$ and the Carter constant $Q$ (with $ΔE$ vanishing by time-translation symmetry in the stationary model). Combining jump amplitudes with resonance durations, we construct a practical ranking of the resonances most relevant for waveform modeling, while emphasizing that even modest resonances may still be important through their influence on the phase at which subsequent resonances are entered. All contour and jump data are publicly available.

gr-qc↗

arXiv2026

Black hole spectroscopy: from theory to experiment

The "ringdown" radiation emitted by oscillating black holes has great scientific potential. By carefully predicting the frequencies and amplitudes of black hole quasinormal modes and comparing them with gravitational-wave data from compact binary mergers we can advance our understanding of the two-body problem in general relativity, verify the predictions of the theory in the regime of strong and dynamical gravitational fields, and search for physics beyond the Standard Model or new gravitational degrees of freedom. We summarize the state of the art in our understanding of black hole quasinormal modes in general relativity and modified gravity, their excitation, and the modeling of ringdown waveforms. We also review the status of LIGO-Virgo-KAGRA ringdown observations, data analysis techniques, and the bright prospects of the field in the era of LISA and next-generation ground-based gravitational-wave detectors.

gr-qc↗

arXiv2026

Convergence of post-Newtonian for quasi-circular non-precessing comparable mass ratios BBHs

Post-Newtonian (PN) theory provides the analytic foundation for modeling the early inspiral of binary black holes. However, as an asymptotic series, successive PN orders do not necessarily improve agreement with the full nonlinear dynamics. While this has been explored in the extreme-mass-ratio limit, comparable-mass systems most relevant to current observations have not been benchmarked as systematically at high PN order. We study the convergence of the PN series for non-spinning and quasi-circular systems by comparing the PN energy flux at future null infinity to a long, high-accuracy numerical relativity (NR) simulation. To enable a gauge-consistent comparison, we place both descriptions in the same BMS frame and calibrate the intrinsic PN parameters by fitting to the NR waveform in the early inspiral. We find that for orbital velocities $v\lesssim0.45$, higher PN orders continue to reduce the PN--NR flux discrepancy, with (incomplete) 6PN providing the best agreement among the orders considered. The improvement with PN order is non-monotonic with local extrema around 2.5PN and 4PN. This implies that the optimal truncation order of the PN series cannot be identified from the first local minimum in the energy flux residuals, contrary to suggestions in earlier work. As $v$ approaches $\sim 0.5$ near the innermost circular orbit, higher PN orders no longer improve the agreement between NR and PN, indicating a loss of convergence. These results motivate continued high-order PN calculations and clarify the NR accuracy needed to validate them.

gr-qc↗

arXiv2026

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

gr-qc↗

arXiv2026

Entanglement and correlations between local observables in de Sitter spacetime

Studies of quantum field entanglement in de Sitter space based on the von Neumann entropy of local patches have concluded that curvature enhances entanglement between regions and their complements. Similar conclusions about entanglement enhancement have been reached in analyses of Fourier modes in the cosmological patch of de Sitter space. We challenge this interpretation by adopting a fully local approach: examining entanglement between pairs of field modes compactly supported within de Sitter's cosmological patch. Our approach is formulated in terms of the properties of a metric tensor and an associated complex structure induced by the Bunch-Davies vacuum on the classical phase space. We find that increasing curvature increases correlations between local modes but, somewhat counterintuitively, decreases their entanglement. Our methods allow us to characterize how entanglement is spatially distributed, revealing that a cosmological constant, even if tiny, qualitatively alters the vacuum's entanglement structure. We show that our results are compatible with previous entropy-based studies when properly interpreted. Our findings have implications for entanglement between observables generated during cosmic inflation.

gr-qc↗

arXiv2026

ESO Expanding Horizon White Paper: Revealing the properties of matter at supranuclear densities with gravitational waves

Understanding dense matter under extreme conditions is one of the most fundamental puzzles in modern physics. Complex interactions give rise to emergent, collective phenomena. While nuclear experiments and Earth - based colliders provide valuable insights, much of the quantum chromodynamics phase diagram at high density and low temperature remains accessible only through astrophysical observations of neutron stars, neutron star mergers, and stellar collapse. Astronomical observations thus offer a direct window to the physics on subatomic scales with gravitational waves presenting an especially clean channel. Next-generation gravitational - wave observatories, such as the Einstein Telescope, would serve as unparalleled instruments to transform our understanding of neutron star matter. They will enable the detection of up to tens of thousands of binary neutron star and neutron star - black hole mergers per year, a dramatic increase over the few events accessible with current detectors. They will provide an unprecedented precision in probing cold, dense matter during the binary inspiral, exceeding by at least an order of magnitude what current facilities can achieve. Moreover, these observatories will allow us to explore uncharted regimes of dense matter at finite temperatures produced in a subset of neutron star mergers, areas that remain entirely inaccessible to current instruments. Together with multimessenger observations, these measurements will significantly deepen our knowledge of dense nuclear matter.

astro-ph.IM↗

arXiv2025

Quadratic quasi-normal mode dependence on linear mode parity

Quasinormal modes (QNMs) uniquely describe the dominant piece of the gravitational-wave ringdown of postmerger black holes. While the linear QNM regime has been extensively studied, recent work has highlighted the importance of second-perturbative-order, quadratic QNMs (QQNMs) arising from the nonlinear coupling of linear QNMs. Previous attempts to quantify the magnitude of these QQNMs have shown discrepant results. Using a new hyperboloidal framework, we resolve the discrepancy by showing that the QQNM/QNM ratio is a function not only of the black hole parameters but also of the ratio between even- and odd-parity linear QNMs: the ratio QQNM/QNM depends on what created the ringing black hole, but only through this ratio of even- to odd-parity linear perturbations.

gr-qc↗

arXiv2024

Wave optics for rotating stars

Gravitational lensing in wave optics is a rich field combining caustic singularities, general relativity and interference phenomena. We present a detailed evaluation of wave optics effects resulting from the frame-dragging of a rotating star modeled by a Lense-Thirring spacetime. We demonstrate that, contrary to what was previously stated in the literature, the spin of the star leaves an intricate imprint on the interference fringes and the caustics of the lensed source. This interference pattern can in principle be used to directly measure the spin of the lens.

gr-qc↗

arXiv2024

Inflation does not create entanglement in local observables

Using modern tools of relativistic quantum information, we compare entanglement of a free, massive scalar field in the Bunch-Davies vacuum in the cosmological patch of de Sitter spacetime with that in Minkowski spacetime. There is less entanglement between spatially localized field modes in de Sitter, despite the fact that there is more entanglement stored in the field on large scales. This shows that inflation does not produce entanglement between local observables.

gr-qc↗

arXiv2024

The multimode nature of spacetime entanglement in QFT

We demonstrate the presence of multimode entanglement in the vacuum state of a free, massless scalar quantum field in four-dimensional flat spacetime between two sets of field modes, each contained within a spacetime region that is causally disconnected from the other. This is true despite the fact that entanglement between pairs of individual field modes is sparse and appears only when the two individual modes are carefully selected. Our results reveal that, while entanglement between individual modes is limited, bipartite multimode entanglement in quantum field theory is ubiquitous. We further argue that such multimode entanglement is operationally extractable, and it forms the basis of the entanglement commonly discussed in entanglement harvesting protocols.

quant-ph↗

arXiv2024

Probing Spin-Induced Quadrupole Moments in Precessing Compact Binaries

Spin-induced quadrupole moments provide an important characterization of compact objects, such as black holes, neutron stars and black hole mimickers inspired by additional fields and/or modified theories of gravity. Black holes in general relativity have a specific spin-induced quadrupole moment, with other objects potentially having differing values. Different values of this quadrupole moment lead to modifications of the spin precession dynamics, and consequently modifications to the inspiral waveform. Based on the spin-dynamics and the associated precessing waveform developed in our previous work, we assess the prospects of measuring spin-induced moments in various black hole, neutron star, and black-hole mimicker binaries. We focus on binaries in which at least one of the objects is in the mass gap (similar to the $2.6 M_\odot$ object found in GW190814). We find that for generic precessing binaries, the effect of the spin-induced quadrupole moments on the precession is sensitive to the nature of the mass-gap object, i.e., whether it is a light black hole or a massive neutron star. So that this is a good probe of the nature of these objects. For precessing black-hole mimicker binaries, this waveform also provides significantly tighter constraints on their spin-induced quadrupole moments than the previous results obtained without incorporating the precession effects of spin-induced quadrupole moments. We apply the waveform to sample events in GWTC catalogs to obtain better constraints on the spin-induced quadrupole moments, and discuss the measurement prospects for events in the O$4$ run of the LIGO-Virgo-KAGRA Collaboration.

gr-qc↗

arXiv2024

Nonlinear ringdown at the black hole horizon

The gravitational waves emitted by a perturbed black hole ringing down are well described by damped sinusoids, whose frequencies are those of quasinormal modes. Typically, first-order black hole perturbation theory is used to calculate these frequencies. Recently, it was shown that second-order effects are necessary in binary black hole merger simulations to model the gravitational-wave signal observed by a distant observer. Here, we show that the horizon of a newly formed black hole after the head-on collision of two black holes also shows evidence of non-linear modes. Specifically, we identify one quadratic mode for the $l=2$ shear data, and two quadratic ones for the $l=4,6$ data in simulations with varying mass ratio and boost parameter. The quadratic mode amplitudes display a quadratic relationship with the amplitudes of the linear modes that generate them.

gr-qc↗

arXiv2023

How ubiquitous is entanglement in quantum field theory?

It is well known that entanglement is widespread in quantum field theory, in the following sense: every Reeh-Schlieder state contains entanglement between any two spatially separated regions. This applies, in particular, to the vacuum of a non-interacting scalar theory in Minkowski spacetime. Discussions on entanglement in field theory have focused mainly on subsystems containing infinitely many degrees of freedom -- typically, the field modes that are supported within a compact region of space. In this article, we study entanglement in subsystems made of finitely many field degrees of freedom, in a free scalar theory in $D+1$-dimensional Minkowski spacetime. The focus on finitely many modes of the field is motivated by the finite capabilities of real experiments. We find that entanglement between finite-dimensional subsystems is {\em not common at all}, and that one needs to carefully select the support of modes for entanglement to show up. We also find that entanglement is increasingly sparser in higher dimensions. We conclude that entanglement in Minkowski spacetime is significantly less ubiquitous than normally thought.

quant-ph↗

arXiv2023

Gravitational radiation with $Λ>0$

We study gravitational radiation for a positive value of the cosmological constant $Λ$. We rely on two battle-tested procedures: (i) We start from the same null coordinate system used by Bondi and Sachs for $Λ= 0$, but, introduce boundary conditions adapted to allow radiation when $Λ>0$. (ii) We determine the asymptotic symmetries by studying, à la Regge-Teitelboim, the surface integrals generated in the action by these boundary conditions. A crucial difference with the $Λ=0$ case is that the wave field does not vanish at large distances, but is of the same order as de Sitter space. This novel property causes no difficulty; on the contrary, it makes quantities finite at every step, without any regularization. A direct consequence is that the asymptotic symmetry algebra consists only of time translations and space rotations. Thus, it is not only finite-dimensional, but smaller than de Sitter algebra. We exhibit formulas for the energy and angular momentum and their fluxes. In the limit of $Λ$ tending to zero, these formulas go over continuously into those of Bondi, but the symmetry jumps to that of Bondi, Metzner and Sachs. The expressions are applied to exact solutions, with and without radiation present, and also to the linearized theory.

gr-qc↗

arXiv2023

Resonant dynamics of extreme mass-ratio inspirals in a perturbed Kerr spacetime

Extreme mass-ratio inspirals (EMRI) are one of the most sensitive probes of black hole spacetimes with gravitational wave measurements. In this work, we systematically analyze the dynamics of an EMRI system near orbital resonances, assuming the background spacetime is weakly perturbed from Kerr. Using the action-angle formalism, we have derived an effective resonant Hamiltonian that describes the dynamics of the resonant degree of freedom, for the case that the EMRI motion across the resonance regime. This effective resonant Hamiltonian can also be used to derive the condition that the trajectory enters/exits a resonant island and the permanent change of action variables across the resonance with the gravitational wave radiation turned on. The orbital chaos, on the other hand, generally leads to transitions between different branches of rotational orbits with finite changes of the action variables. These findings are demonstrated with numerical orbital evolutions that are mapped into representations using action-angle variables. This study is one part of the program of understanding EMRI dynamics in a generic perturbed Kerr spacetime, which paves the way of using EMRIs to precisely measure the black hole spacetime.

gr-qc↗

arXiv2022

Efficient fully precessing gravitational waveforms for binaries with neutron stars

We construct an efficient frequency domain waveform for generic circular compact object binaries that include neutron stars. The orbital precession is solved on the radiation reaction timescale (and then transformed to the frequency domain), which is used to map the non-precessional waveform from the source frame of the binary to the lab frame. The treatment of orbital precession is different from that for precessional binary black holes, as $χ_{\rm eff}$ is no longer conserved due to the spin-induced quadrupole moments of neutron stars. We show that the new waveform achieves $\le 10^{-4}$ mismatch compared with waveforms generated by numerically evolved precession for neutron star-black hole systems for $\ge 90\%$ configurations with component mass/spin magnitude assumed in the analysis and randomized initial spin directions. We expect this waveform to be useful to test the nature of the mass-gap objects similar to the one discovered in GW 190814 by measuring their spin-induced quadrupole moments, as it is possible that these mass-gap objects are rapidly spinning. It is also applicable for the tests of black hole mimickers in precessional binary black hole events, if the black hole mimicker candidates have nontrivial spin-induced quadrupole moments.

gr-qc↗