arXiv subjects

Alessandra Buonanno

Publications and source records attributed to Alessandra Buonanno.

At least 37 records · Page 2Linked to original sources

arXiv2026

Advancing the Effective-One-Body Framework in the Test-Mass Limit

We present SEOB-TML, an enhanced effective-one-body (EOB) framework for the test-mass limit, optimized for quasi-circular, spin-aligned binary black holes. On the dynamical side, we introduce a quadrupole-factorized (Q-factorized) prescription that maps the total energy flux-including horizon absorption-onto a single (2,2) mode baseline. This approach effectively captures higher-order multipole contributions without explicit mode summation, while simultaneously leading to a dramatic reduction in fractional flux errors. To ensure a smooth transition to the post-merger stage, we replace traditional next-to-quasicircular corrections with a phenomenological ansatz, enabling a flexible, mode-dependent attachment prescription. For the merger-ringdown stage, we utilize quasi-normal mode coefficients extracted from numerical waveforms via qnmfinder to explicitly model mode-mixing effects. These enhancements lead to a substantial reduction in residuals, capturing the complex physical modulations prominent in retrograde configurations. Additionally, we implement the (2,0) mode across the full waveform, further extending the model's physical coverage and accuracy. Overall, our framework generates highly accurate late inspiral-merger-ringdown waveforms for extreme-mass-ratio systems, significantly reducing dephasing and improving the near-merger reconstruction. We demonstrate the performance of SEOB-TML against the current state-of-the-art SEOBNRv5HM model, highlighting how our specialized developments extend the reliability of the EOB framework into the test-mass limit.

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arXiv2026

deci-Hz Gravitational Wave Observations on the Moon and Beyond

This document summarizes talks and discussions from the workshop "deci-Hz Gravitational Wave Observations on the Moon and Beyond" that took place at Johns Hopkins University between September 1 and September 3, 2025. The workshop focused on experimental proposals to observe gravitational waves in the deci-Hz band, including lunar detectors, laser interferometers in space, and atom interferometry; gravitational wave sources in the deci-Hz frequency band; and the multi-messenger and multi-band astronomy that would be enabled by these observations.

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arXiv2026

Plunge-Merger-Ringdown Tests of General Relativity with GW250114

The binary black hole signal GW250114, the clearest gravitational wave detected to date, offers a unique opportunity to test general relativity in the relativistic strong-gravity regime. How well does GW250114 agree with Einstein's predictions in the plunge-merger-ringdown stage? To address this point, we constrain deviations from general relativity across the plunge-merger-ringdown stage of spin-precessing binaries with a parametrized waveform model within the effective-one-body formalism. We find that deviations from the peak gravitational-wave amplitude and instantaneous frequency of the $(\ell, |m|)=(2,2)$ mode are constrained to about $10\%$ and $4\%$, respectively, at $90\%$ credible level. These constraints are, respectively, two and four times more stringent than those obtained by analyzing GW150914. We also constrain, for the first time, the instantaneous frequency of the $(\ell, |m|)=(4,4)$ mode at merger to about $6\%$, and the time at which the gravitational-wave amplitude peaks to about $5~\mathrm{ms}$. These results are the most precise tests of general relativity in the nonlinear regime to date, and can be employed to constrain extensions of Einsten's theory.

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arXiv2026

Phenomenology and origin of late-time tails in eccentric binary black hole mergers

We investigate the late-time tail behavior in gravitational waves from merging eccentric binary black holes (BBH) using black hole perturbation theory. For simplicity, we focus only on the dominant quadrupolar mode of the radiation. We demonstrate that such tails become more prominent as eccentricity increases. Exploring the phenomenology of the tails in both spinning and non-spinning eccentric binaries, with the spin magnitude varying from $χ=-0.6$ to $χ=+0.6$ and eccentricity as high as $e=0.98$, we find that these tails can be well approximated by a slowly decaying power law. We study the power law for varying systems and find that the power law exponent lies close to the theoretically expected value $-4$. Finally, using both plunge geodesic and radiation-reaction-driven orbits, we perform a series of numerical experiments to understand the origin of the tails in BBH simulations. Our results suggest that the late-time tails are strongly excited in eccentric BBH systems when the smaller black hole is in the neighborhood of the apocenter, as opposed to any structure in the strong field of the larger black hole. Our analysis framework is publicly available through the \texttt{gwtails} Python package.

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arXiv2025

A Parametrized Test of General Relativity for LISA Massive Black Hole Binary Inspirals

Laser Interferometer Space Antenna (LISA) observations of massive black hole binaries (MBHBs) will provide long duration inspiral signals with high signal-to-noise ratio (SNR) data, ideal for testing general relativity (GR) in the strong-field and relativistic regime regime. We present an extension of the Flexible Theory-Independent (FTI) framework, adapted to gravitational waves (GWs) from MBHBs observed with LISA, to perform parametrized inspiral tests of GR. This approach introduces generic deviations to the post-Newtonian (PN) coefficients of the frequency-domain GW phase while accounting for the time- and frequency-dependent instrument response, thus effectively identifying potential deviations from GR by constraining modifications to the PN phasing formula. Complementary analyses using Fisher matrix and full Bayesian approaches confirm that LISA observations could improve constraints on agnostic, scale-independent deviations from GR by at least two orders of magnitude compared to the most recent LIGO-Virgo-KAGRA measurements. Since LISA's sensitivity to different GW phases -- inspiral, merger, and ringdown -- varies across the MBHB parameter space with masses between $10^4$ and $10^7M_{\odot}$, the optimal regime for testing agnostic deviations is not known a priori. Our results illustrate how the strength of these constraints depends significantly on both the total mass and the SNR, reflecting the trade-off between inspiral and merger-ringdown contributions to the observed signal. We also investigate the interplay between inspiral-only versus inspiral-merger-ringdown analyses in constraining these inspiral deviation parameters. This work contributes to the development of robust tests of GR with LISA, enhancing our ability to probe the nature of gravity and BHs with GW observations.

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arXiv2025

Highly accurate simulations of asymmetric black-hole scattering and cross validation of effective-one-body models

The study of unbound binary-black-hole encounters provides a gauge-invariant approach to exploring strong-field gravitational interactions in two-body systems, which can subsequently inform waveform models for bound orbits. In this work, we present 60 new highly accurate numerical relativity (NR) simulations of black-hole scattering, generated using the Spectral Einstein Code (SpEC). Our simulations include 14 spin-aligned configurations, as well as 16 configurations with unequal masses, up to a mass ratio of 10. We perform the first direct comparison of scattering angles computed using different NR codes, finding good agreement. We compare our NR scattering angle results to the post-Minkowskian (PM)-based effective-one-body (EOB) closed-form models SEOB-PM and $w_{\rm EOB}$, finding less than 5% deviation except near the scatter-capture separatrix. Comparisons with the post-Newtonian-based EOB evolution models SEOBNRv5 and TEOBResumS-Dalí reveal that the former agrees within 8% accuracy with non-spinning NR results across most parameter ranges, whereas the latter matches similarly at lower energies but diverges significantly at higher energies. Both evolution EOB models exhibit increased deviations for spinning systems, predicting a notably different location of the capture separatrix compared to NR. Our key result is the first measurement of disparate scattering angles from NR simulations due to asymmetric gravitational-wave emission. We compare these results to SEOB-PM models constructed to calculate the scattering angle of a single black hole in asymmetric systems.

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arXiv2025

Peaking into the abyss: Characterizing the merger of equatorial-eccentric-geodesic plunges in rotating black holes

We study the gravitational waveforms generated by critical, equatorial plunging geodesics of the Kerr metric that start from an unstable-circular-orbit, which describe the test-mass limit of spin-aligned eccentric black-hole mergers. The waveforms are generated employing a time-domain Teukolsky code. We span different values of the Kerr spin $-0.99 \le a \le 0.99 $ and of the critical eccentricity $e_c$, for bound ($0 \le e_c<1$) and unbound plunges ($e_c \ge 1$). We find that, contrary to expectations, the waveform modes $h_{\ell m}$ do not always manifest a peak for high eccentricities or spins. In case of the dominant $h_{22}$ mode, we determine the precise region of the parameter space in which its peak exists. In this region, we provide a characterization of the merger quantities of the $h_{22}$ mode and of the higher-order modes, providing the merger structure of the equatorial eccentric plunges of the Kerr spacetime in the test-mass limit.

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arXiv2025

Systematic Biases in Estimating the Properties of Black Holes Due to Inaccurate Gravitational-Wave Models

Gravitational-wave (GW) observations of binary black-hole (BBH) coalescences are expected to address outstanding questions in astrophysics, cosmology, and fundamental physics. Realizing the full discovery potential of upcoming LIGO-Virgo-KAGRA (LVK) observing runs and new ground-based facilities hinges on accurate waveform models. Using linear-signal approximation methods and Bayesian analysis, we start to assess our readiness for what lies ahead using two state-of-the-art quasi-circular, spin-precessing models: \texttt{SEOBNRv5PHM} and \texttt{IMRPhenomXPHM}. We ascertain that current waveforms can accurately recover the distribution of masses in the LVK astrophysical population, but not spins. We find that systematic biases increase with detector-frame total mass, binary asymmetry, and spin-precession, with most such binaries incurring parameter biases, extending up to redshifts $\sim3$ in future detectors. Furthermore, we examine three ``golden'' events characterized by large mass ratios, significant spin magnitudes, and high precession, evaluating how systematic biases may affect their scientific outcomes. Our findings reveal that current waveforms fail to enable the unbiased measurement of the Hubble-Lemaître parameter from loud signals, even for current detectors. Moreover, highly asymmetric systems within the lower BH mass-gap exhibit biased measurements of the secondary-companion mass, which impacts the physics of both neutron stars and formation channels. Similarly, we deduce that the primary mass of massive binaries ($ > 60 M_\odot$) will also be biased, affecting supernova physics. Future progress in analytical calculations and numerical-relativity simulations, crucial for calibrating the models, must target regions of the parameter space with significant biases to develop more accurate models. Only then can precision GW astronomy fulfill the promise it holds.

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arXiv2025

Modeling matter(s) in SEOBNRv5THM: Generating fast and accurate effective-one-body waveforms for spin-aligned binary neutron stars

We present SEOBNRv5THM, an accurate and fast gravitational-waveform model for quasi-circular, spinning, non-precessing binary neutron stars (BNS) within the effective-one-body (EOB) formalism. It builds on the binary-black-hole approximant SEOBNRv5HM and, compared to its predecessor SEOBNRv4T, it i) incorporates recent high-order post-Newtonian results in the inspiral, including higher-order adiabatic tidal contributions, spin-induced multipoles and dynamical tides for spin-aligned neutron stars, ii) includes the gravitational modes $(\ell, |m|)=(2,2),(3,3),(2,1),(4,4),(5,5),(3,2),$ and $(4,3)$, iii) has a time of merger calibrated to BNS numerical-relativity (NR) simulations, iv) accurately models the pre-merger $(2,2)$ mode through a novel phenomenological ansatz, and v) is 100 to 1000 times faster than its predecessor model for BNS systems with total mass $M \geq 2\, M_\odot$. Thus, SEOBNRv5THM can be used in Bayesian parameter estimation, which we perform for two BNS events observed by the LIGO-Virgo Collaboration, GW170817 and GW190425. The model accurately reproduces BAM and SACRA NR waveforms with errors comparable to or lower than the intrinsic NR uncertainty. We validate the model against the other state-of-the-art BNS waveform models NRTidalv3 and TEOBResumS and find differences only for highly spinning and highly tidally deformable BNS, where there is no NR coverage and the models employ different spin prescriptions. Our model serves as a foundation for the development of subsequent SEOBNR waveform models with matter that incorporate further effects, such as spin-precession and eccentricity, to be employed for upcoming observing runs of the LIGO-Virgo-KAGRA Collaboration and future facilities on the ground.

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arXiv2025

Inspiral-merger-ringdown waveforms with gravitational self-force results within the effective-one-body formalism

Gravitational self-force (GSF) theory is a strong-gravity perturbative approach to the relativistic two-body problem, primarily developed to model extreme-mass-ratio inspirals, where one compact object is significantly more massive than the companion. However, recent advancements in GSF calculations, particularly involving second-order self-force (2GSF) results, indicated a much broader applicability across a wider range of mass ratios. These developments have motivated efforts to incorporate GSF results into the effective-one-body (EOB) framework, where they have already been successfully integrated into the state-of-the-art waveform model, SEOBNRv5, employed in recent LIGO-Virgo-KAGRA (LVK) observing runs. In this work, we present SEOBNR-GSF, a nonspinning inspiral-merger-ringdown (IMR) EOB waveform model that introduces a GSF-informed EOB Hamiltonian as its central innovation. This marks the first complete IMR waveform model constructed primarily from GSF results. We show that our model outperforms inspiral waveforms from full 2GSF calculations in the intermediate-to-comparable mass regime. Furthermore, by comparing with a post-Newtonian-informed variant, SEOBNR-GSF-PN, we demonstrate that the inclusion of numerical GSF information in the Hamiltonian leads to significant improvements in model fidelity. Finally, we benchmark our model against high-accuracy, nonspinning numerical-relativity simulations from the Simulating eXtreme Spacetimes (SXS) catalogue and find that its median mismatch is comparable to that of SEOBNRv5, suggesting that this approach holds promise for further enhancing future EOB waveform models.

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arXiv2025

The Science of the Einstein Telescope

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

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arXiv2025

Accounting for numerical-relativity calibration uncertainty in gravitational-wave modeling and inference

The increasing sensitivity of current and upcoming gravitational-wave (GW) detectors poses stringent requirements on the accuracy of the GW models used for data analysis. If these requirements are not met, systematic errors could dominate over statistical uncertainties, hindering our ability to extract astrophysical and cosmological information, and conduct precise tests of General Relativity. In this work, we present a novel method to mitigate the impact of waveform-systematic errors, by incorporating and marginalizing over waveform-uncertainty estimates, which are modeled as probability distributions for the numerical-relativity calibration parameters of effective-one-body waveform models. By analyzing simulated GW signals of loud ``golden'' binary-black-hole systems, we show that our method significantly reduces biases in the recovered parameters, highlighting its potential to improve the robustness of GW parameter estimation with upcoming observing runs and next-generation ground-based facilities, such as the Einstein Telescope and Cosmic Explorer.

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arXiv2025

Accurate waveforms for eccentric, aligned-spin binary black holes: The multipolar effective-one-body model SEOBNRv5EHM

The measurement of orbital eccentricity in gravitational-wave (GW) signals will provide unique insights into the astrophysical origin of binary systems, while ignoring eccentricity in waveform models could introduce significant biases in parameter estimation and tests of General Relativity. Upcoming LIGO-Virgo-KAGRA observing runs are expected to detect a subpopulation of eccentric signals, making it vital to develop accurate waveform models for eccentric orbits. Here, employing recent analytical results through the third post-Newtonian order, we develop SEOBNRv5EHM: a new time-domain, effective-one-body, multipolar waveform model for eccentric binary black holes with spins aligned (or antialigned) with the orbital angular momentum. Besides the dominant (2,2) mode, the model includes the (2,1), (3,3), (3,2), (4,4) and (4,3) modes. We validate the model's accuracy by computing its unfaithfulness against 99 (28 public and 71 private) eccentric numerical-relativity (NR) simulations, produced by the Simulating eXtreme Spacetimes Collaboration. Importantly, for NR waveforms with initial GW eccentricities below 0.5, the maximum (2,2)-mode unfaithfulness across the total mass range 20-200 $M_\odot$ is consistently below or close to $1 \%$, with a median value of $ \sim 0.02 \% $, reflecting an accuracy improvement of approximately an order of magnitude compared to the previous-generation SEOBNRv4EHM and the state-of-the-art TEOBResumS-Dalí eccentric model. In the quasi-circular-orbit limit, SEOBNRv5EHM is in excellent agreement with the highly accurate SEOBNRv5HM model. The accuracy, robustness, and speed of SEOBNRv5EHM make it suitable for data analysis and astrophysical studies. We demonstrate this by performing a set of recovery studies of synthetic NR-signal injections, and parameter-estimation analyses of the events GW150914 and GW190521, which we find to have no eccentricity signatures.

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arXiv2025

Third post-Newtonian dynamics for eccentric orbits and aligned spins in the effective-one-body waveform model SEOBNRv5EHM

Accurate waveform models for coalescing binaries on eccentric orbits are crucial for avoiding biases in the analysis of eccentric gravitational-wave signals. The effective-one-body (EOB) formalism combines various analytical approximation methods with information derived from numerical-relativity simulations, and it has proven reliable in modeling the inspiral-merger-ringdown waveform of binaries on generic orbits. In this work, we derive new analytical results within the EOB formalism, specifically addressing eccentric, aligned-spin binaries. For the first time, we obtain EOB results for eccentric orbits that are accurate up to the third post-Newtonian (PN) order for the complete far-zone energy and angular-momentum fluxes, the radiation-reaction (RR) force, and waveform modes (including memory contributions). We obtain these results by deriving transformations from the harmonic to EOB coordinates and from the quasi-Keplerian to the Keplerian parametrization, that properly account for the spin-supplementary condition, post-adiabatic contributions, and the gauge freedom in the RR force. We employ these findings to build the inspiral part of the SEOBNRv5EHM waveform model, which includes the 3PN eccentricity contributions in the RR force and waveform modes using the Keplerian parametrization, and augments the EOB equations of motion with PN evolution equations for the Keplerian parameters. The new SEOBNR model achieves much better accuracy than its predecessor SEOBNRv4EHM and other eccentric models, even for eccentricities as high as $\lesssim 0.5$.

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arXiv2025

Impact of eccentricity and mean anomaly in numerical relativity mergers

Accurate modelling of black hole binaries is critical to achieve the science goals of gravitational-wave detectors. Modelling such configurations relies strongly on calibration to numerical-relativity (NR) simulations. Binaries on quasi-circular orbits have been widely explored in NR, however, coverage of the broader 9-dimensional parameter space, including orbital eccentricity, remains sparse. This article develops a new procedure to control orbital eccentricity of binary black hole simulations that enables choosing initial data parameters with precise control over eccentricity and mean anomaly of the subsequent evolution, as well as the coalescence time. We then calculate several sequences of NR simulations that nearly uniformly cover the 2-dimensional eccentricity--mean anomaly space for equal mass, non-spinning binary black holes. We demonstrate that, for fixed eccentricity, many quantities related to the merger dynamics of binary black holes show an oscillatory dependence on mean anomaly. The amplitude of these oscillations scales nearly linearly with the eccentricity of the system. We find that for the eccentricities explored in this work, the magnitude of deviations in various quantities such as the merger amplitude and peak luminosity can approach $\sim5\%$ of their quasi-circular value. We use our findings to explain eccentric phenomena reported in other studies. We also show that methods for estimating the remnant mass employed in the effective-one-body approach exhibit similar deviations, roughly matching the amplitude of the oscillations we find in NR simulations. This work is an important step towards a complete description of eccentric binary black hole mergers, and demonstrates the importance of considering the entire 2-dimensional parameter subspace related to eccentricity.

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arXiv2025

The fault in our sirens: Hierarchical diagnosis of waveform systematics in Hubble-Lemaître constant measurements

Cosmological inference using a population of binary black-hole mergers, combined with a galaxy catalog, presents an exciting opportunity for precision cosmology with the possibility of resolving the Hubble tension. However, the accuracy of these measurements heavily relies on the quality of the model used to infer the binary parameters, including the model of the gravitational-wave signal. We use state-of-the-art waveform models to explore the impact of inaccurate modeling in measuring the Hubble-Lemaître constant for the upcoming and future ground-based gravitational-wave observatories. We diagnose the presence of inaccuracies within a hierarchical population-analysis framework, without a priori knowing the true value of the parameter, by assessing the consistency of the distribution of individual posteriors in relation to their measurement errors. Our findings indicate that even a small high-mass, spin-precessing subpopulation -- comprising as little as 5\% of the population generating the events observed by the LIGO-Virgo-KAGRA Collaboration so far -- can result in an unreliable measurement of the Hubble-Lemaître constant in the upcoming observing runs of these detectors, with even more pronounced effects expected in future facilities on the ground.

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arXiv2025

Parametrized spin-precessing inspiral-merger-ringdown waveform model for tests of general relativity

The coalescence of binary black holes (BBHs) provides a unique arena to test general relativity (GR) in the dynamical, strong-field regime. To this end, we present pSEOBNRv5PHM, a parametrized, multipolar, spin-precessing waveform model for BBHs in quasicircular orbits, built within the effective-one-body formalism. Compared to its predecessor, pSEOBNRv4HM, our model introduces parametrized deviations from GR not only in the plunge-merger-ringdown stages, but also in the inspiral phase through modifications to the conservative dynamics. Additionally, it incorporates, for the first time, spin-precession effects. The free deviation parameters can be used to perform null tests of GR using current and future gravitational-wave observations. We validate pSEOBNRv5PHM through Bayesian parameter estimation, focusing on the quasinormal-mode frequency and damping time of the $(\ell,m,n) = (2,2,0)$ mode. Our analysis of synthetic signals from numerical-relativity (NR) simulations of highly precessing BH mergers shows that, while pSEOBNRv5PHM correctly recovers consistency with GR, neglecting spin precession can lead to false detections of deviations from GR even at current detector sensitivity. Conversely, when analyzing a synthetic signal from a NR simulation of a binary boson-star merger, the model successfully identifies a deviation from a GR BBH signal. Finally, we reanalyze 12 events from the third Gravitational-Wave Transient Catalog. Using a hierarchical combination of these events, we constrain fractional deviations in the frequency and damping time of the $(2,2,0)$ quasinormal-mode to $δf_{220}=0.00_{-0.06}^{+0.06}$ and $δτ_{220}=0.15_{-0.24}^{+0.26}$ at 90% credibility. These results are consistent with those from the LIGO-Virgo-KAGRA Collaboration, which did not account for spin-precession effects.

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arXiv2025

Testing eccentric corrections to the radiation-reaction force in the test-mass limit of effective-one-body models

In this work, we test an effective-one-body radiation-reaction force for eccentric planar orbits of a test mass in a Kerr background, which contains third-order post-Newtonian (PN) non-spinning and second-order PN spin contributions. We compare the analytical fluxes connected to two different resummations of this force, truncated at different PN orders in the eccentric sector, with the numerical fluxes computed through the use of frequency- and time-domain Teukolsky-equation codes. We find that the different PN truncations of the radiation-reaction force show the expected scaling in the weak gravitational-field regime, and we observe a fractional difference with the numerical fluxes that is $<5 \%$, for orbits characterized by eccentricity $0 \le e \le 0.7$, central black-hole spin $-0.99 M \le a \le 0.99 M$ and fixed orbital-averaged quantity $x=\langle MΩ\rangle^{2/3} = 0.06$, corresponding to the mildly strong-field regime with semilatera recta $9 M<p<17 M$. Our analysis provides useful information for the development of spin-aligned eccentric models in the comparable-mass case.

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