arXiv subjects

Rossella Gamba

Publications and source records attributed to Rossella Gamba.

At least 19 recordsLinked to original sources

arXiv2026

Spin the black circle II: tidal heating and torquing of a rotating black hole by a test mass on generic orbits

Horizon fluxes of energy and angular momentum are a key strong-field effect in the dynamics of black holes, encoding direct information about their nature. In this work, we present a numerical study of these fluxes for a test particle orbiting a Kerr black hole on equatorial geodesics, covering circular, eccentric, and hyperbolic trajectories across a wide range of orbital parameters and black hole spins. We reproduce known results for circular orbits and uncover a richer phenomenology for eccentric and hyperbolic ones: the instantaneous fluxes can exhibit multiple peaks and sign changes, indicating a complex interplay between superradiant and non-superradiant regimes. We then compare these results against existing analytical post-Newtonian expressions, exploring resummation strategies to improve their performance against numerical data. In particular, we propose a factorized and resummed representation of the horizon fluxes that predicts the onset frequency of the superradiant regime to within $10\%$ for $\gtrsim 73\%$ of configurations for both the energy and angular momentum fluxes. This representation exactly reduces to the circular limit by construction, independently of the perturbative order of the remaining analytical terms. For peak and orbit-averaged fluxes, the analytical models achieve acceptable accuracy -- with relative errors at the $10\%$ level or below -- at large separations and low eccentricities. However, they can exhibit deviations of $\sim \mathcal{O}(100\%)$ in the strong-field regime, motivating the need for improved flux prescriptions and further investigations.

gr-qc↗

arXiv2026

The Cost of Circularity: Quantifying Eccentricity-Induced Biases in Binary Black Hole Inference

Dynamically assembled binary black holes are expected to retain measurable orbital eccentricity in the LIGO-Virgo-KAGRA band, but most parameter estimation analyses still assume quasi-circular inspirals. This raises a critical question: how strongly does unmodeled eccentricity bias the inferred properties of BBH mergers? We address this by injecting eccentric signals generated with TEOBResumS-Dali and recovering them using the circular, precessing IMRPhenomXPHM waveform model. Across $20$-$80 \, M_\odot$ and eccentricities up to $e=0.5$, we find that circular waveform models remain reliable only for very small eccentricities. Above $e\sim0.2$ at 10 Hz, recovered masses, spins, inclination, and distances begin to show significant systematic offsets. Circular precessing templates mimic eccentric amplitude and phase modulations by introducing artificial precession, highlighting a major degeneracy between these effects. For high-mass, moderately eccentric mergers, circular models misestimate parameters at a level that would bias astrophysical interpretation and population studies. Our results establish the parameter-space boundaries where eccentric waveform models become essential for accurate inference in current and next-generation detectors.

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arXiv2025

From Source Properties to Strong-Field Tests: a multipronged analysis of GW250114 with an effective one-body model for generic orbits

We present a detailed analysis of GW250114, the loudest gravitational-wave signal observed to date, using a waveform model capable of describing binary black holes in generic (eccentric and precessing) orbits. Our analysis builds on LIGO-Virgo-KAGRA (LVK)'s results, finding that the source is consistent at a probability of $\geq 96\%$ with the merger of two first-generation, nearly equal-mass, low-spin black holes, forming a remnant within the pair-instability mass gap. The signal's high signal-to-noise ratio ($\gtrsim 75$) enables the detection of the subdominant $(4,\pm4)$ multipoles, whose presence we confirm with higher evidence than previously reported by the LVK. Restricting the analysis even to post-peak data yields $\log_{10}B\gtrsim 1$ in favor of models including the $(4,\pm4)$ mode, demonstrating that this contribution remains detectable well into the post-merger phase. We further perform three independent tests of general relativity, complementary to those performed by the LVK: a modified residual analysis confirms that our semi-analytical model fully describes the signal without detectable discrepancies; a subdominant mode test finds that the amplitude of the $(4,\pm4)$ multipoles agrees with general-relativistic expectations; and a parameterised analysis of the plunge-merger-ringdown regime recovers the GR expectation within the 50\% credible region for the remnant mass and spin, and within the 90\% interval for the $(2,\pm2)$ peak amplitude. Collectively, these results reinforce GW250114 as a landmark event for a precision test of gravity.

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arXiv2025

A parametrized model for gravitational waves from eccentric, precessing binary black holes: theory-agnostic tests of General Relativity with pTEOBResumS

Gravitational waves from binary black hole (BBH) mergers allow us to test general relativity in the strong-field, high-curvature regime. However, existing gravitational wave-based tests have so far assumed non-eccentric signal sources, limiting their applicability to more general astrophysical scenarios. In this work, we present pTEOBResumS, a new parametrized inspiral-merger-ringdown model for null tests of GR that incorporates both orbital eccentricity and spin precession. Building on the effective-one-body model TEOBResumS-Dalí, we introduce parametrized deviations from GR both in the inspiral and the merger-ringdown regimes. We validate the model via parameter estimation of synthetic signals, including from numerical relativity simulations of BBHs and a boson star binary. These allow us to establish the model's consistency, demonstrate its capability to identify beyond-GR effects, and gauge the impact of eccentricity in tests of GR. We then analyze a set of BBH events from the first three LIGO-Virgo-KAGRA observing runs, testing whether they are best explained by a GR or non-GR waveform, under either the eccentric, spin-aligned or precessing, quasi-circular hypotheses. We find no significant statistical evidence in favor of deviations from GR. Consistent with previous works, we infer a mild preference for longer remnant quasi-normal mode damping times than expected in GR, though the limited sample and potential systematics reduce its significance. In addition, when weighting by signal strength, joint posteriors combining the individual events are still compatible with GR. We find no strong evidence for imprints of orbital eccentricity in the analyzed events, with the exception of GW200129. For this, our analysis finds a strong preference for an eccentric, GR-consistent description, although as previous works have noted this result could be influenced by data quality issues.

gr-qc↗

arXiv2025

Gravitational waves from eccentric binary neutron star mergers: Systematic biases and inadequacy of quasicircular templates

The use of quasicircular waveforms in matched-filter analyses of signals from eccentric binary neutron star mergers can lead to biases in the source's parameter estimation. We demonstrate that significant biases can be present already for moderate eccentricities $e_{0} \gtrsim 0.05$ and signals detected by LIGO-Virgo-KAGRA with signal-to-noise ratio $\gtrsim 12$. We perform systematic Bayesian mock analyses of unequal-mass nonspinning binary neutron star signals up to eccentricities $e_0 \sim 0.1$ using quasicircular effective-one-body waveforms with spins. We find fractional signal-to-noise ratio losses up to tens of percent and up to 16$σ$ deviations in the inference of the chirp mass. The latter effect is sufficiently large to lead to an incorrect (and ambiguous) source identification. The inclusion of spin precession in the quasicircular waveform does not capture eccentricity effects. We conclude that high-precision observations with advanced (and next generation) detectors are likely to require standardized, accurate, and fast eccentric waveforms.

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arXiv2025

$\texttt{GR-Athena++}$ Simulations of Spinning Binary Black Hole Mergers

We present the second release of the $\texttt{GR-Athena++}$ waveform catalog, comprising four new quasi-circular, non-precessing, spinning binary black hole simulations. These simulations are performed at high resolutions and represent a step toward generating high-fidelity gravitational waveforms that can eventually meet the accuracy requirements of upcoming next-generation detectors, including LISA, Cosmic Explorer, and Einstein Telescope. Gravitational waves are extracted at future null infinity ( $\mathscr{I}^{+}$) using both Cauchy characteristic extraction and finite-radius extraction. For each simulation, we provide strain data across multiple resolutions and analyze waveform accuracy via convergence studies and self-mismatch analyses. The absolute phase and relative amplitude differences reach their largest values near the merger, while the smallest errors are of order $\mathscr{O}(10^{-2})$ and $\mathscr{O}(10^{-3})$, respectively. A self-mismatch analysis of the dominant $(2,2)$ mode yields mismatches between $\mathscr{O}(10^{-5})$ and $\mathscr{O}(10^{-7})$ for a total binary mass of $10^{6}$ $M_{\odot}$ over the frequency range $[0.002, 0.1]$ Hz using LISA noise curve. All waveforms are publicly available via $\texttt{ScholarSphere}$.

gr-qc↗

arXiv2025

Binary black hole merger in the extreme mass ratio limit: a multipolar analysis of the inclined orbit case

We compute the gravitational waveform emitted during the transition from quasi-spherical inspiral to plunge, merger and ringdown for a system of two black holes in the extreme mass ratio limit, where the primary is spinning and the secondary is represented by a nonspinning point-particle inspiralling along inclined orbits. The point-particle dynamics is described via a Hamiltonian formalism and the transition is driven by an effective-one-body like radiation reaction force. The gravitational waveform is obtained solving numerically, in the time-domain, the Teukolsky equation with a $δ$-like source. The waveform is systematically characterized varying the black hole spin magnitude between $(0,0.9)$ and the inclination angle of the orbit between $(0,π)$. We consider all multipoles up to $\ell=4$ and compute the energy and angular momentum losses during the plunge. The impact of the $m\neq \ell$ modes grows as the inclination angle is increased. We also use our framework to quantify the accuracy of the approximate inspiral-merger-ringdown waveform for an inclined orbit that can be obtained by applying a suitable time-dependent rotation to a given spin-aligned waveform with approximately consistent (but constant) spin-orbit coupling.

gr-qc↗

arXiv2025

Revisiting GW150914 with a non-planar, eccentric waveform model

The first direct detection of gravitational waves by the LIGO collaboration, GW150914, marked the start of a new exciting era in astronomy, enabling the study of the Universe through a new messenger. Since then, the field has grown rapidly, with the development of increasingly more sophisticated techniques to detect, analyze and interpret the signals. In this paper we revisit GW150914, presenting updated estimates of its source parameters using a waveform model developed within the EOB formalism, able to describe gravitational-wave emission from generic non-circular, non-planar binaries. We provide a comprehensive analysis of the signal and its properties, considering and contrasting various scenarios for the source: from the simplest, aligned-spin quasi-circular binary black hole merger, to more complex scenarios, including precession, eccentricity or both. Unsurprisingly, we find that the signal is consistent with a quasi-circular ($e < 0.08$ at $15$ Hz), slowly spinning $(χ_{\rm eff} = -0.03^{+0.12}_{-0.13})$ binary black hole merger, a-posteriori validating a considerable body of works. This is the first analysis performed with an inspiral-merger-ringdown model containing both eccentricity and precession.

gr-qc↗

arXiv2025

AthenaK simulations of the binary black hole merger GW150914

We present new binary black hole simulations targeted to GW150914 using the GPU-accelerated code AthenaK. We compute the properties of the final remnant with the isolated horizon formalism and obtain gravitational-waveforms at future null infinity via Cauchy characteristic extraction. We compare our results with those obtained by the Simulating eXtreme Spacetimes (SXS) and Rochester Institute of Technology (RIT) groups, targeted to the same event. We find excellent agreement with the SXS and RIT results in the remnant mass, spin, and recoil velocity. For the dominant $(\ell,m)=(2,2)$ mode of the gravitational-wave signal we find maximum dephasing of $Δϕ\simeq 0.35$ and amplitude difference of $ΔA/A \simeq 0.4\%$. We use our newly computed waveform to re-analyze the GW150914 data and find posteriors for chirp mass, luminosity distance, and inclination that are broadely consistent with those obtained using semi-analytic waveform models. This work demonstrates the viability of AthenaK for many-orbits binary black hole merger simulations. A step-by-step tutorial, including all necessary input files and analysis scripts to reproduce our results, is available on GitHub.

gr-qc↗

arXiv2025

Kilohertz Gravitational Waves from Binary Neutron Star Mergers: Full Spectrum Analyses and High-density Constraints on Neutron Star Matter

We demonstrate Bayesian analyses of the complete gravitational-wave spectrum of binary neutron star mergers events with the next-generation detector Einstein Telescope. Our mock analyses are performed for 20 different signals using the TEOBResumSPA_NRPMw waveform that models gravitational-waves from the inspiral to the postmerger phase. They are employed to validate a pipeline for neutron star's extreme matter constraints with prospective detections and under minimal hypotheses on the equation of state. The proposed analysis stack delivers inferences for the mass-radius curve, the mass dependence of the quadrupolar tidal polarizability parameter, the neutron star's maximum density, the maximum mass and the relative radius, and the pressure-density relation itself. We show that a single event at a signal-to-noise ratio close to the minimum threshold for postmerger detection is sufficient to tightly constrain all the above relations as well as quantities like the maximum mass (maximum density) to precision of ${\sim}6$% (${\sim}10$%) at 90% credibility level. We also revisit inferences of prompt black hole formation with full spectrum signals and find that the latter can be robustly identified, even when the postmerger is not detectable due to a low signal-to-noise ratio. New results on the impact of the initial signal frequency and of the detector configuration (triangular vs. two-L) on the source's parameters estimation are also reported. An improvement of approximately one order of magnitude in the precision of the chirp mass and mass ratio can be achieved by lowering the initial frequency from 20 Hz to 2 Hz. The two-L configuration shows instead significant improvements on the inference of the source declination, due to geographical separation of the two detectors.

gr-qc↗

arXiv2025

Black-hole - neutron-star mergers: new numerical-relativity simulations and multipolar effective-one-body model with spin precession and eccentricity

In this paper, we present 52 new numerical-relativity (NR) simulations of black-hole-neutron-star merger (BHNS) mergers and employ the data to inform TEOBResumS-Dal\'i: a multipolar effective-one-body model also including precession and eccentricity. Our simulations target quasicircular mergers and the parameter space region characterized by significant tidal disruption of the star. Convergent gravitational waveforms are produced with a detailed error budget after extensive numerical tests. We study in detail the multipolar amplitude hierarchy and identify a characteristic tidal signature in the $(\ell,m)=(2,0)$, and $(3,0)$ modes. We also develop new NR-informed models for the remnant black hole and for the recoil velocity. The numerical data is then used to inform next-to-quasicircular corrections and the ringdown of TEOBResumS-Dal\'i for BHNS. We show an overall order of magnitude improvement in the waveform's amplitude at merger and more consistent multipoles over our older TEOBResumS-GIOTTO for BHNS. TEOBResumS-Dal\'i is further validated with a new 12 orbit precessing simulation, showing phase and relative amplitude differences below $\sim 0.5$ (rad) throughout the inspiral. The computed mismatches including all the modes lie at the one percent level for low inclinations. Finally, we demonstrate for the first time that TEOBResumS-Dal\'i can produce robust waveforms with both eccentricity and precession, and use the model to identify the most urgent BHNS to simulate for waveform development. Our new numerical data are publicly released as part of the CoRe database.

gr-qc↗

arXiv2025

Binary Black Hole Waveforms from High-Resolution GR-Athena++ Simulations

The detection and subsequent inference of binary black hole signals rely heavily on the accuracy of the waveform model employed. In the highly non-linear, dynamic, and strong-field regime near merger, these waveforms can only be accurately modeled through numerical relativity simulations. Considering the precision requirements of next-generation gravitational wave observatories, we present in this paper high-resolution simulations of four non-spinning quasi-circular binary black hole systems with mass ratios of 1, 2, 3, and 4, conducted using the GR-Athena++ code. We extract waveforms from these simulations using both finite radius and Cauchy characteristic extraction (CCE) methods. Additionally, we provide a comprehensive error analysis to evaluate the accuracy and convergence of the waveforms. Our self-mismatch study shows that the (2, 2) mode of the CCE strains, for the world tube extraction radius of $R=50$, reaches the level of ${\sim} 10^{-12}$ mismatch for mass ratios of 1, 2, 3, and ${\sim} 10^{-11}$ mismatch for the mass ratio of 4. However, when larger extraction radii are considered or when more modes are included the mismatches increase. These results highlight both the promise and limitations of current simulations in achieving the precision required for upcoming detectors such as LISA, Cosmic Explorer, and Einstein Telescope. The waveforms are publicly available on ScholarSphere, and represent the first set of waveforms of the new GR-Athena++ catalog.

gr-qc↗

arXiv2025

Effective-one-body modeling for generic compact binaries with arbitrary orbits

We present the first unified model for the general relativistic dynamics and gravitational radiation of generic compact binaries. TEOBResumS-Dalí is a model based on the effective-one-body framework incorporating tidal interactions, generic spins, multipolar radiation reaction/waveform and numerical-relativity information. It allows the computation of gravitational waves and other dynamical gauge invariants from generic binaries (black holes, neutron stars, neutron star-black hole binaries) evolving along arbitrary orbits (quasi-circular, eccentric, non-planar) through merger and including scattering. The performances of TEOBResumS-Dalí in the strong-field regime are showcased by comparisons with a large sample of 1395 high-accuracy numerical-relativity simulations available. TEOBResumS-Dalí allows the computation of faithful waveforms for gravitational wave astronomy, providing at the same time an understanding and a prediction of the strong-field dynamics.

gr-qc↗

arXiv2025

Scattering and dynamical capture of two black holes: synergies between numerical and analytical methods

We study initially unbound systems of two black holes using numerical relativity (NR) simulations performed with GR-Athena++. We focus on regions of the parameter space close to the transition from scatterings to dynamical captures, considering equal mass and spin-aligned configurations, as well as unequal mass and nonspinning ones. The numerical results are then used to validate the effective-one-body (EOB) model TEOBResumS-Dalí for dynamical captures and scatterings. We find good agreement for the waveform phenomenologies, scattering angles, mismatches, and energetics in the low energy regime ($E_0\lesssim 1.02\,M$). In particular, mismatches weighted with the zero-detuned, high-power noise spectral density of Advanced LIGO are typically below or around the $1\%$ level, with only a few cases, corresponding to spinning binaries, slightly above the $3\%$ threshold, thus suggesting the usability of TEOBResumS-Dalí for current data analysis of low-energy scatterings and dynamical captures. We also discuss dynamical captures in the test-mass limit by solving numerically the Zerilli equation with the time domain code RWZHyp. The latter analysis provides valuable insights into both the analytical noncircular corrections of the EOB waveform and the integration of NR Weyl scalars.

gr-qc↗

arXiv2025

Cosmic Calipers: Precise and Accurate Neutron Star Radius Measurements with Next-Generation Gravitational Wave Detectors

Gravitational waves from merging binary neutron stars carry characteristic information about their astrophysical properties, including masses and tidal deformabilities, that are needed to infer their radii. In this study, we use Bayesian inference to quantify the precision with which radius can inferred with upgrades in the current gravitational wave detectors and next-generation observatories such as the Einstein Telescope and Cosmic Explorer. We assign evidences for a set of plausible equations of state, which are then used as weights to obtain radius posteriors. We find that prior choices and the loudness of observed signals limit the precision and accuracy of inferred radii by current detectors. In contrast, next-generation observatories can resolve the radius precisely and accurately, across most of the mass range to within $\lesssim 5\%$ for both soft and stiff equations of state. We also explore how the choice of the neutron star mass prior can influence the inferred masses and potentially affect radii measurements, finding that choosing an astrophysically motivated prior does not notably impact an individual neutron star's radius measurements.

astro-ph.HE↗

arXiv2025

Effective-one-body waveform model for noncircularized, planar, coalescing black hole binaries II:high accuracy by improving logarithmic terms in resummations

Effective-one-body (EOB) models are based on analytical building blocks that, mathematically, are truncated Taylor series with logarithms. These functions are usually resummed using Padé approximants obtained first assuming that the logarithms are constant, and then replacing them back into the resulting rational functions. A recent study pointed out that this procedure introduces spurious logarithmic terms when the resummed functions are reexpanded. Here we update the TEOBResumS-Dalí waveform model for spin-aligned, noncircularized coalescing black hole binaries by systematically implementing new (still Padé based) resummations for all EOB functions (that is, the metric potentials $A, D$ and the residual waveform amplitude corrections $ρ_{\ell m}$ up to $\ell=8$). Once the model is informed by 50 Numerical Relativity simulations, this new approach proves key in lowering the maximum EOB/NR unfaithfulness $\bar{F}_{\rm EOBNR}^{\rm max}$ for the $\ell=m=2$ mode (with the Advanced LIGO noise in the total mass range $10-200M_{\odot}$) over 530 spin-aligned waveforms of the Simulating eXtreme Spacetimes catalog. A median unfaithfulness equal to $3.09\times 10^{-4}$ is achieved, which is a marked improvement over the previous value, $1.06\times 10^{-3}$. The largest value, ${\rm Max}[\bar{F}^{\rm max}_{\rm EOBNR}]= 6.80\times 10^{-3}$, is found for an equal-mass, equal-spin simulation with dimensionless spins $\sim +0.998$; only five configurations have $\bar{F}^{\rm max}_{\rm EOBNR} > 5\times 10^{-3}$ (four of which equal-mass and with equal spins larger than $\sim +0.98$). Results for eccentric binaries are similarly excellent (well below $10^{-2}$ and mostly around $10^{-3}$).

gr-qc↗

arXiv2024

Spin the black circle: horizon absorption on non-circular, planar binary black hole dynamics

Binary systems of black holes emit gravitational waves as they move through their orbits. While most of the emitted radiation escapes to future null infinity, a small fraction is absorbed by the black holes themselves. This is known as horizon absorption or tidal heating/torquing, and causes the black holes' masses and spins to change as the system evolves. In this work, we quantify the effects of the horizon fluxes on binary black hole dynamics by computing them up to next-to-next-to-leading order on generic planar orbits, also exploring physically motivated factorizations of the results. We integrate these fluxes over unbound, hyperbolic-like trajectories obtained with the Effective-One-Body model TEOBResumS-Dalí. We discuss the resulting phenomenology across a sizable slice of the relevant parameter space, finding a very small effect in most cases, except on highly energetic orbits. However, the predicted mass and spin variations are quantitatively and qualitatively very sensitive to the analytical representation chosen for the fluxes in that regime. We then perform comparisons with numerical relativity data of induced spins from hyperbolic encounters of initially nonrotating black holes, finding that the next-to-next-to-leading order factorized expressions we derive are crucial to reproduce the data. An optimization on the initial conditions (energy, angular momentum) is necessary for this, however, with differences of up to 9% between the numerical and optimal initial data. Finally, we use our analytical expressions to model possible astrophysical implications for black holes in globular clusters.

gr-qc↗

arXiv2024

Effective-one-body waveform model for non-circularized, planar, coalescing black hole binaries: the importance of radiation reaction

We present an updated version of the TEOBResumS-Dali effective-one-body (EOB) waveform model for spin aligned binaries on non-circularized orbits. Recently computed 4PN (nonspinning) terms are incorporated in the waveform and radiation reaction. The model is informed by a restricted sample ($\sim60$) of spin-aligned, quasi-circular, Numerical Relativity (NR) simulations. In the quasi-circular limit, the model displays EOB/NR unfaithfulness ${\bar{F}}^{\rm max}_{\rm EOBNR}\lesssim 10^{-2}$ (with median~ $1.06\times 10^{-3}$) (with Advanced LIGO noise and in the total mass range $10-200M_\odot$) for the dominant $\ell=m=2$ mode all over the 534 spin-aligned configurations available through the Simulating eXtreme Spacetime catalog of NR waveforms. Similar figures are also obtained with the 28 public eccentric SXS simulations and good compatibility between EOB and NR scattering angles is found. The quasi-circular limit of TEOBResumS-Dali is also found to be highly consistent with the TEOBResumS-GIOTTO quasi-circular model. We then systematically explore the importance of NR-tuning {\it also} the radiation reaction of the system. When this is done, the median of the distribution of quasi-circular ${\bar{F}}^{\rm max}_{\rm EOBNR}$ is lowered to $3.92\times 10^{-4}$, though balanced by a tail up to $\sim 0.1$ for large, positive spins. The same is true for the eccentric-inspiral datasets. We conclude that an improvement of the analytical description of the spin-dependent flux (and its interplay with the conservative part) is likely to be the cornerstone to lower the EOB/NR unfaithfulness below the $10^{-4}$ level all over the parameter space, thus grazing the current NR uncertainties as well as the expected needs for next generation of GW detector like Einstein Telescope.

gr-qc↗