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1. Efficient waveforms for asymmetric-mass eccentric equatorial inspirals into rapidly spinning black holes

   https://doi.org/10.1103/scbp-75pf  

   Chapman-Bird, Christian_E A; Speri, Lorenzo; Nasipak, Zachary; Burke, Ollie; Katz, Michael L; Santini, Alessandro; Kejriwal, Shubham; Lynch, Philip; Mathews, Josh; Khalvati, Hassan; et al (November 2025, Physical Review D)

   Observations of gravitational-wave signals emitted by compact binary inspirals provide unique insights into their properties, but their analysis requires accurate and efficient waveform models. Intermediate- and extreme-mass-ratio inspirals (I/EMRIs), with mass ratios $q\gtrsim {10}^2$ , are promising sources for future detectors such as the Laser Interferometer Space Antenna (LISA). Modeling waveforms for these asymmetric-mass binaries is challenging, entailing the tracking of many harmonic modes over thousands to millions of cycles. The FastEMRIWaveforms () modeling framework addresses this need, leveraging precomputation of mode data and interpolation to rapidly compute adiabatic waveforms for eccentric inspirals into zero-spin black holes. In this work, we extend to model eccentric equatorial inspirals into black holes with spin magnitudes $\left|a\right|\le 0.999$ . Our model supports eccentricities $e\le 0.9$ and semilatus recta $p\le 200$ , enabling the generation of long-duration IMRI waveforms, and produces waveforms in $\sim 100\mathrm{ms}$ with hardware acceleration. Characterizing systematic errors, we estimate that our model attains mismatches of $\sim {10}^{-5}$ (for LISA sensitivity) with respect to error-free adiabatic waveforms over the majority of the parameter space. We find that kludge models can introduce errors in signal-to-noise ratios (SNRs) as great as ${}_{-40\%}^{+60\%}$ and induce marginal biases of up to $\sim 1\sigma$ in parameter estimation. We show that LISA’s horizon redshift for I/EMRI signals varies significantly with $a$ , reaching a redshift of 3 (15) for EMRIs (IMRIs) with only minor $(\sim 10\%)$ dependence on $e$ for an SNR threshold of 20. For signals with $\mathrm{SNR}\sim 50$ , spin and eccentricity at plunge are measured with uncertainties of $\delta a\sim {10}^{-7}$ and $\delta e_{\mathrm{f}}\sim {10}^{-5}$ . This work advances the state of the art in waveform generation for asymmetric-mass binaries, providing open-source tools for the investigation of I/EMRI astrophysics and data analysis. 

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2. Accurate waveforms for eccentric, aligned-spin binary black holes: The multipolar effective-one-body model seobnrv5ehm

   https://doi.org/10.1103/jxrc-z298  

   Gamboa, Aldo; Buonanno, Alessandra; Enficiaud, Raffi; Khalil, Mohammed; Ramos-Buades, Antoni; Pompili, Lorenzo; Estellés, Héctor; Boyle, Michael; Kidder, Lawrence E; Pfeiffer, Harald P; et al (August 2025, Physical Review D)

   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 v5: 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 $20–200M_{\odot }$ 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 v4 and the state-of-the-art esumalí eccentric model. In the quasi-circular-orbit limit, v5 is in excellent agreement with the highly accurate v5 model. The accuracy, robustness, and speed of v5 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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3. Modeling the frequency-domain ringdown amplitude of comparable-mass mergers with greybody factors

   https://doi.org/10.1103/jqgb-mfg1  

   Rosato, Romeo Felice; Yi, Sophia; Berti, Emanuele; Pani, Paolo (March 2026, Physical Review D)

   It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the postmerger ringdown signal. In this work, we demonstrate that a simple four-parameter model based on the greybody factor accurately reproduces the frequency-domain amplitude of a large set of comparable-mass, aligned-spin numerical relativity waveforms from the SXS catalog, achieving mismatches of order $\mathcal{O}\left({10}^{-5}\right)$ and improving existing models by roughly 2 orders of magnitude. We also identify the optimal initial frequency for applying the model in the frequency domain and provide analytical fits of the model parameters in terms of the progenitor masses and aligned spins. Our results pave the way for new consistency tests of the ringdown phase, complementary to traditional black hole spectroscopy. 

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4. Search for eccentric NSBH and BNS mergers in the third observing run of Advanced LIGO and Virgo

   https://doi.org/10.1103/PhysRevD.111.103018  

   Dhurkunde, Rahul; Nitz, Alexander H (May 2025, Physical Review D)

   The possible formation histories of neutron star binaries remain unresolved by current gravitational-wave catalogs. The detection of an eccentric binary system could be vital in constraining compact binary formation models. We present the first search for aligned spin eccentric neutron star-black hole binaries (NSBH) and the most sensitive search for aligned-spin eccentric binary neutron star (BNS) systems using data from the third observing run of the advanced LIGO and advanced Virgo detectors. No new statistically significant candidates are found; we constrain the local merger rate for specific astrophysical models to be less than $150{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ for binary neutron stars in the field, and, 50, 100, and $70{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ for neutron star-black hole binaries in globular clusters, hierarchical triples and nuclear clusters, respectively, at the 90% confidence level if we assume that no sources have been observed from these populations. We predict the capabilities of upcoming and next-generation observatory networks; we investigate the ability of three LIGO ( ${\mathrm{A}}^{\#}$ ) detectors and Cosmic Explorer $\mathrm{CE}\left(20\mathrm{km}\right)+\mathrm{CE}\left(40\mathrm{km}\right)$ to use eccentric binary observations for determining the formation history of neutron star binaries. We find that 2–100 years of observation with three ${\mathrm{A}}^{\#}$ observatories are required before we observe clearly eccentric NSBH binaries; this reduces to only 10 days–1 year with the CE detector network. CE will observe tens to hundreds of measurably eccentric binaries from each of the formation models we consider. 

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5. Sequence modeling of higher-order wave modes of quasi-circular, spinning, non-precessing binary black hole mergers

   https://doi.org/10.1088/1361-6382/ae2bd6  

   Tiki, Victoria; Pham, Kiet; Huerta, E A (December 2025, Classical and Quantum Gravity)

   Abstract Higher-order gravitational wave modes from quasi-circular, spinning, non-precessing binary-black-hole (BBH) mergers encode rich information about the nonlinear dynamics of strong-field gravity. We present a transformer-based sequence-completion surrogate that, given an early-inspiral segment, forecasts the subsequent late inspiral, merger, and ringdown. The intended applications are (i) patching or completing expensive or interrupted numerical-relativity (NR) simulations and (ii) providing late-time cross-checks and rapid hybridization studies. The training set is built from theNRHybSur3dq8surrogate, which provides spherical-harmonic modes up to $\ell \text{⩽}4$ (excluding (4, 0) and $(4,\pm 1)$ , and including (5, 5)) for mass ratios $q\text{⩽}8$ , dimensionless spin components $s_{1,2}^z\in [-0.8,0.8]$ , and inclination angles $\theta \in [0,\pi ]$ . Waveforms are supplied on the interval $t\in [-5000\mathrm{M},-100\mathrm{M})$ and the model autoregressively generates the plus and cross polarizations $(h_{+},h_{\times })$ on $t\in [-100\mathrm{M},130\mathrm{M}]$ . Training on the Delta supercomputer with 16 NVIDIA A100 GPUs required $\sim 15$  h on more than 14 million hybrid waveforms. Evaluation on a held-out test set of $\mathrm{840,000}$ samples yields mean and median overlaps of 0.996 and 0.997, respectively, with respect to the surrogate ground truth. The model generalises reasonably well to out-of-distribution NR simulations from the SXS catalogue: across 521 NR waveforms with mass ratios up toq = 15 and spin magnitudes $|s|\text{⩽}0.998$ , we obtain a median overlap of 0.969, rising to 0.998 for face-on/off orientations. Within the surrogate’s training domain, the transformer provides accurate, millisecond-scale sequence completion of BBH waveforms, including higher-order modes, from early inspiral to ringdown. The NR tests indicate promising performance on higher-fidelity, out-of-distribution data, particularly for detector-favourable orientations. 

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