arXiv subjects

Geraint Pratten

Publications and source records attributed to Geraint Pratten.

At least 19 recordsLinked to original sources

arXiv2026

Prospects for characterizing Population III remnants with next-generation gravitational-wave observatories

The most distant gravitational-wave (GW) detection by LIGO, Virgo and KAGRA so far is a binary black hole (BBH) merger at a redshift of $z\sim 1.1$, corresponding to a luminosity distance of $D_L \sim 8 \, \rm Gpc$. The next-generation GW detectors, the Einstein Telescope (ET) and Cosmic Explorer (CE), will detect mergers beyond the peak of star formation at $z_{\rm peak}\sim 2$, enabling the direct detection of the remnants of the first stars in the early Universe. Realising this science potential requires accurate inference of the redshift, sky localization and intrinsic properties of the most distant mergers. In this work, using a fully Bayesian framework and an astrophysically motivated model, we study Population III remnants with an ET-CE detector network and quantify the measurement uncertainties in redshift, sky localisation, intrinsic masses and spins for BBHs at $z \geq 15$. Considering an optimistic ($5\, \rm Hz$) and pessimistic ($10\,\rm Hz$) lower cutoff frequency for the detectors' sensitivity, we show that the $5\, \rm Hz$ configuration consistently improves the redshift inference for spin-precessing binaries. We also find that the source-frame component masses can be measured to within $\sim 12\%$ on average, and that the highest-redshift sources in the population can be reliably characterised. In contrast, we find only modest constraints on the BH spins. The improved low-frequency sensitivity also extends the redshift reach of the detector network, enabling events injected at $z_{\rm true}\simeq19.8$ to be confidently identified as originating beyond $z\simeq18.5$ at $90\%$ credibility, compared to a maximum lower-bound redshift of $z\simeq17.5$ for the $10\,\rm Hz$ configuration. Improved detector sensitivity below $10\, \rm Hz$ also reduces the sky-localisation uncertainties, which are essential for cosmological cross-correlation.

astro-ph.HE↗

arXiv2026

High-Post-Newtonian-Order Dynamics Induced by Tail-of-Tail Interactions: The Non-Geodesic Terms

We compute the tail-of-tail contribution to the conservative dynamics of eccentric, non-spinning compact binaries to relative 1PN order and to $\mathcal O(e_t^{12})$. Using the $1$PN quasi-Keplerian dynamics in harmonic coordinates, we derive the Delaunay-averaged Hamiltonian at $5.5$PN and $6.5$PN order and match it to the effective-one-body description, allowing us to determine the corresponding contributions to the non-geodesic EOB $Q$ potential through the $\mathcal{O}(p_r^{12})$, including the dependence on the symmetric mass ratio up to $\mathcal{O}(\nu^2)$. The terms linear in the mass ratio reproduce the available first-order self-force results, while the quadratic terms provide qualitatively new eccentric second-order self-force predictions arising from the tail-of-tail terms. We independently rederive the averaged Hamiltonian using a Fourier--Bessel decomposition of the hereditary interaction. Applying the first law at fixed orbital frequencies, we recover the known first-order self-force redshift through $\mathcal O(e^{12})$ and obtain the complete tail-of-tail contribution to the second-order inverse redshift at $5.5$PN and $6.5$PN through $\mathcal O(e^{10})$.

gr-qc↗

arXiv2026

Binary black hole scattering with generic spins

In this Letter, we confront high-order post-Minkowskian (PM) predictions for generic-spin black-hole scattering with numerical-relativity (NR) simulations for the first time, targeting improvements for eccentric and precessing waveform modelling. We extract azimuthal and polar scattering angles from NR and relate them to the PM spin-kick observable. We introduce asymptotic Euler angles for unbound motion and derive their geometric relation to the scattering angles. Notably, NR exposes a strong-field precessional turning-point structure, including a polar-angle sign change absent in the perturbative PM results.

gr-qc↗

arXiv2026

Fast neural network surrogate for multimodal effective-one-body gravitational waveforms from generically precessing compact binaries

Gravitational waveform templates are a key ingredient for the detection and characterization of gravitational waves emitted by compact binary mergers in the universe. These templates must be physically accurate and extensive, but also highly computationally efficient, two requirements that are often in tension. One solution to this problem is the development of surrogate models, which are fast, data-driven models trained to predict the output of a slower, physically realistic waveform model. In this article we build on existing work to incorporate machine learning techniques into the conventional reduced order surrogate framework, with a focus on extending coverage to waveform models that describe generically precessing quasicircular binaries. In particular, we present SEOBNRv5PHM_NNSur7dq10, a reduced order neural network surrogate of the SEOBNRv5PHM waveform model, valid up to mass ratios 1:10 for precessing quasicircular binary black hole systems with arbitrary spin magnitudes and orientations. The faithfulness of the surrogate to SEOBNRv5PHM is validated, and the surrogate is successfully applied to Bayesian parameter inference using both real and injected gravitational wave data. The surrogate is approximately 5 times faster than SEOBNRv5PHM when evaluating a single waveform on a CPU, and nearly 1000 times faster per-waveform when amortizing the cost over large waveform batches on a GPU.

gr-qc↗

arXiv2026

Post-Newtonian inspiral waveform model for eccentric precessing binaries with higher-order modes and matter effects

We introduce pyEFPEHM, a post-Newtonian (PN) inspiral waveform model for eccentric and spin-precessing compact binaries that includes higher-order modes and matter effects. Accurate and efficient waveform models capturing these effects are essential for probing compact-binary formation channels and exploiting current and future gravitational-wave (GW) observations. pyEFPEHM extends pyEFPE, significantly improving its physical content and accuracy. In particular, we show that above 2.5PN order the quasi-circular contributions to the orbital phasing dominate at each PN order, and incorporate all available higher-order quasi-circular PN corrections to the phasing, including adiabatic tidal effects. We generalize the multiple-scale analysis solution of the spin-precession equations, extending it to higher PN orders and including all available quasi-circular corrections. Finally, we add eccentric corrections up to 1PN order in the waveform amplitudes, including the GW multipoles $(l,|m|)=(2,2),(2,1),(2,0),(3,3),(3,2),(3,1),(3,0),(4,4),(4,2),(4,0)$. We validate pyEFPEHM against analytical waveform models and numerical relativity simulations, showing that it provides a robust and computationally efficient description of the inspiral, with good agreement across a broad region of parameter space and up to close to merger. The accuracy degrades in the late inspiral for systems with very unequal masses ($m_2/m_1 \lesssim 0.1$), significant spins aligned with the orbital angular momentum ($|\chi_\mathrm{eff}| \gtrsim 0.5$), and high eccentricities ($e \gtrsim 0.6$), where the PN expansion is expected to break down. pyEFPEHM represents a significant step toward physically complete and efficient waveform modeling of eccentric and precessing binaries, providing a foundation for future extensions including higher-order corrections, calibration to numerical relativity, and merger ringdown modeling.

gr-qc↗

arXiv2026

LISA science ground segment conventions

This document sets out the conventions used for data simulations, waveforms, and analysis pipelines within the Distributed Data Processing Centre (DDPC) of the Laser Interferometer Space Antenna (LISA). It can also be considered a best practice guide for all publications related to the LISA mission. Topics covered include time-to-frequency transformations, gravitational-wave source parametrization, the instrumental response to gravitational waves, time-delay interferometry, and reference frame definitions.

astro-ph.IM↗

arXiv2026

Impact of eccentricity on the population properties of neutron star - black hole mergers

We revisit the population properties of neutron star-black hole (NSBH) mergers using low-mass compact binary coalescences reported through GWTC-4. Employing pyEFPE, an inspiral-only waveform model that captures both orbital eccentricity and spin-induced precession, we reanalyse all binary neutron star (BNS) and NSBH events observed via gravitational waves. The BNS systems GW170817 and GW190425 are fully consistent with quasi-circular inspirals, while GW200105 stands out among the NSBH binaries as the only system exhibiting significant residual eccentricity at 20 Hz, strengthening evidence for dynamically driven formation pathways. The remaining NSBH events show no measurable eccentricity and appear broadly compatible with low-spin binaries formed through isolated stellar evolution. Using hierarchical Bayesian inference, we obtain the first joint constraints on the mass, spin, and eccentricity distributions of NSBH binaries. Our results also yield the first simultaneous constraints on spin precession and orbital eccentricity in NSBH mergers, while the inferred merger rates remain fully consistent with previous LVK measurements. Treating all NSBH systems as a single population yields results compatible with formation in hierarchical triples, whereas the quasi-circular population remains broadly consistent with isolated evolution. Our results highlight the emerging role of eccentricity as a key discriminator between formation channels. As the number of NSBH detections grows, joint constraints on masses, spins, and orbital eccentricity will enable increasingly sharp tests of dynamical versus isolated binary evolution, establishing NSBH systems as powerful probes of compact-object astrophysics.

astro-ph.HE↗

arXiv2026

Extending Ground-Based Gravitational-Wave Sensitivity to 5 Hz

Extending the sensitivity of terrestrial gravitational-wave detectors below 20 Hz is a long-standing challenge, limited by ground motion and inertial sensing noise. In this letter, we demonstrate ultra-high-vacuum compatible inertial isolation and position sensing technologies that achieve active platform stabilization down to 10 mHz. Our laser position sensors reach a sub-pm/$\sqrt{\rm Hz}$ sensitivity above 10 mHz, independent of the input light polarization, representing a 100-fold improvement over the current LIGO position sensors. In addition, our inertial sensors provide at least a factor of 5 improvement in low-frequency sensitivity compared to state-of-the-art commercial seismometers. We integrate these technologies into a LIGO-like interferometer model and predict a low-frequency sensitivity improvement of up to an order of magnitude at 10 Hz, with enhanced linearity and calibration stability. This extension increases the detection horizon for intermediate-mass black hole binaries of mass $10^3 M_\odot$ by a factor of 3. Our results provide the first experimental demonstration of a practical pathway to sub-10 Hz operation of terrestrial gravitational-wave detectors and establish key technologies for next-generation observatories such as Cosmic Explorer and Einstein Telescope.

astro-ph.IM↗

arXiv2025

Detection of GW200105 with a targeted eccentric search

The neutron star -- black hole (NSBH) binary GW200105 was recently found to have significant residual orbital eccentricity at a gravitational-wave frequency of 20 Hz~\cite{Morras:2025xfu}. The event was originally identified with moderate significance by matched-filter searches that employ non-eccentric templates. The neglect of relevant physical effects, such as orbital eccentricity, can severely reduce the sensitivity of the search and, consequently, also the significance of an event candidate. Here, we present a targeted eccentric search for GW200105. The eccentric search identifies GW200105 as the most significant event with a signal-to-noise ratio of $13.4$ and a false alarm rate of less than 1 in 1000 years. The best-matching template parameters are consistent with the Bayesian inference result, supporting the interpretation of GW200105 as an NSBH that formed through dynamical mechanisms including hierarchical triples and not via isolated binary evolution.

gr-qc↗

arXiv2025

Strong Field Scattering of Two Black Holes: Exploring Gauge Flexibility

Recent advances in post-Minkowskian (PM) gravity provide new avenues for the high precision modeling of compact binaries. In conjunction with the effective one body (EOB) formalism, highly accurate PM informed models of binary black holes on scattering trajectories have emerged. Several complementary approaches currently exist, in particular the SEOB-PM model, the $w$_{\rm EOB} framework and the recent Lagrange-EOB (LEOB) approach. These models incorporate PM results in fundamentally different ways, employing distinct resummation schemes and gauge choices. Notably, both SEOB-PM and LEOB have been used to compute gravitational waves of bound systems, showing excellent agreement with numerical relativity (NR). The essential component to all of the models is the EOB mass-shell condition describing the dynamics of the two-body spacetime. In this work we will investigate how this mass-shell condition is constructed, paying particular attention to the impact of gauge choices and how they interact with different resummation schemes, showing that there is a strong dependence on both coordinate choice and EOB gauge. For the region of parameter space considered, we find that the best performing gauges coincide with the choices made in SEOB-PM and $w$_{\rm EOB}, with other choices exhibiting worse performance. The case of spinning black holes is also considered, where the current techniques for spinning EOB-PM are reviewed and compared. We also introduce a new gauge based upon the centrifugal radius, which improves upon previous models, particularly for large and negative spins. This offers a promising avenue for further resummation of spin information within the EOB-PM framework.

gr-qc↗

arXiv2025

Improved parametrized test of general relativity using the IMRPhenomX waveform family: Including higher harmonics and precession

When testing general relativity (GR) with gravitational wave observations, parametrized tests of deviations from the expected strong-field source dynamics are one of the most widely used techniques. We present an updated version of the parametrized framework with the state-of-art IMRPhenomX waveform family. Our new framework incorporates deviations in the dominant mode as well as in the higher-order modes of the waveform. We demonstrate that the missing physics of either higher-order modes or precession in the parametrized model can lead to a biased conclusion of false deviation from GR. Our new implementation mitigates this issue and enables us to perform the tests for highly asymmetric and precessing binaries without being subject to systematic biases due to missing physics. Finally, we apply the improved test to analyze events observed during the second half of the third observing run of LIGO and Virgo (O3b). We provide constraints on GR deviations by combining O3b results with those from previous observation runs. Our findings show no evidence for violations of GR.

gr-qc↗

arXiv2025

Orbital eccentricity in a neutron star - black hole merger

The observation of gravitational waves from merging black holes and neutron stars provides a unique opportunity to discern information about their astrophysical environment. Two signatures that are considered powerful tracers to distinguish between different binary formation channels are general-relativistic spin-induced orbital precession and orbital eccentricity. Both effects leave characteristic imprints in the gravitational-wave signal that can be extracted from observations. To date, neither precession nor eccentricity have been confidently discerned in merging neutron star - black hole binaries. Here we report the measurement of orbital eccentricity in a neutron star - black hole merger. Using, for the first time, a waveform model that incorporates precession and eccentricity, we perform Bayesian inference on the gravitational-wave event GW200105 (R. Abbott et al. 2021a) and infer a median orbital eccentricity of $e_{20}\sim 0.145$ at an orbital period of 0.1s, ruling out eccentricities smaller than 0.028 with 99.5% confidence. We find inconclusive evidence for the presence of precession, consistent with previous, non-eccentric results, but a more unequal mass ratio. Our result implies a fraction of these binaries will exhibit orbital eccentricity even at small separations, suggesting formation through mechanisms involving dynamical interactions beyond isolated binary evolution. Future observations will reveal the contribution of eccentric neutron star - black hole binaries to the total merger rate across cosmic time.

astro-ph.HE↗

arXiv2025

Improved post-Newtonian waveform model for inspiralling precessing-eccentric compact binaries

The measurement of spin-precession and orbital eccentricity in gravitational-wave (GW) signals is a key priority in GW astronomy, as these effects not only provide insights into the astrophysical formation and evolution of compact binaries but also, if neglected, could introduce significant biases in parameter estimation, searches, and tests of General Relativity. Despite the growing potential of upcoming LIGO-Virgo-KAGRA observing runs and future detectors to measure eccentric-precessing signals, accurately and efficiently modeling them remains a challenge. In this work, we present pyEFPE, a frequency-domain post-Newtonian (PN) waveform model for the inspiral of precessing-eccentric compact binaries. pyEFPE improves upon previous models by introducing analytical expressions for the Fourier mode amplitudes, enhancing the numerical stability of the multiple scale analysis framework, and adding recently derived PN corrections, critical to accurately describe signals in GW detectors. Additionally, we simplify the numerical implementation and introduce a scheme to interpolate the amplitudes, achieving a speedup of up to ~O(15) in the waveform computations, making the model practical for data analysis applications. We thoroughly validate pyEFPE by comparing it to other waveform models in the quasi-circular and eccentric-spin-aligned limits, finding good agreement. Additionally, we demonstrate pyEFPE's capability to analyze simulated GW events, accurately recovering the parameters of signals described by both pyEFPE and IMRPhenomXP. While pyEFPE still lacks important physical effects, such as higher-order PN corrections, higher-order modes, mode asymmetries, tidal interactions or the merger-ringdown phase, it represents a significant step towards more complete waveform models, offering a flexible and efficient framework that can be extended in future work to incorporate these effects.

gr-qc↗

arXiv2024

A geometric template bank for the detection of spinning low-mass compact binaries with moderate orbital eccentricity

Compact binaries on eccentric orbits are another class of gravitational-wave (GW) sources that can provide a wealth of information on binary formation pathways and astrophysical environments. However, historically, eccentricity is often neglected in modelled GW searches for compact binaries. We show that currently used modelled searches that employ quasi-circular template banks are highly ineffectual in detecting binary neutron star (BNS) and neutron star--black hole (NSBH) systems with orbital eccentricities in the range of $[10^{-5},0.15]$ at a GW frequency of $15$Hz. For populations of moderately eccentric BNS and NSBH binaries with (anti-)aligned component spins, we demonstrate that quasi-circular template banks fail to detect up to $\sim 40\%$ of such systems. To alleviate these inefficiencies, we develop the first \emph{geometric} template bank for the search of BNSs and NSBH binaries that includes masses, (anti-)aligned spins and moderate eccentricity. Utilising the post-Newtonian inspiral waveform {\tt TaylorF2Ecc} and a global coordinate transformation, we construct a globally flat metric to efficiently place eccentric templates. Our geometric template bank is highly effectual, and significantly improves the recovery of eccentric signals with less than $6\%$ of signals missed due to the finite template spacing in the bank.

gr-qc↗

arXiv2024

Strong Field Scattering of Black Holes: Assessing Resummation Strategies

Recent developments in post-Minkowksian (PM) calculations have led to a fast-growing body of weak-field perturbative information. As such, there is major interest within the gravitational wave community as to how this information can be used to improve the accuracy of theoretical waveform models. In this work, we build on recent efforts to validate high-order PM calculations using numerical relativity simulations. We present a new set of high-energy scattering simulations for equal-mass, non-spinning binary black holes, further expanding the existing suite of NR simulations. We outline the basic features of three recently proposed resummation schemes (the $\mathscr{L}$-resummed model, the $w^\mathrm{eob}$ model and the SEOB-PM model) and compare the analytical predictions to our NR data. Each model is shown to demonstrate pathological behaviour at high energies, with common features such as PM hierarchical shifts and divergences. The NR data can also be used to calibrate pseudo-5PM corrections to the scattering angle or EOB radial potentials. In each case, we argue that including higher-order information improves the agreement between the analytical models and NR, though the extent of improvement depends on how this information is incorporated and the choice of analytical baseline. Finally, we demonstrate that further resummation of the EOB radial potentials could be an effective strategy to improving the model agreement.

gr-qc↗

arXiv2024

Premerger observation and characterization of massive black hole binaries

We demonstrate an end-to-end technique for observing and characterizing massive black hole binary signals before they merge with the LISA space-based gravitational-wave observatory. Our method uses a zero-latency whitening filter, originally designed for rapidly observing compact binary mergers in ground-based observatories, to be able to observe signals with no additional latency due to filter length. We show that with minimal computational cost, we are able to reliably observe signals as early as 14 days premerger as long as the signal has accrued a signal-to-noise ratio of at least 8 in the LISA data. We also demonstrate that this method can be used to characterize the source properties, providing early estimates of the source's merger time, chirp mass, and sky localization. Early observation and characterization of massive black holes is crucial to enable the possibility of rapid multimessenger observations, and to ensure that LISA can enter a protected operating period when the merger signal arrives.

hep-ex↗

arXiv2024

Stars or gas? Constraining the hardening processes of massive black-hole binaries with LISA

Massive black-hole binaries will be the loudest sources detectable by LISA. These systems are predicted to form during the hierarchical assembly of cosmic structures and coalesce by interacting with the surrounding environment. The hardening phase of their orbit is driven by either stars or gas and encodes distinctive features into the binary black holes that can potentially be reconstructed with gravitational-wave observations. We present a Bayesian framework to assess the likelihood of massive mergers being hardened by either gaseous or stellar interactions. We use state-of-the-art astrophysical models tracking the cosmological evolution of massive black-hole binaries and construct a large number of simulated catalogs of sources detectable by LISA. From these, we select a representative catalog and run both parameter estimation assuming a realistic LISA response as well model comparison capturing selection effects. Our results suggest that, at least within the context of the adopted models, future LISA observations can confidently constrain whether stars or gas are responsible for the binary hardening. We stress that accurate astrophysical modeling of the black-hole spins and the inclusion of subdominant emission modes in the adopted signal might be crucial to avoid systematic biases.

astro-ph.HE↗

arXiv2024

What is the nature of GW230529? An exploration of the gravitational lensing hypothesis

On the 29th of May 2023, the LIGO-Virgo-KAGRA Collaboration observed a compact binary coalescence event consistent with a neutron star-black hole merger, though the heavier object of mass 2.5-4.5 $M_\odot$ would fall into the purported lower mass gap. An alternative explanation for apparent observations of events in this mass range has been suggested as strongly gravitationally lensed binary neutron stars. In this scenario, magnification would lead to the source appearing closer and heavier than it really is. Here, we investigate the chances and possible consequences for the GW230529 event to be gravitationally lensed. We find this would require high magnifications and we obtain low rates for observing such an event, with a relative fraction of lensed versus unlensed observed events of $2 \times 10^{-3}$ at most. When comparing the lensed and unlensed hypotheses accounting for the latest rates and population model, we find a 1/58 chance of lensing, disfavoring this option. Moreover, when the magnification is assumed to be strong enough to bring the mass of the heavier binary component below the standard limits on neutron star masses, we find high probability for the lighter object to have a sub-solar mass, making the binary even more exotic than a mass-gap neutron star-black hole system. Even when the secondary is not sub-solar, its tidal deformability would likely be measurable, which is not the case for GW230529. Finally, we do not find evidence for extra lensing signatures such as the arrival of additional lensed images, type-II image dephasing, or microlensing. Therefore, we conclude it is unlikely for GW230529 to be a strongly gravitationally lensed binary neutron star signal.

gr-qc↗