LISA, the Laser Interferometer Space Antenna, due to launch mid-2035, is a large class space mission by the European Space Agency (ESA). In partnership with NASA and ESA-member states, ESA is on track to launch what is expected to be the first space-based gravitational wave detector. By hosting detectors in space, one gains access to a lower frequency band of gravitational wave sources and, with them, a plethora of new science. To maximise this scientific gain, ESA and NASA selected 20 scientists for the LISA Science Team to carry out and/or lead the necessary actions leading up to LISA's launch. We give a short overview and update of the LISA mission, its science objectives and related waveforms, as well as the work of the LISA Science Team as of April 2026.

The increasing scope and breadth of gravitational wave detectors is providing the opportunity to explore new parameters in gravitational-wave astronomy. Eccentricity and spin-precession are two key observables to infer the origin of a gravitational wave (GW) source. The interpretation of GW source parameters can be plagued by degeneracy, such as the well-known degeneracy between mass and spin. As the field has explored new parameters, questions have been raised about possible degeneracies between eccentricity and spin-precession. Although some state-of-the-art models now include these effects individually, models that incorporate spin-precession and eccentricity are only in their infancy. Until models faithfully cover the complete parameter space of compact binary coalescence, our ability to correctly measure the source parameters and infer the formation of the binary is compromised. Here, we present a study of the distinguishability of these two key parameters. Our work finds that there is indeed a degeneracy between eccentricity and spin-precession; however, it is a highly localized effect. We find that the misidentified eccentricity estimates get worse as the signal gets shorter. Additionally, this misidentification is highly sensitive to the inclination angle of the source system. We provide quantifiable estimates of the potency of this degeneracy in addition to identifying some of the regions of parameter space where this degeneracy exists.

In the past few decades, the waveform community has made advances in producing waveforms that span the inspiral-merger-ringdown of comparable-mass-ratio black hole binaries using advances in post-Newtonian and numerical relativity (NR) theory along with state-of-the-art gravitational wave models. Current methods in NR have shown progress towards producing stable simulations reaching mass ratios of 1:100; however, the computational cost becomes prohibitively expensive as the mass ratio and the length of the simulation increases. Meanwhile, the gravitational self-force (GSF) community has developed waveform models that not only generate extreme mass ratio inspiral waveforms, but also generate near-equal-mass-ratio waveforms with high fidelity. To assess the limits of both the GSF and NR waveforms and alleviate the computational costs of NR, we present hybridized GSF-NR waveforms for non-spinning binary black hole systems in which GSF provides the inspiral, and NR the merger and ringdown. The hybrid waveforms are generated from a set of 68 non-spinning NR waveforms from the SXS catalogue with mass ratios spanning 1:1 to 1:20 and include the (2,2), (2,1), (3,3), (3,2), (4,4), (4,3), and (5,5) spin-weighted spherical harmonic modes. In this paper, we will highlight a selection of these hybrid waveforms and examine the error in the hybridization procedure. We will investigate the impact of subdominant modes on the accuracy of the hybrid waveforms by performing mismatch comparisons with surrogate models. To address the feasibility of hybridizing GSF inspirals with short, high-mass ratio NR waveforms, thereby alleviating computational costs, we will discuss the relationship between mass ratio and the placement of the matching window, which can be used to predict the necessary and optimal number of NR cycles that contribute to the hybrid waveform.

The gravitational-wave event GW231123_135430 is the heaviest binary black hole system observed by the LIGO-Virgo-KAGRA Collaboration to date, with the initial analysis indicating the individual black hole masses lie within or above the theorized pair-instability mass gap of roughly 60 - 130M circle dot. The inference further suggests that both black holes possess high spins, measured to be 0.90 & thorn;0.10-0.19 and 0.80 & thorn;0.20 Therefore, the observation of this event suggests the formation of black holes from channels beyond the standard stellar collapse. However, different waveform models yield significantly different parameter estimates, possibly due to missing physics in the models used in inference. In this work, we carry out a reanalysis of GW231123 using a physically complete model, accounting for both spin precession and eccentricity. Our analysis shows that this event does not exhibit strong evidence for eccentricity, and the exclusion of eccentricity has minimal impact on inference. Furthermore, for GW231123-like systems, even eccentricities as large as 0.15 at 10 Hz do not yield a confident nonzero eccentricity measurement. Through a zero-noise injection recovery study, we show that the observed discrepancies in the parameter estimates can be explained by disagreement in the waveform models at strong spin precession, with the degree of parameter bias in the zero-noise runs being comparable to that observed for the real signal. We also show that inference performed with an eccentric, aligned-spin waveform model can yield a confident nonzero eccentricity measurement due to the degeneracy between eccentricity and spin precession. Bayesian model selection, however, rules out this interpretation in favor of the eccentric, spin precessing hypothesis, which supports zero eccentricity-a conclusion we confirm with additional zero-noise injection-recovery tests.

GW200105_162426 is the first neutron star-black hole merger to be confidently confirmed through either gravitational-wave or electromagnetic observations. Although initially analyzed after detection, the event has recently gained renewed attention following a study [Morras et al. arXiv:2503.15393] that employed a post-Newtonian inspiral-only waveform model and reported strong evidence for orbital eccentricity. In this work, we perform a detailed analysis of GW200105 using state-of-the-art effective-onebody waveform models. Importantly, we present the first study of this event utilizing a physically complete model that incorporates both orbital eccentricity and spin precession across the full inspiral, merger, and ringdown stages, along with higher-order gravitational wave modes. Our results support the presence of eccentricity in the signal, with zero eccentricity excluded from the 99% credible interval, but yielding a mass ratio closer to the original LIGO-Virgo-KAGRA analysis, differing from the findings of [Morras et al. arXiv:2503.15393]. Additionally, similar to a previous eccentric-only analysis [de Lluc Planas et al. Astrophys. J. 995, 47 (2025).], we observe a multimodal structure in the eccentricity posterior distribution. We conduct targeted investigations to understand the origin of this multimodality and complement our analysis with numerical relativity simulations to examine how the inclusion of eccentricity impacts the merger dynamics.

We present a comprehensive assessment of multiparameter tests of general relativity (GR) in the inspiral regime of compact binary coalescences using principal component analysis (PCA). Our analysis is based on an extensive set of simulated gravitational-wave (GW) signals, including both general relativistic and non-GR sources, injected into zero-noise data colored by the noise power spectral densities of the LIGO and Virgo GW detectors at their designed sensitivities. We evaluate the performance of PCA-based methods in the context of two established frameworks: and . For GR-consistent signals, we find that PCA enables stringent constraints on potential deviations from GR, even in the presence of multiple free parameters. Applying the method to simulated signals that explicitly violate GR, we demonstrate that PCA is effective at identifying such deviations. We further test the method using numerical relativity waveforms of eccentric binary black hole systems and show that missing physical effects—such as orbital eccentricity—can lead to apparent violations of GR if not properly included in the waveform models used for analysis. Finally, we apply our PCA-based test to selected real gravitational-wave events from GWTC-3, including GW190814 and GW190412. We present joint constraints from selected binary black hole events in GWTC-3, finding that the 90% credible bound on the most informative PCA parameter is 0.03 − 0.08 + 0.08 in the framework and − 0.0 1 − 0.04 + 0.05 in the framework, both of which are consistent with GR. These results highlight the sensitivity and robustness of the PCA-based approach and demonstrate its readiness for application to future observational data from the fourth observing runs of LIGO, Virgo, and KAGRA.

The Laser Interferometer Space Antenna (LISA) is designed to detect a variety of gravitational-wave events, including mergers of massive black hole binaries, stellar-mass black hole inspirals, and extreme mass-ratio inspirals. LISA's capability to observe signals with high signal-to-noise ratios raises concerns about waveform accuracy. Additionally, its ability to observe long-duration signals will raise the computational cost of Bayesian inference, making it challenging to use costly and novel models with standard stochastic sampling methods without incorporating likelihood and waveform acceleration techniques. In this work, we present our attempt to tackle these issues. We adapt RIFT for LISA to take advantage of its embarrassingly parallel architecture, enabling efficient analysis of large datasets with costly gravitational wave models without relying on likelihood or waveform acceleration. We demonstrate that our open-source code can accurately infer parameters of massive black hole binary signals by carrying out a zero-noise injection recovery using the numerical relativity surrogate model NRHybSur3dq8. By utilizing all available m not equal 0 modes in the inference, we study the impact of higher modes on LISA data analysis. We study the impact of multiple massive black hole binary signals in a dataset on the inference of a single signal, showing that the selected source's inference remains largely unaffected. Furthermore, we analyze the LDC-1A and blind LDC-2A datasets from the Radler and Sangria challenge of the LISA data challenges. When eschewing specialized hardware, we find NRHybSur3dq8 injection-recovery takes approximately 20 h to complete, while the analysis of Sangria and Radler datasets takes about 10 h to complete.

Numerical relativity waveforms are a critical resource in the quest to deepen our understanding of the dynamics of, and gravitational waves emitted from, merging binary systems. We present 181 new numerical relativity simulations as the second MAYA catalog of binary black hole waveforms (a sequel to the Georgia Tech waveform catalog). Most importantly, these include 55 high mass ratio (q >= 4), 48 precessing, and 92 eccentric (e > 0.01) simulations, including 7 simulations which are both eccentric and precessing. With these significant additions, this new catalog fills in considerable gaps in existing public numerical relativity waveform catalogs. The waveforms presented in this catalog are shown to be convergent and are consistent with current gravitational wave models. They are available to the public at https://cgp.ph.utexas.edu/waveform.

As gravitational wave detectors improve in sensitivity, signal-to-noise ratios of compact binary coalescences will dramatically increase, reaching values in the hundreds and potentially thousands. Such strong signals offer both exciting scientific opportunities and pose formidable challenges to the template waveforms used for interpretation. Current waveform models are informed by calibrating or fitting to numerical relativity waveforms and such strong signals may unveil computational errors in generating these waveforms. In this paper, we isolate a single source of computational error, that of the finite grid resolution, and investigate its impact on parameter estimation for aLIGO and Cosmic Explorer. We demonstrate that increasing the inclination angle or decreasing the mass ratio q (q <= 1) raises the resolution required for unbiased parameter estimation. We quantify the error associated with the highest-resolution waveform utilized in our study using an extrapolation procedure on the median of recovered posteriors and confirm the accuracy of current waveforms for the synthetic sources. We introduce a measure to predict the necessary numerical resolution for unbiased parameter estimation and use it to predict that current waveforms are suitable for equal and moderately unequal mass binaries for both detectors. However, current waveforms fail to meet accuracy requirements for high signal-to-noise ratio signals from highly unequal mass ratio binaries (q less than or similar to 1/6), for all inclinations in Cosmic Explorer, and for high inclinations in future updates to LIGO. Given that the resolution requirement becomes more stringent with more unequal mass ratios, current waveforms may lack the necessary accuracy, even at median signal-to-noise ratios for future detectors.

The Laser Interferometer Space Antenna (LISA) is the first scientific endeavour to detect and study gravitational waves from space. LISA will survey the sky for Gravitational Waves in the 0.1 mHz to 1 Hz frequency band which will enable the study of a vast number of objects ranging from Galactic binaries and stellar mass black holes in the Milky Way, to distant massive black-hole mergers and the expansion of the Universe. This definition study report, or Red Book, presents a summary of the very large body of work that has been undertaken on the LISA mission over the LISA definition phase.

In vacuum, the gravitational recoil of the final black hole from the merger of two black holes depends exclusively on the mass ratio and spins of the coalescing black holes, and on the eccentricity of the binary. If matter is present, accretion by the merging black holes may modify significantly their masses and spins, altering both the dynamics of the binary and the gravitational recoil of the remnant black hole. This paper considers such scenario. We investigate the effects on the kick of the final black hole from immersing the binary in a scalar field cloud. We consider two types of configurations: one with non-spinning and unequal-mass black holes, and a second with equal mass and spinning holes. For both types, we investigate how the gravitational recoil of the final black hole changes as we vary the energy density of the scalar field. We find that the accretion of scalar field by the merging black holes could have a profound effect. For the non-spinning, unequal-mass binary black holes, the kicks are in general larger than in the vacuum case, with speeds of approximately 1,200 km/s for binaries with mass ratio 2:1, one order of magnitude larger than in vacuum. For equal mass, binaries with black holes with spins aligned with the orbital angular momentum, kicks larger than in vacuum are also found. For systems with spins in the super-kick configuration, the scalar field triggers a similar dependence of the kicks with the entrance angle at merger as in the vacuum case but in this case depending on the strength of the scalar field.

This report summarizes the envisioned research activities as gathered from the Snowmass 2021 CF5 working group concerning Dark Energy and Cosmic Acceleration: Cosmic Dawn and Before. The scientific goals are to study inflation and to search for new physics through precision measurements of relic radiation from the early universe. The envisioned research activities for this decade (2025-35) are constructing and operating major facilities and developing critical enabling capabilities. The major facilities for this decade are the CMB-S4 project, a new Stage-V spectroscopic survey facility, and existing gravitational wave observatories. Enabling capabilities include aligning and investing in theory, computation and model building, and investing in new technologies needed for early universe studies in the following decade (2035+).

Future detectors such as the Laser Interferometer Space Antenna promise signal-to-noise ratios potentially in the thousands and data containing simultaneous signals. Accurate numerical relativity waveforms will be essential to maximizing the science return. A question of interest to the broad gravitational wave community is: Are the numerical relativity codes ready to face this challenge? Towards answering this question, we provide a new criteria to identify the minimum resolution a simulation must have as a function of signal-to-noise ratio in order for the numerical relativity waveform to be indistinguishable from a true signal. This criteria can be applied to any finite-differencing numerical relativity code with multiple simulations of differing resolutions for the desired binary parameters and waveform length. We apply this criteria to binary systems of interest with the fourth-order MAYA code to obtain the first estimate of the minimum resolution a simulation must have to be prepared for next generation detectors.

The merger of a binary black hole gives birth to a highly distorted final black hole. The gravitational radiation emitted as this black hole relaxes presents us with the unique opportunity to probe extreme gravity and its connection with the dynamics of the black hole horizon. Using numerical relativity simulations, we demonstrate a connection between a concrete observable feature in the gravitational waves and geometrical features on the dynamical apparent horizon of the final black hole. Specifically, we show how the line-of-sight passage of a "cusp"-like defect on the horizon of the final black hole correlates with "chirp"-like frequency peaks in the post-merger gravitational-waves. These post-merger chirps should be observed and analyzed as the sensitivity of LIGO and Virgo increases and as future generation detectors, such as LISA and the Einstein Telescope, become operational.

Gravitational wave (GW) measurements provide the most robust constraints of the mass of astrophysical black holes. Using state-of-the-art GW signal models and a unique parameter estimation technique, we infer the source parameters of the loudest marginal trigger, GW170502, found by LIGO from 2015 to 2017. If this trigger is assumed to be a binary black hole merger, we find it corresponds to a total mass in the source frame of 157(-41)(+55) M-circle dot at redshift z = 1.37(-0.64)(0.93). The primary and secondary black hole masses are constrained to 94(-28)(+44) M-circle dot and 62(-25)(+30) M-circle dot, respectively, with 90% confidence. Across all signal models, we find greater than or similar to 70% probability for the effective spin parameter chi(eff) > 0.1. Furthermore, we find that the inclusion of higher-order modes in the analysis narrows the confidence region for the primary black hole mass by 10%; however, the evidence for these modes in the data remains negligible. The techniques outlined in this study could lead to robust inference of the physical parameters for all intermediate-mass black hole binary candidates (greater than or similar to 100M(circle dot)) in the current GW network.

The NASA LISA Study Team was tasked to study how NASA might support US scientists to participate and maximize the science return from the Laser Interferometer Space Antenna (LISA) mission. LISA is gravitational wave observatory led by ESA with NASA as a junior partner, and is scheduled to launch in 2034. Among our findings: LISA science productivity is greatly enhanced by a full-featured US science center and an open access data model. As other major missions have demonstrated, a science center acts as both a locus and an amplifier of research innovation, data analysis, user support, user training and user interaction. In its most basic function, a US Science Center could facilitate entry into LISA science by hosting a Data Processing Center and a portal for the US community to access LISA data products. However, an enhanced LISA Science Center could: support one of the parallel independent processing pipelines required for data product validation; stimulate the high level of research on data analysis that LISA demands; support users unfamiliar with a novel observatory; facilitate astrophysics and fundamental research; provide an interface into the subtleties of the instrument to validate extraordinary discoveries; train new users; and expand the research community through guest investigator, postdoc and student programs. Establishing a US LISA Science Center well before launch can have a beneficial impact on the participation of the broader astronomical community by providing training, hosting topical workshops, disseminating mock catalogs, software pipelines, and documentation. Past experience indicates that successful science centers are established several years before launch; this early adoption model may be especially relevant for a pioneering mission like LISA.

We are proposing Gravitational-wave Lunar Observatory for Cosmology (GLOC) [1] – a first of its kind fundamental physics experiment on the surface of the Moon. The experiment would access gravitational-waves (GWs) in the frequency range of deci-Hz to 5 Hz, a challenging regime for all Earthbased detectors and space missions. We find that such a lunar-based experiment can survey & 70% of the observable volume of our universe without significant background contamination. This unprecedented sensitivity makes GLOC a powerful cosmic probe for Dark Energy, Dark Matter and physics beyond the Standard Model. In particular, it will independently trace the Hubble expansion rate up to redshift z ∼ 3, provide the strongest limits on the sub-solar Dark Matter candidates and test ΛCDM cosmology up to z ∼ 100. Furthermore, it will have a unique access to GWs from Type Ia supernovae, thus aiding calibration of the standard candles.

A popular approach in numerical simulations of black hole binaries is to model black holes as punctures in the fabric of spacetime. The location and the properties of the black hole punctures are tracked with apparent horizons, namely outermost marginally outer trapped surfaces (MOTSs). As the holes approach each other, a common apparent horizon suddenly appears, engulfing the two black holes and signaling the merger. The evolution of common apparent horizons and their connection with gravitational wave emission have been studied in detail with the framework of dynamical horizons. We present a study of the dynamics of the MOTSs and their punctures in the interior of the final black hole. The study focuses on head-on mergers for various initial separations and mass ratios. We find that MOTSs intersect for most of the parameter space. We show that for those situations in which they do not, it is because of the singularity avoidance property of the moving puncture gauge condition used in the study. Although we are unable to carry out evolutions that last long enough to show the ultimate fate of the punctures, our results suggest that MOTSs always intersect and that at late times their overlap is only partial. As a consequence, the punctures inside the MOTSs, although close enough to each other to act effectively as a single puncture, do not merge.

The first terrestrial gravitational wave interferometers have dramatically underscored the scientific value of observing the Universe through an entirely different window, and of folding this new channel of information with traditional astronomical data for a multimessenger view. The Laser Interferometer Space Antenna (LISA) will broaden the reach of gravitational wave astronomy by conducting the first survey of the millihertz gravitational wave sky, detecting tens of thousands of individual astrophysical sources ranging from white-dwarf binaries in our own galaxy to mergers of massive black holes at redshifts extending beyond the epoch of reionization. These observations will inform - and transform - our understanding of the end state of stellar evolution, massive black hole birth, and the co-evolution of galaxies and black holes through cosmic time. LISA also has the potential to detect gravitational wave emission from elusive astrophysical sources such as intermediate-mass black holes as well as exotic cosmological sources such as inflationary fields and cosmic string cusps.

The direct measurement of gravitational waves is a powerful tool for surveying the population of black holes across the universe. While LIGO has detected black holes as heavy as ~50 M⊙ (ref. 1), there is not yet unambiguous evidence of black holes in the intermediate mass range of 102–5 M⊙. Recent electromagnetic observations have hinted towards the existence of intermediate-mass black holes (IMBHs)2–4; however, their masses remain poorly constrained. Here we argue that multiband observations by space- and ground-based gravitational wave detectors5,6 will be able to survey a broad population of IMBHs at cosmological distances. By utilizing general relativistic simulations of merging black holes7 and state-of-the-art gravitational waveform models8, we classify three distinct populations of binaries with IMBHs and discuss what can be observed about each. Multiband observations involving the upgraded LIGO detector9 and the proposed space-mission LISA10 would detect the inspiral, merger and ring-down of IMBH binaries out to redshift ≈ 2, pushing out to redshift ≈ 5 if next-generation ground-based detectors11,12 are operational at the same time. To facilitate studies of multiband IMBH sources, we provide analytic relations for the maximum redshift of multiband detectability, as a function of black hole mass, for various detector combinations. Our study paves the way for future work on what can be learned from IMBH observations in the era of multiband gravitational wave astronomy. Multi-frequency observations by the upgraded LIGO/Virgo and the proposed LISA space gravitational wave detector will be used to detect intermediate-mass black hole binaries in their inspiral, merger and ring-down phases out to cosmological distances.