arXiv subjects

Maxence Corman

Publications and source records attributed to Maxence Corman.

15 recordsLinked to original sources

arXiv2026

Probing ultralight bosons with LISA observations of spinning black hole mergers and follow-up searches of merger remnants

Ultralight bosons can trigger superradiant instabilities around rotating black holes, extracting angular momentum and leading in some cases to observable gravitational signatures. When the associated spin-down timescale is shorter than the black hole lifetimes and the spin-up timescales due to, e.g. accretion, this process imposes an upper limit on black hole spins. In addition, the formation and subsequent dissipation of boson clouds generates quasi-continuous gravitational wave emission. In this work, we explore the prospects for constraining and detecting ultralight bosons with observations of massive black hole binary mergers with the space-based LISA observatory. We consider two complementary approaches: measurements of black hole spins from merging binaries and follow-up gravitational wave searches targeting massive black hole binary merger remnants. We consider three population models for massive black holes, based on either heavy or light seeds, and forecast the exclusion and detection probabilities for both scalar and vector bosons. We find that black hole spin measurements can constrain scalar masses in the range $[5\times10^{-18},10^{-14}]$ eV and vector masses in the range $[6\times10^{-19},2\times10^{-14}]$ eV, with the exact range depending on the model. In contrast, restricting to vector bosons, follow-up gravitational wave searches are sensitive to a narrower vector boson mass range of $\sim[3\times10^{-17},3\times10^{-15}]$ eV, with the specific values again depending on the model. If a vector boson with a mass in the range $[10^{-16},2\times10^{-15}]$ eV existed, the probability of having an event that the follow-up searches would be sensitive to ranges from very small to near unity depending on the astrophysical model.

gr-qc↗

arXiv2026

Binary neutron star mergers with a subsolar mass star

While there are a number of proposed formation channels for subsolar mass compact objects, including black holes formed primordially, or neutron stars that form in collapsar disks, there have yet to be any conclusive observations of such objects. Motivated by the possibility that, if such objects exist, gravitational waves from binary mergers may reveal them, we study binary neutron star mergers where one star has a subsolar-mass in order to determine how well such systems are described by current models, and when they could be distinguished from a system with a subsolar-mass black hole. We perform fully general-relativistic simulations of a $1.7\ M_{\odot}$ star merging with a $0.8\ M_{\odot}$ star, leading to tidal deformabilities of up to $\mathcal{O}(10^4)$ for the latter, and quantify how this affects the merger dynamics and associated gravitation and electromagnetic signals. In this regime, we find mass transfer between the stars, as well as significantly lower disruption frequencies. Though this is not captured by current gravitational waveform models, we conclude that this does not significantly impact the sensitivity of current gravitational wave detectors to these sources. Assuming design sensitivity of the LIGO and Virgo detectors, we find no biases in the recovered intrinsic parameters for signal-to-noise ratios $\lesssim 100$. We also find that the large deformabilities lead to a significant increase in the amount of dynamically ejected matter compared to equal mass systems, exceeding the predictions of current phenomenological models.

astro-ph.HE↗

arXiv2026

Testing gravitational wave polarizations with LISA

In this paper we quantify the ability of the Laser Interferometer Space Antenna (LISA) to test the presence of non-tensorial polarizations as well as modifications to the tensor ones in gravitational waves emitted from massive black hole binaries. We employ the Parametrized Post-Einsteinian (PPE) formalism to model deviations from General Relativity (GR) for tensor, vector, and scalar polarizations. Our PPE parametrization is inspired by post-Newtonian waveforms from four modified gravity theories: Horndeski, Einstein-aether, Rosen's bimetric, and Lightman-Lee. We consistently implement these modifications across the inspiral, merger, and ringdown phases, ensuring proper waveform alignment and tapering. Subsequently, we perform Fisher forecasts to derive expected constraints on deviations from General Relativity and map these constraints to the parameter spaces of the four gravity theories. For tensor polarizations, LISA achieves constraints on amplitude modifications ranging between $\sim 10^{-4}-10^{-2}$ precision level, depending on the frequency evolution of the modifications, for systems with $10^5-10^7 {\, \rm M}_\odot$ at $z = 1$. We find that LISA can distinguish breathing and longitudinal scalar polarizations only for relatively light binaries with $M \lesssim 10^4 {\, \rm M}_\odot$, beyond which these modes become degenerate in the detector response. Importantly, constraints on vector polarizations are approximately 2-3 times more precise than for scalar polarizations. For both vector and scalar modes, amplitude measurements reach precisions ranging between $\sim 10^{-8}-10^{-2}$, depending on the frequency evolution of the modifications, for systems with $10^5-10^7 {\, \rm M}_\odot$ at $z = 1$. These results demonstrate LISA's potential to probe gravity in the strong-field regime via gravitational wave polarizations.

astro-ph.CO↗

arXiv2025

Black hole binaries in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity experience a slower merger phase

In shift-symmetric Einstein-scalar-Gauss-Bonnet gravity, stationary black holes have a non-vanishing scalar charge. During the inspiral, the phase evolution is modified by several effects, primarily an additional scalar dipole radiation, which enters at -1PN order. This effect accelerates the inspiral when compared to general relativity, when including corrections up to 2PN. Using fully non-linear numerical simulations of quasi-circular, comparable mass binaries, we find that in the late stages the orbital dynamics are altered so that the overall effect is instead a decelerated merger phase for the modified gravity case. We attribute this to a change in the conservative dynamics, and show that at the late inspiral stage more energy must be emitted in scalar-Gauss-Bonnet gravity to induce a given change in frequency. In longer signals, this should lead to a distinctive switch between a faster and slower frequency evolution relative to general relativity as the binary approaches merger. This work suggests we should revisit existing constraints on the theory that are obtained assuming PN approximations apply up to merger, or based on order by order approximations that neglect backreaction effects on the metric, and shows the importance of including non-linear effects that modify the gravitational sector in the strong field regime.

gr-qc↗

arXiv2025

Signatures from metastable oppositely-charged black hole binaries in scalar Gauss-Bonnet gravity

We conduct numerical simulations of inspiraling, oppositely-charged black holes in the class of scalar-Gauss-Bonnet theories that exhibit spontaneous black hole scalarization. For quasi-circular, equal-mass binaries near the existence threshold for scalarized solutions, we find a new phenomenon whereby one of the component black holes can suddenly flip the sign of its scalar charge during the inspiral. We confirm this phenomenon with two independent codes and identify two key signatures thereof: a change in the dominant scalar radiation channel (from dipolar to quadrupolar), and, strikingly, the introduction of eccentricity in the orbit. This scenario offers a concrete example of potential nonlinear departures from general relativity in the inspiral of binary black holes in alternative theories of gravity and is of relevance for the development of new tests of gravity.

gr-qc↗

arXiv2025

The SXS Collaboration's third catalog of binary black hole simulations

We present a major update to the Simulating eXtreme Spacetimes (SXS) Collaboration's catalog of binary black hole simulations. Using highly efficient spectral methods implemented in the Spectral Einstein Code (SpEC), we have nearly doubled the total number of binary configurations from 2,018 to 3,756. The catalog now densely covers the parameter space with precessing simulations up to mass ratio $q=8$ and dimensionless spins up to $|\vec{\chi}|\le0.8$ with near-zero eccentricity. The catalog also includes some simulations at higher mass ratios with moderate spin and more than 250 eccentric simulations. We have also deprecated and rerun some simulations from our previous catalog (e.g., simulations run with a much older version of SpEC or that had anomalously high errors in the waveform). The median waveform difference (which is similar to the mismatch) between resolutions over the simulations in the catalog is $4\times10^{-4}$. The simulations have a median of 22 orbits, while the longest simulation has 148 orbits. We have corrected each waveform in the catalog to be in the binary's center-of-mass frame and exhibit gravitational-wave memory. We estimate the total CPU cost of all simulations in the catalog to be 480,000,000 core-hours. We find that using spectral methods for binary black hole simulations is over 1,000 times more efficient than much shorter finite-difference simulations of comparable accuracy. The full catalog is publicly available through the sxs Python package and at https://data.black-holes.org .

gr-qc↗

arXiv2025

The Science of the Einstein Telescope

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

gr-qc↗

arXiv2024

Black hole-neutron star mergers in Einstein-scalar-Gauss-Bonnet gravity

Gravitational wave observations of black hole-neutron star binaries, particularly those where the black hole has a lower mass compared to other observed systems, have the potential to place strong constraints on modifications to general relativity that arise at small curvature length scales. Here we study the dynamics of black hole-neutron star mergers in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity, a representative example of such a theory, by numerically evolving the full equations of motion. We consider quasi-circular binaries with different mass-ratios that are consistent with recent gravitational wave observations, including cases with and without tidal disruption of the star, and quantify the impact of varying the coupling controlling deviations from general relativity on the gravitational wave signal and scalar radiation. We find that the main effect on the late inspiral is the accelerated frequency evolution compared to general relativity, and that--even considering Gauss-Bonnet coupling values approaching those where the theory breaks down--the impact on the merger gravitational wave signal is mild, predominately manifesting as a small change in the amplitude of the ringdown. We compare our results to current post-Newtonian calculations and find consistency throughout the inspiral.

gr-qc↗

arXiv2024

Nonlinear studies of modifications to general relativity: Comparing different approaches

Studying the dynamical, nonlinear regime of modified theories of gravity remains a theoretical challenge that limits our ability to test general relativity. Here we consider two generally applicable, but approximate methods for treating modifications to full general relativity that have been used to study binary black hole mergers and other phenomena in this regime, and compare solutions obtained by them to those from solving the full equations of motion. The first method evolves corrections to general relativity order by order in a perturbative expansion, while the second method introduces extra dynamical fields in such a way that strong hyperbolicity is recovered. We use shift-symmetric Einstein-scalar-Gauss-Bonnet gravity as a benchmark theory to illustrate the differences between these methods for several spacetimes of physical interest. We study the formation of scalar hair about initially non-spinning black holes, the collision of black holes with scalar charge, and the inspiral and merger of binary black holes. By directly comparing predictions, we assess the extent to which those from the approximate treatments can be meaningfully confronted with gravitational wave observations. We find that the order-by-order approach cannot faithfully track the solutions when the corrections to general relativity are non-negligible. The second approach, however, can provide consistent solutions, provided the ad-hoc timescale over which the dynamical fields are driven to their target values is made short compared to the physical timescales.

gr-qc↗

arXiv2022

Starting inflation from inhomogeneous initial conditions with momentum

We investigate the circumstances under which cosmic inflation can arise from very inhomogeneous initial conditions using numerical relativity simulations. Previous studies have not considered cases with non-zero momentum density due to technical challenges with solving the coupled Einstein constraint equations. Here we address these, introducing and comparing several different ways of constructing cosmological initial conditions with inhomogeneous scalar field and time derivative profiles. We evolve such initial conditions with large inhomogeneities in both single- and two-field inflationary models. We study cases where the initial gradient and kinetic energy are much larger than the inflationary energy scale, and black holes can form, as well as cases where the initial scalar potential energy is comparable, as in scenarios where inflation occurs at nearly Planckian densities, finding large-field inflation to be generally robust. We consider examples of initial conditions where a large scalar field velocity towards non-inflationary values would prevent inflation from occurring in the homogeneous case, finding that the addition of large gradients in the scalar field can actually dilute this effect, with the increased expansion and non-vanishing restoring force leading to inflation.

gr-qc↗

arXiv2022

Nonlinear studies of binary black hole mergers in Einstein-scalar-Gauss-Bonnet gravity

We study the nonlinear dynamics of binary black hole systems with scalar charge by numerically evolving the full equations of motion for shift-symmetric Einstein scalar Gauss-Bonnet gravity. We consider quasi-circular binaries with different mass-ratios, varying the Gauss-Bonnet coupling and quantifying its impact on the emitted scalar and gravitational waves. We compare our numerical results to post-Newtonian calculations of the radiation emitted during the inspiral. We demonstrate the accuracy of the leading-order terms in post-Newtonian theory in modeling the amplitude of the scalar waveform, but find that, at least for the last few orbits before merger, the currently available post-Newtonian theory is not sufficient to model the dephasing of the gravitational wave signal in this theory. We further find that there is non-negligible nonlinear enhancement in the scalar field at merger, but that the effect on the peak gravitational wave emission is small.

gr-qc↗

arXiv2022

Evolution of black holes through a nonsingular cosmological bounce

We study the classical dynamics of black holes during a nonsingular cosmological bounce. Taking a simple model of a nonsingular bouncing cosmology driven by the combination of a ghost and ordinary scalar field, we use nonlinear evolutions of the Einstein equations to follow rotating and non-rotating black holes of different sizes through the bounce. The violation of the null energy condition allows for a shrinking black hole event horizon and we find that for sufficiently large black holes (relative to the minimum Hubble radius) the black hole apparent horizon can disappear during the contraction phase. Despite this, we show that most of the local cosmological evolution remains largely unaffected by the presence of the black hole. We find that, independently of the black hole's initial mass, the black hole's event horizon persists throughout the bounce, and the late time dynamics consists of an expanding universe with a black hole of mass comparable to its initial value.

gr-qc↗

arXiv2021

Constraining cosmological extra dimensions with gravitational wave standard sirens: from theory to current and future multi-messenger observations

The propagation of gravitational waves (GWs) at cosmological distances offers a new way to test the gravitational interaction at the largest scales. Many modified theories of gravity, usually introduced to explain the observed acceleration of the universe, can be probed in an alternative and complementary manner with respect to standard electromagnetic (EM) observations. In this paper we consider a homogeneous and isotropic cosmology with extra spatial dimensions at large scales, which represents a simple phenomenological prototype for extra-dimensional modified gravity cosmological models. By assuming that gravity propagates through the higher-dimensional spacetime, while photons are constrained to the usual four dimensions of general relativity, we derive from first principles the relation between the luminosity distance measured by GW detectors and the one inferred by EM observations. We then use this relation to constrain the number of cosmological extra dimensions with the binary neutron star event GW170817 and the binary black hole merger GW190521. We further provide forecasts for the Laser Interferometer Space Antenna (LISA) by simulating multi-messenger observations of massive black hole binary (MBHB) mergers. This paper extends and updates previous analyses which crucially neglected an additional redshift dependency in the GW-EM luminosity distance relation which affects results obtained from multi-messenger GW events at high redshift, in particular constraints expected from LISA MBHBs.

gr-qc↗

arXiv2021

Nonlinear dynamics of flux compactification

We study the nonlinear evolution of unstable flux compactifications, applying numerical relativity techniques to solve the Einstein equations in $D$ dimensions coupled to a $q$-form field and positive cosmological constant. We show that initially homogeneous flux compactifications are unstable to dynamically forming warped compactifications. In some cases, we find that the warping process can serve as a toy-model of slow-roll inflation, while in other instances, we find solutions that eventually evolve to a singular state. Analogous to dynamical black hole horizons, we use the geometric properties of marginally trapped surfaces to characterize the lower dimensional vacua in the inhomogeneous and dynamical settings we consider. We find that lower-dimensional vacua with a lower expansion rate are dynamically favoured, and in some cases find spacetimes that undergo a period of accelerated expansion followed by contraction.

hep-th↗

arXiv2020

Constraining extra dimensions on cosmological scales with LISA future gravitational wave siren data

We investigate the idea that current cosmic acceleration could be the consequence of gravitational leakage into extra dimensions on cosmological scales rather than the result of a non-zero cosmological constant, and consider the ability of future gravitational-wave siren observations to probe this phenomenon and constrain the parameters of phenomenological models of this gravitational leakage. In theories that include additional non-compact spacetime dimensions, the gravitational leakage intro extra dimensions leads to a reduction in the amplitude of observed gravitational waves and thereby a systematic discrepancy between the distance inferred to such sources from GW and EM observations. We investigate the capability of a gravitational space interferometer such as LISA to probe this modified gravity on large scales. We find that the extent to which LISA will be able to place limits on the number of spacetime dimensions and other cosmological parameters characterising modified gravity will strongly depend on the actual number and redshift distribution of sources, together with the uncertainty on the GW measurements. A relatively small number of sources ($\sim 1$) and high measurement uncertainties would strongly restrict the ability of LISA to place meaningful constraints on the parameters in cosmological scenarios where gravity is only five-dimensional and modified at scales larger than about $\sim 4$ times the Hubble radius. Conversely, if the number of sources observed amounts to a four-year average of $\sim 27$, then in the most favourable cosmological scenarios LISA has the potential to place meaningful constraints on the cosmological parameters with a precision of $\sim 1\%$ on the number of dimensions and $\sim 7.5\%$ on the scale beyond which gravity is modified, thereby probing the late expansion of the universe up to a redshift of $\sim 8$.

astro-ph.CO↗