arXiv subjects

Anna Heffernan

Publications and source records attributed to Anna Heffernan.

18 recordsLinked to original sources

arXiv2026

LISA and the LISA Science Team

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.

astro-ph.IM↗

arXiv2025

Parameter estimation for the GWTC-4.0 catalog with phenomenological waveform models that include orbital eccentricity and an updated description of spin precession

The GWTC-4.0 catalog of transient gravitational wave signals describes observations made in the first part of the fourth observing run of the LIGO-Virgo-KAGRA (LVK) gravitational wave detector network. Here we extend the LVK's GWTC-4.0 analysis to elliptic orbits, and an improved description of spin precession in the frequency domain. For this study we use state-of-the-art waveforms from the IMRPhenom family (specifically XPNR, TPHM, and TEHM), and we consider the 84 confidently detected events that are consistent with binary-black-hole mergers. We present an extended catalog of updated posterior samples, quantify how incorporation of these waveform effects alters inferred source properties relative to previous analyses, and discuss waveform systematics.

gr-qc↗

arXiv2025

Adiabatic tides in compact binaries on quasi-elliptic orbits: Dynamics at the second-and-a-half relative post-Newtonian order

GW200105 is the first gravitational wave detection to show signs of eccentricity, it also is a neutron star - blackhole binary. This raises the need for waveforms that incorporate tidal effects on quasi-elliptic orbits. We tackle the problem of finite size effects within the post-Newtonian framework, including the mass-type quadrupole and octupole, as well as the current-type quadrupole deformations in the adiabatic approximation. The computations are performed at the second-and-a-half relative post-Newtonian order. We first derive the quasi-Keplerian parametrization of the conservative motion; we then express the radial separation and phase with their time derivatives in terms of the orbital frequency, the time eccentricity and the eccentric anomaly. To obtain these as functions of time, we invert the generalized Kepler equation while also discussing the convergence of eccentricity expanded results. We provide those results to the fourteenth order in eccentricity. Finally, we exploit the already known radiation reaction term of the acceleration in order to derive the secular and oscillatory evolutions of the orbital elements. The companion paper contains the derivation of the radiated fluxes and the amplitude modes of the strain. All relevant results are provided in an ancillary file.

gr-qc↗

arXiv2025

Science of the LISA mission: A Summary for the European Strategy for Particle Physics

The LISA mission is an international collaboration between ESA, its member states, and NASA, for the detection of gravitational waves from space. It was adopted in January 2024 and is scheduled for launch in the mid-2030's. It will be a constellation of three identical spacecraft forming a near-equilateral triangle in an heliocentric orbit, transferring laser beams over $2.5 \cdot 10^6$ km long arms. Laser interferometry is used to track separations between test masses, thus measuring spacetime strain variations as a function of time. LISA Science Objectives tackle many open questions in astrophysics, fundamental physics and cosmology, including ESA's Cosmic Vision questions "What are the fundamental laws of the universe?" and "How did the universe originate and of what is it made?". In this contribution, based on the LISA Red Book, we present a summary of the LISA Science Objectives relevant for the European Strategy for Particle Physics.

gr-qc↗

arXiv2025

PhenomXPNR: An improved gravitational wave model linking precessing inspirals and NR-calibrated merger-ringdown

We present the frequency-domain quasi-circular precessing binary-black-hole model PhenomXPNR. This model combines the most precise available post-Newtonian description of the evolution of the precession dynamics through inspiral with merger-ringdown model informed by numerical relativity. This, along with a phenomenological model of the dominant multipole asymmetries, results in the most accurate and complete representation of the physics of precessing binaries natively in the frequency-domain to date. All state-of-the-art precessing models show bias when inferring binary parameters in certain regions of the parameter space. We demonstrate that the developments presented ensure that for some precessing systems PhenomXPNR shows the least degree of bias. Further, as a phenomenological, frequency-domain model, PhenomXPNR remains one of the most computationally efficient models available and is therefore well-suited to the era of gravitational-wave astronomy with its ever growing rate of detected signals.

gr-qc↗

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↗

arXiv2024

Tests of General Relativity with GW230529: a neutron star merging with a lower mass-gap compact object

On May 29, 2023, the LIGO Livingston observatory detected the gravitational-wave signal GW230529_181500 from the merger of a neutron star with a lower mass-gap compact object. Its long inspiral signal provides a unique opportunity to test general relativity (GR) in a parameter space previously unexplored by strong-field tests. In this work, we performed parameterized inspiral tests of GR with GW230529_181500. Specifically, we search for deviations in the frequency-domain GW phase by allowing for agnostic corrections to the post-Newtonian coefficients. We performed tests with the Flexible Theory Independent and Test Infrastructure For General Relativity frameworks using several quasicircular waveform models that capture different physical effects (higher modes, spins, tides). We find that the signal is consistent with GR for all deviation parameters. Assuming the primary object is a black hole, we obtain particularly tight constraints on the dipole radiation at $-1$PN order of $|\delta\hat{\varphi}_{-2}| \lesssim 8 \times 10^{-5}$, which is a factor $\sim17$ times more stringent than previous bounds from the neutron star--black hole merger GW200115_042309, as well as on the 0.5PN and 1PN deviation parameters. We discuss some challenges that arise when analyzing this signal, namely biases due to correlations with tidal effects and the degeneracy between the 0PN deviation parameter and the chirp mass. To illustrate the importance of GW230529_181500 for tests of GR, we mapped the agnostic $-1$PN results to a class of Einstein-scalar-Gauss-Bonnet (ESGB) theories of gravity. We also conducted an analysis probing the specific phase deviation expected in ESGB theory and obtain an upper bound on the Gauss-Bonnet coupling of $\ell_{\rm GB} \lesssim 0.51~\rm{M}_\odot$ ($\sqrt{\alpha_{\rm GB}} \lesssim 0.28$ km), which is better than any previously reported constraint.

gr-qc↗

arXiv2024

LISA Definition Study Report

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.

astro-ph.CO↗

arXiv2023

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

gr-qc↗

arXiv2022

Self-force regularization of a point particle for generic orbits in Kerr spacetime: electromagnetic and gravitational cases

The self-force is the leading method in modelling waveforms for extreme mass ratio inspirals, a key target of ESA's future space-based gravitational wave detector LISA. In modelling these systems, one approximates the smaller body as a point particle leading to problematic singularities that need to be removed. Modelling of this singular structure has settled on the Detweiler-Whiting singular field as the gold standard. As a solution to the governing wave equation itself, on removal, it leaves a smooth regular field that is a solution to the homogeneous wave equation, much like its well established flat spacetime counterpart. The mode-sum method enables subtraction of this singularity mode by mode via a spherical harmonic decomposition. The more modes one has, the faster the convergence in the $\ell$-sum, making these expressions highly beneficial, especially considering the heavy computational burden of waveform production. Until recently, only the two leading orders were known for generic orbits in Kerr spacetime. In a previous paper, we produced the next non-zero parameter for a scalar charged particle in curved spacetime, laying the groundwork for the electromagnetic and gravitational case which we present here.

gr-qc↗

arXiv2021

Regularization of a scalar charged particle for generic orbits in Kerr spacetime

A scalar charged particle moving in a curved background spacetime will emit a field affecting its own motion; the resolving of this resulting motion is often referred to as the self-force problem. This also serves as a toy model for the astrophysically interesting compact body binaries, extreme mass ratio inspirals, targets for the future space-based gravitational wave detector, LISA. In the modelling of such systems, a point-particle assumption leads to problematic singularities which need to be safely removed to solve for the motion of the particle regardless of the scenario: scalar, electromagnetic or gravitational. Here, we concentrate on a scalar charged particle and calculate the next order of the Detweiler-Whiting singular field and its resulting regularisation parameter when employing the mode-sum method of regularisation. This enables sufficiently faster self-force calculations giving the same level of accuracy with significantly less $\ell$ modes. Due to the similarity of the governing equations, this also lays the groundwork for similar calculations for an electromagnetic or mass charged particle in Kerr spacetime and has applications in other regularisation schemes like the effective source and matched expansion.

gr-qc↗

arXiv2020

Optimisation of non-pharmaceutical measures in COVID-19 growth via neural networks

On 19th March, the World Health Organisation declared a pandemic. Through this global spread, many nations have witnessed exponential growth of confirmed cases brought under control by severe mass quarantine or lockdown measures. However, some have, through a different timeline of actions, prevented this exponential growth. Currently as some continue to tackle growth, others attempt to safely lift restrictions whilst avoiding a resurgence. This study seeks to quantify the impact of government actions in mitigating viral transmission of SARS-CoV-2 by a novel soft computing approach that makes concurrent use of a neural network model, to predict the daily slope increase of cumulative infected, and an optimiser, with a parametrisation of the government restriction time series, to understanding the best set of mitigating actions. Data for two territories, Italy and Taiwan, have been gathered to model government restrictions in traveling, testing and enforcement of social distance measures as well as people connectivity and adherence to government actions. It is found that a larger and earlier testing campaign with tighter entry restrictions benefit both regions, resulting in significantly less confirmed cases. Interestingly, this scenario couples with an earlier but milder implementation of nationwide restrictions for Italy, thus supporting Taiwan's lack of nationwide lockdown. The results, found with a purely data-driven approach, are in line with the main findings of mathematical epidemiological models, proving that the proposed approach has value and that the data alone contains valuable knowledge to inform decision makers.

q-bio.OT↗

arXiv2019

The unique potential of extreme mass-ratio inspirals for gravitational-wave astronomy

The inspiral of a stellar-mass compact object into a massive ($\sim 10^{4}$-$10^{7} M_{\odot}$) black hole produces an intricate gravitational-wave signal. Due to the extreme-mass ratios involved, these systems complete $\sim 10^{4}$-$10^{5}$ orbits, most of them in the strong-field region of the massive black hole, emitting in the frequency range $\sim10^{-4}-1~$Hz. This makes them prime sources for the space-based observatory LISA (Laser Interferometer Space Antenna). LISA observations will enable high-precision measurements of the physical characteristics of these extreme-mass-ratio inspirals (EMRIs): redshifted masses, massive black hole spin and orbital eccentricity can be determined with fractional errors $\sim 10^{-4}$-$10^{-6}$, the luminosity distance with better than $\sim 10\%$ precision, and the sky localization to within a few square degrees. EMRIs will provide valuable information about stellar dynamics in galactic nuclei, as well as precise data about massive black hole populations, including the distribution of masses and spins. They will enable percent-level measurements of the multipolar structure of massive black holes, precisely testing the strong-gravity properties of their spacetimes. EMRIs may also provide cosmographical data regarding the expansion of the Universe if inferred source locations can be correlated with galaxy catalogs.

astro-ph.HE↗

arXiv2017

Accelerated motion and the self-force in Schwarzschild spacetime

We provide expansions of the Detweiler-Whiting singular field for motion along arbitrary, planar accelerated trajectories in Schwarzschild spacetime. We transcribe these results into mode-sum regularization parameters, computing previously unknown terms that increase the convergence rate of the mode-sum. We test our results by computing the self-force along a variety of accelerated trajectories. For non-uniformly accelerated circular orbits we present results from a new 1+1D discontinuous Galerkin time-domain code which employs an effective-source. We also present results for uniformly accelerated circular orbits and accelerated bound eccentric orbits computed within a frequency-domain treatment. Our regularization results will be useful for computing self-consistent self-force inspirals where the particle's worldline is accelerated with respect to the background spacetime.

gr-qc↗

arXiv2016

GTOC8: Results and Methods of ESA Advanced Concepts Team and JAXA-ISAS

We consider the interplanetary trajectory design problem posed by the 8th edition of the Global Trajectory Optimization Competition and present the end-to-end strategy developed by the team ACT-ISAS (a collaboration between the European Space Agency's Advanced Concepts Team and JAXA's Institute of Space and Astronautical Science). The resulting interplanetary trajectory won 1st place in the competition, achieving a final mission value of $J=146.33$ [Mkm]. Several new algorithms were developed in this context but have an interest that go beyond the particular problem considered, thus, they are discussed in some detail. These include the Moon-targeting technique, allowing one to target a Moon encounter from a low Earth orbit; the 1-$k$ and 2-$k$ fly-by targeting techniques, enabling one to design resonant fly-bys while ensuring a targeted future formation plane% is acquired at some point after the manoeuvre ; the distributed low-thrust targeting technique, admitting one to control the spacecraft formation plane at 1,000,000 [km]; and the low-thrust optimization technique, permitting one to enforce the formation plane's orientations as path constraints.

physics.space-ph↗

arXiv2014

The Self-Force Problem: Local Behaviour of the Detweiler-Whiting Singular Field

The growing reality of gravitational wave astronomy is giving age-old problems a new lease of life; one such problem is that of the self-force. A charged or massive particle moving in a curved background space-time produces a field that affects its motion, pushing it off its expected geodesic. This self-field gives rise to a so-called self-force acting on the particle. In modelling this motion, the self-force approach uses a perturbative expansion in the mass ratio. One of the most interesting sources of gravitational waves are extreme mass ratio inspirals - systems perfectly suited to self-force modelling. One of the key problems within the self-force model is the divergence of the field at the particle. To resolve this, the field is split into a singular component and a smooth regular field. This regular-singular split, introduced by Detweiler and Whiting, is used in most modern self-force calculations. In this thesis, we derive high-order expansions of the Detweiler-Whiting singular field, and use these to push the boundaries on current precision limits of self-force calculations. Within the mode-sum scheme, we give over 14 previously unknown regularisation parameters, almost doubling the current regularisation parameter database. We also produce smooth effective sources to high order, and propose an application of the higher terms to improve accuracy in the m-mode scheme. Finally, we investigate the status of the cosmic censorship conjecture and the role that the self-force plays. To this end, we give regularisation parameters for non-geodesic motion. We also show the necessity of our results in the exciting area of second order self-force calculations, which benefit significantly from high-order coordinate expansions of the singular field. We calculate several parameters that these schemes require, and highlight the further advancements possible from the results of this thesis.

gr-qc↗

arXiv2014

High-order expansions of the Detweiler-Whiting singular field in Kerr spacetime

In a previous paper, we computed expressions for the Detweiler-Whiting singular field of point scalar, electromagnetic and gravitational charges following a geodesic of the Schwarzschild spacetime. We now extend this to the case of equatorial orbits in Kerr spacetime, using coordinate and covariant approaches to compute expansions of the singular field in scalar, electromagnetic and gravitational cases. As an application, we give the calculation of previously unknown mode-sum regularization parameters. We also propose a new application of high-order approximations to the singular field, showing how they may be used to compute $m$-mode regularization parameters for use in the $m$-mode effective source approach to self-force calculations.

gr-qc↗

arXiv2013

High-order expansions of the Detweiler-Whiting singular field in Schwarzschild spacetime

The self field of a charged particle has a component that diverges at the particle. We use both coordinate and covariant approaches to compute an expansion of this singular field for generic geodesic orbits in Schwarzschild spacetime for scalar, electromagnetic and graviational cases. We check agreement of both approaches and give, as an application, the calculation of previously unknown regularisation parameters. In this so-called "mode-sum regularization" approach, each mode of the field is finite, while their sum diverges. The sum may be rendered finite and convergent by the subtraction of "regularization parameters". Higher order parameters lead to faster convergence in the mode-sum. As a second example application, we compute high order expressions for the effective source approach to self-force calculations.

gr-qc↗