arXiv subjects

Tessa Baker

Publications and source records attributed to Tessa Baker.

At least 19 recordsLinked to original sources

arXiv2026

No parametrisation, No Problem: A Weakly Modelled Framework to Constrain the Luminosity Distance--Redshift Relation Using Gravitational Wave Sirens

Cosmological tests of general relativity (GR) using gravitational waves (GWs) often rely on parametrised forms of the luminosity distance-redshift ($ d_{\rm L} - z$) relation, which is modified in alternative theories of gravity where the gravitational coupling strength is time-dependent. Although they can lead to stringent results, these parametrisations encapsulate a restricted range of behaviours that may not represent the full variety of modified gravity theories. We present a quasi-model-independent framework to reconstruct deviations from GR in the ratio of the GW to standard electromagnetic luminosity distance. We find that our method can confidently constrain monotonic, irregular, and oscillatory features in the ratio, without biasing population distribution parameters. Applying our framework to GWTC-5 data, we find no deviations from GR. We report that O5-like GW data will not resolve deviations from GR smaller than 30% with our method; however, third generation GW detectors can confidently detect deviations of order 5% to 3$\sigma$ significance.

gr-qc↗

arXiv2026

Rolling Galileons: Evolving Braiding Strength for Viable Dark Energy

Motivated by growing observational indications that dark energy may be dynamical, we introduce Rolling Galileon gravity: a minimal shift-symmetry-breaking extension of the cubic Galileon in which the coupling coefficients are allowed to vary, giving rise to an evolving braiding strength. The full theory space, shown to be closed under field redefinitions, is characterised by two functions. We derive analytical conditions to satisfy three phenomenological requirements: i) a phantom-crossing equation of state at late times, ii) a positive integrated Sachs-Wolfe signature, and iii) absence of pathologies in the screened scalar force in cosmic voids. We show that these conditions are collectively satisfied by an increasing braiding strength relative to the kinetic sector. A Bayesian analysis of minimal Rolling Galileon models finds that they can satisfy the viability requirements i)-iii) whilst providing an acceptable fit to expansion-history data.

astro-ph.CO↗

arXiv2026

Cosmology from Synergies Between SKAO Surveys and Gravitational Wave Observations

Both radio surveys and gravitational wave observations have the potential to probe unprecedented volumes in the Universe with systematics independent of existing cosmological probes. This gives them the potential, especially in combination, to solve some of the outstanding issues in cosmology. Here we show how the use of radio observations as electromagnetic signals tracing large scale structures can be used to provide information on gravitational wave \textit{standard sirens}. By providing a way to link luminosity distance to redshift, this combination can constrain the expansion history of the Universe, and provide information on the Hubble constant ($H_0$). We describe the utility of SKA-Mid neutral hydrogen (\hi) intensity maps, \hi\ galaxy redshift surveys, and continuum galaxy surveys compared to and in conjunction with large contemporaneous optical surveys. Such radio tracers provide a unique, large volume and high redshift information for gravitational wave source, capable of probing effectively the expansion history of the Universe $H(z)$.

astro-ph.CO↗

arXiv2026

Constraints on Horndeski Gravity with Phantom Crossing

Gravity models in which the dark energy equation of state crosses $w=-1$, also known as the phantom divide, have received extensive interest due to recent analyses favouring this behaviour. We introduce a new subclass of Horndeski scalar-tensor models capable of generating phantom crossing, whilst remaining minimally coupled to matter: the Asymptotic Cubic Galileon (ACG) models. We show that ACG models can jointly fit the expansion history inferred from observations of the Planck cosmic microwave background, baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument, and distance-ladder supernovae measurements from the Dark Energy Survey. We then demonstrate that perturbative observables, including the galaxy-ISW cross-correlation and void force profile, provide powerful constraints that confine viable and testable ACG models to a well-defined region of the broader Horndeski landscape. Model comparison metrics, including $\chi^{2}$ and Bayesian evidence, favour both ACG and $w_{0}w_{a}$CDM models over $\Lambda$CDM, with ACG providing a fit of comparable quality to $w_{0}w_{a}$CDM. Crucially, ACG models ground the observationally preferred $w_{0}w_{a}$CDM behaviour in a robust Lagrangian formulation. This enables interpretation beyond mere phenomenological fits, and motivates further tests of these models on nonlinear scales.

astro-ph.CO↗

arXiv2026

Radio sirens: inferring $H_0$ with binary black holes and neutral hydrogen in the era of the Einstein Telescope and the SKA Observatory

A new synergy between gravitational waves (GWs) and the study of the large-scale structure of the Universe is now emerging. Along this line of research, we combine simulated observations of stellar-origin black hole mergers and neutral hydrogen 21 cm line intensity mapping to probe the expansion rate of the Universe through the distance-redshift relation. GW signals from binary black holes provide direct distance information, while neutral hydrogen intensity maps offer a tomographic view of the large-scale structure of the Universe. Using the 3-dimensional density fields of hydrogen as a redshift prior for GW events, we explore a novel dark-sirens-like approach, here termed radio sirens, to measure the late-time expansion history of the Universe. We study the performance of the next-generation GW observatories, such as the Einstein Telescope, to ensure enough statistics and access to high-redshift data. On the other hand, future spectroscopic intensity mapping surveys with the SKA-Mid telescope are expected to trace the underlying dark matter distribution at large scales up to redshift $z\sim 3$. This combined methodology allows us to constrain the Hubble constant to $\sim 8\%$ precision, using around 3,000 GW events with signal-to-noise ratios greater than 150. This corresponds to an improvement of around $90\%$ compared to not considering the information from the neutral hydrogen maps.

astro-ph.CO↗

arXiv2026

A Master Equation for Screening in Luminal Horndeski Gravity

Determining the active screening mechanism from a general scalar-tensor Lagrangian remains a challenging problem. As a diagnostic tool, we present a systematic study of nonlinear cosmological perturbations in luminal Horndeski theories. Working in the $\alpha$-basis on a flat FLRW background, we derive and organise the full set of unapproximated second-order perturbation equations and systematically apply the quasistatic and weak-field limits. We find that second-order effects modify only the scalar-field equation. We derive, for static and spherically symmetric configurations, a master screening equation that classifies the nonlinear operators driving screening, recovering the Vainshtein mechanism and the onset of chameleon screening. We also identify a novel candidate regime, which we term Phaedrus screening, characterised by a screening radius that scales linearly with the source mass. For each mechanism, we derive analytical and numerical solutions and clarify the conditions under which they activate. Two new publicly available software packages are introduced: (i) xAlpha, a Mathematica package to compute and organize perturbation equations in scalar-tensor theories, and (ii) escut, a python module to solve the nonlinear scalar equation. In many cases, these tools enable the identification of the active screening type directly from a luminal Horndeski Lagrangian.

gr-qc↗

arXiv2026

Illuminating the Physics of Cosmic Origin and Evolution: A UK Space Frontiers 2035 White Paper

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5~$\mu$m wavelength coverage at moderate resolution, allowing precise redshift measurements in the $1<z<4$ range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

astro-ph.IM↗

arXiv2026

Probing Cosmic Expansion and Early Universe with Einstein Telescope

Over the next two decades, gravitational-wave (GW) observations are expected to evolve from a discovery-driven endeavour into a precision tool for astrophysics, cosmology, and fundamental physics. Current second-generation ground-based detectors have established the existence of compact-binary mergers and enabled GW multi-messenger astronomy, but they remain limited in sensitivity, redshift reach, frequency coverage, and duty cycle. These limitations prevent them from addressing many fundamental open questions in cosmology. By the 2040s, wide-field electromagnetic surveys will have mapped the luminous Universe with unprecedented depth and accuracy. Nevertheless, key problems including the nature of dark matter, the physical origin of cosmic acceleration, the properties of gravity on cosmological scales, and the physical conditions of the earliest moments after the Big Bang will remain only partially constrained by electromagnetic observations alone. Progress on these fronts requires access to physical processes and epochs that do not emit light. Gravitational waves provide a unique and complementary observational channel: they propagate over cosmological distances largely unaffected by intervening matter, probe extreme astrophysical environments, and respond directly to the geometry of spacetime. In this context, next-generation GW observatories such as the Einstein Telescope (ET) will be transformative for European astronomy. Operating at sensitivities and frequencies beyond existing detectors, ET will observe binary black holes and neutron stars out to previously inaccessible redshifts, enable continuous high signal-to-noise monitoring of compact sources, and detect gravitational-wave backgrounds of astrophysical and cosmological origin. Together with space-based detectors, ET will play a central role in advancing our understanding of cosmic evolution and fundamental physics.

astro-ph.CO↗

arXiv2025

Illuminating the Dark Sector: Understanding Modified Gravity Signatures with Cross-Correlations of Gravitational Waves and Large-Scale Structure

We investigate the synergy between large-scale structure (LSS) observations and gravitational wave (GW) events for testing modified gravity. In particular, we forecast the LSS $\times$ GW cross-correlation signal using Stage-IV LSS surveys, such as Euclid, in combination with future detections from the Einstein Telescope. This cross-correlation provides a novel probe of fundamental physics, potentially revealing deviations from the $\Lambda$CDM paradigm that may not be accessible through electromagnetic observations alone. We describe the considered modified gravity scenarios, the relevant LSS and GW observables, and the synthetic forecast methodology. Our results demonstrate that combining LSS and GWs can significantly enhance constraints on departures from General Relativity, opening a new window for multi-messenger cosmology. We further assess the observational requirements GW experiments must meet to improve upon constraints obtainable from LSS alone.

astro-ph.CO↗

arXiv2025

First measurement of the Hubble constant from gravitational wave-galaxy cross-correlations

We measure for the first time the Hubble constant ($H_0$) from the cross-correlation of galaxies and gravitational waves (GW), by applying the $\textit{Peak Sirens}$ method. This method consists of finding the peak of the 3D angular cross-spectrum $C_{\ell}(z,D_L)$ between the galaxy redshifts ($z$) and the GW luminosity distances ($D_L$). Using two GW events from the GWTC-3.0 catalog and the GLADE+ galaxy catalog, we make the first detection of the cross-correlation peak at $5.9\sigma$ confidence. This signal comes mostly from the best localized event in the catalog, GW190814, which alone provides a $3.4\sigma$ significance. Adding also the multimessenger event GW170817, but without using its known redshift, we find $H_0 = 67^{+18}_{-15}$ km s$^{-1}$Mpc$^{-1}$ and the first observational constraint on the GW bias, $b_{\rm gw} < 4.3$ at 95\% CI. These measurements set the stage for future novel cosmological constraints with this technique.

astro-ph.CO↗

arXiv2025

Multi-messenger lensing time delay as a probe of the graviton mass

Gravitational lensing is a powerful probe of cosmology and astrophysics. With the prospect of the first strongly lensed gravitational waves on the horizon, we highlight an opportunity to test fundamental physics. In this work, we assume a nonzero mass for the graviton, which leads to gravitational waves following timelike geodesics instead of null geodesics. We derive standard gravitational lensing equations, such as the scattering angle, the time-delay between different images and the magnification, which normally rely on the assumption of null geodesics. We show that a single strongly lensed multi-messenger event is enough to constrain the graviton mass to $m< 3 \cdot 10^{-23}$ eV/c$^{2}$. Notably this constraint is independent of the lens model, the waveform model, and of cosmology. Additionally, we explore magnification of images and find that they offer at least three orders of magnitude weaker bounds than the time delay, and have a dependence on the correct modeling of the lens and cosmology.

gr-qc↗

arXiv2025

Cosmic Cartography II: completing galaxy catalogs for gravitational-wave cosmology

The dark siren method exploits the complementarity between gravitational-wave binary coalescence signals and galaxy catalogs originating from the same regions of space. However, all galaxy catalogs are incomplete, i.e. they only include a subset of all galaxies, typically being biased towards the bright end of the luminosity distribution. This sub-selection systematically affects the dark siren inference of the Hubble constant $H_0$, so a completeness relation has to be introduced that accounts for the missing objects. In the literature it is standard to assume that the missing galaxies are uniformly distributed across the sky and that the galaxy magnitude distribution is known. In this work we develop a novel method which improves upon these assumptions and reconstructs the underlying true galaxy field, respecting the spatial correlation of galaxies on large scales. In our method the true magnitude distribution of galaxies is inferred alongside the spatial galaxy distribution. Our method results in an improved three-dimensional prior in redshift and sky position for the host galaxy of a GW event, which is expected to make the resulting $H_0$ posterior more robust. Building on our previous work, we make a number of improvements, and validate our method on simulated data based on the Millennium simulation. The inference results can be reproduced through our publicly available code base light.

astro-ph.CO↗

arXiv2025

Exploring future synergies for large-scale structure between gravitational waves and radio sources

Future third-generation gravitational wave detectors like the Einstein Telescope (ET) and Cosmic Explorer (CE) are expected to detect millions of binary black hole (BBH) mergers. Alongside these advances, upcoming radio surveys, such as the Square Kilometer Array Observatory (SKAO) will provide new sets of cosmological tracers. These include mapping the large-scale distribution of neutral hydrogen (\hi) using intensity mapping (IM) and \hi\ and radio continuum galaxies. In this work, we will investigate synergies between gravitational waves (GW) and radio tracers through a multi-tracer approach. We first forecast the precision on the clustering bias of GWs by cross-correlating data from an ET-like detector with an SKAO IM survey. Our results indicate that this approach can constrain the GW clustering bias to within $2\%$ up to $z = 2.5$. Additionally, we explore the potential of a triple cross-correlation using GWs, IM, and photometric galaxies from a survey like the Vera Rubin Observatory's Legacy Survey of Space and Time (LSST). This multi-tracer method enhances constraints on the magnification lensing effect, achieving percent-level precision, and allows for a measurement of the Doppler effect with approximately $15\%$ uncertainty. Furthermore we show for the first time that this method could achieve the precision required to measure subdominant gravitational potential contributions to the relativistic corrections, which had thought to be below cosmic variance. Our analysis highlights the potential of cross-correlations between GWs and radio tracers to improve constraints on astrophysical properties of BBHs, measure relativistic effects, and perform null tests of GR in cosmological scales.

astro-ph.CO↗

arXiv2025

Multi-messenger Gravitational Lensing

We introduce the rapidly emerging field of multi-messenger gravitational lensing - the discovery and science of gravitationally lensed phenomena in the distant universe through the combination of multiple messengers. This is framed by gravitational lensing phenomenology that has grown since the first discoveries in the 20th century, messengers that span 30 orders of magnitude in energy from high energy neutrinos to gravitational waves, and powerful "survey facilities" that are capable of continually scanning the sky for transient and variable sources. Within this context, the main focus is on discoveries and science that are feasible in the next 5-10 years with current and imminent technology including the LIGO-Virgo-KAGRA network of gravitational wave detectors, the Vera C. Rubin Observatory, and contemporaneous gamma/X-ray satellites and radio surveys. The scientific impact of even one multi-messenger gravitational lensing discovery will be transformational and reach across fundamental physics, cosmology and astrophysics. We describe these scientific opportunities and the key challenges along the path to achieving them. This article is the introduction to the Theme Issue of the Philosophical Transactions of The Royal Society A on the topic of Multi-messenger Gravitational Lensing, and describes the consensus that emerged at the associated Theo Murphy Discussion Meeting in March 2024.

astro-ph.HE↗

arXiv2025

A Bright Future? Prospects for Cosmological Tests of GR with Multimessenger Gravitational Wave Events

Further bright sirens - gravitational wave events with electromagnetic counterparts - are keenly awaited, but proving elusive. The exceptional event GW170817 had a profound impact on the landscape of viable cosmological extensions of General Relativity (GR); can we expect this kind of shift to be repeated in the next decade? In this work we will assess the potential constraints from bright sirens in the LIGO-Virgo-KAGRA O5 era and third generation detector era. We set up the statistical formalism for our constraints, and generate and analyse simulated data in the context of general scalar-tensor theories. We highlight the important role that gamma-ray burst detection has in breaking key parameter degeneracies. We find that the next ten bright sirens alone will not competitively constrain cosmological gravity, but that one year of third generation observations could confidently detect mild departures from GR, e.g. the Horndeski parameter $\alpha_{\rm M}\neq 0$ is detected at greater than $3\sigma$. This justifies investment in a broad range of methods for gravitational wave cosmology (dark sirens, bright sirens and cross-correlation with large-scale structure) to ensure tests of cosmological gravity advance in both the short-term and the long-term.

gr-qc↗

arXiv2024

Cosmic Cartography: Bayesian reconstruction of the galaxy density informed by large-scale structure

The dark sirens method combines gravitational waves and catalogs of galaxies to constrain the cosmological expansion history, merger rates and mass distributions of compact objects, and the laws of gravity. However, the incompleteness of galaxy catalogs means faint potential host galaxies are unobserved, and must be modeled to avoid inducing a bias. The majority of dark sirens analyses to date assume that the missing galaxies are distributed uniformly across the sky, which is clearly unphysical. We introduce a new Bayesian approach to the reconstruction of galaxy catalogs, which makes full use of our knowledge of large-scale structure. Our method quantifies the uncertainties on the estimated true galaxy number count in each voxel, and is marginalized over cosmological parameters and bias parameters. Crucially, our method further assesses the (absolute) magnitude distribution of galaxies, which is not known from the galaxy catalog itself. We present the details of our method and validate our approach on a galaxy catalog associated to the Millennium Simulation. The tools developed here generate physically-informed and robust host galaxy reconstructions, enabling more informative dark sirens analyses. Stage IV galaxy surveys will display greater redshift overlap with GW observations, whilst remaining incomplete -- emphasizing the importance of our work.

astro-ph.CO↗

arXiv2024

Gravitational waves and galaxies cross-correlations: a forecast on GW biases for future detectors

Gravitational waves (GWs) have rapidly become important cosmological probes since their first detection in 2015. As the number of detected events continues to rise, upcoming instruments like the Einstein Telescope (ET) and Cosmic Explorer (CE) will observe millions of compact binary (CB) mergers. These detections, coupled with galaxy surveys by instruments such as DESI, Euclid, and the Vera Rubin Observatory, will provide unique information on the large-scale structure of the universe by cross-correlating GWs with the distribution of galaxies which host them. In this paper, we focus on how these cross-correlations constrain the clustering bias of GWs emitted by the coalescence of binary black holes (BBH). This parameter links BBHs to the underlying dark matter distribution, hence informing us how they populate galaxies. Using a multi-tracer approach, we forecast the precision of these measurements under different survey combinations. Our results indicate that current GW detectors will have limited precision, with measurement errors as high as $\sim50\%$. However, third-generation detectors like ET, when cross-correlated with LSST data, can improve clustering bias measurements to within $2.5\%$. Furthermore, we demonstrate that these cross-correlations can enable a percent-level measurement of the magnification lensing effect on GWs. Despite this, there is a degeneracy between magnification and evolution biases, which hinders the precision of both. This degeneracy is most effectively addressed by assuming knowledge of one bias or targeting an optimal redshift range of $1 < z < 2.5$. Our analysis opens new avenues for studying the distribution of BBHs and testing the nature of gravity through large-scale structure.

astro-ph.CO↗

arXiv2024

Large scale structure prior knowledge in the dark siren method

Gravitational wave dark sirens are a powerful tool for cosmology and inference of compact object population hyperparameters. They allow for a measurement of the luminosity distance to the source, but not their redshift. Galaxy catalogues in the source localization volume can be used to infer the redshift of the source in a statistical manner. Catalogues are, however, limited by their incompleteness, which can be significant at redshifts corresponding to current GW events. In this work, we detail how to implement in practice variance completion, a novel galaxy completion method which uses knowledge of the large scale structure to optimize the potential of dark sirens analyses. We compress the prediction for the missing number of galaxies into a ratio between the predictions of variance completion and the standard homogeneous completion method. This ratio format can be easily incorporated into existing line of sight computations used in dark sirens software; we demonstrate this procedure using the GLADE+ galaxy catalogue and the gwcosmo software package. We discuss the robustness of the method, and apply it to well-localized event GW190814 as a proof of concept. Finally, we apply the method to data from the third observing run of LIGO-Virgo-KAGRA, finding that it yields results that are consistent with homogeneous completion. We also discuss the prospects for an improvement if the GW localization volume shrinks.

astro-ph.CO↗