arXiv subjects

Daniele Vernieri

Publications and source records attributed to Daniele Vernieri.

At least 19 recordsLinked to original sources

arXiv2026

Cosmological constraints and standard sirens forecasts for non-dynamical dark energy in Horndeski gravity

We investigate an analytically tractable sector of the Extended Cuscuton model, a non-dynamical dark-energy realization within the framework of viable Horndeski gravity. We focus on four benchmark submodels and constrain them with current background probes, namely cosmic chronometers, Type-Ia supernovae, and BAO, while imposing theoretical viability, Lunar Laser Ranging, and Big Bang Nucleosynthesis bounds. We then forecast third-generation bright-standard-siren constraints with Einstein Telescope and Cosmic Explorer networks, considering prompt-emission, afterglow, and kilonova counterparts. Current data already restrict the viable parameter space to small departures from $Λ$CDM and do not remove the calibration-driven offset between the CC+SN and CC+BAO determinations of $H_0$. In principle, future bright sirens substantially sharpen the constraints, especially for kilonova catalogues and extended detector networks. Across the forecast configurations, the relative uncertainty on $H_0$ remains below $13.18\%$ and can reach $0.21\%$ in the most constraining cases, while $Ω_Λ$ is recovered at the percent level in the best cases. These results show that third-generation standard sirens can provide a precise complementary test of non-dynamical dark energy beyond $Λ$CDM.

astro-ph.CO↗

arXiv2026

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↗

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

Joint estimation of the cosmological model and the mass and redshift distributions of the binary black hole population with the Einstein Telescope

We investigate the capability of constraining the mass and redshift distributions of binary black hole systems jointly with the underlying cosmological model using one year of observations of the Einstein Telescope. To this aim, we fixed the underlying cosmological model to a flat $Λ$CDM model, then we considered the mass distribution given by a smoothed power law, and the redshift distributions given by the Madau-Dickinson model. We built mock catalogs with different SNR thresholds, and finally inferred astrophysical and cosmological parameters jointly adopting a hierarchical Bayesian framework. We found that as the SNR threshold decreases, the precision on the matter density parameter $Ω_{m,0}$ and the Hubble constant $H_0$, improves significantly due to the increased number of detectable events at high redshift. However, degeneracies between cosmological and astrophysical parameters exist and evolve with the SNR threshold. Finally, we showed that one year of observations will serve to reconstruct the mass distribution with its features. Conversely, the redshift distribution will be poorly constrained and will need more observations to improve.

astro-ph.CO↗

arXiv2024

General analysis of Noether symmetries in Horndeski gravity

We explore Noether symmetries of Horndeski gravity, extending the classification of general scalar-tensor theories. Starting from the minimally coupled scalar field and the first-generation scalar-tensor gravity, the discussion is generalised to kinetic gravity braiding and Horndeski gravity. We highlight the main findings by focusing on the non-minimally coupled Gauss-Bonnet term and the extended cuscuton model. Finally, we discuss how the presence of matter can influence Noether symmetries. It turns out that the selected Horndeski functions are unchanged with respect to the vacuum case.

gr-qc↗

arXiv2024

Parity violation in gravitational waves and observational bounds from third-generation detectors

In this paper, we analyze parity-violating effects in the propagation of gravitational waves (GWs). For this purpose, we adopt a newly proposed parametrized post-Einstenian (PPE) formalism, which encodes modified gravity corrections to the phase and amplitude of GW waveforms. In particular, we focus our study on three well-known examples of parity-violating theories, namely Chern-Simons, Symmetric Teleparallel and Hor\v ava-Lishitz gravity. For each model, we identify the PPE parameters emerging from the inclusion of parity-violating terms in the gravitational Lagrangian. Thus, we use the simulated sensitivities of third-generation GW interferometers, such as the Einstein Telescope and Cosmic Explorer, to obtain numerical bounds on the PPE coefficients and the physical parameters of binary systems. In so doing, we find that deviations from General Relativity cannot be excluded within given confidence limits. Moreover, our results show an improvement of one order of magnitude in the relative accuracy of the GW parameters compared to the values inferred from the LIGO-Virgo-KAGRA network. In this respect, the present work demonstrates the power of next-generation GW detectors to probe fundamental physics with unprecedented precision.

gr-qc↗

arXiv2024

Can the NANOGrav observations constrain the geometry of the universe?

The theory of inflation provides an elegant explanation for the nearly flat universe observed today, which represents one of the pillars of the standard cosmological model. However, recent studies have reported some deviations from a flat geometry, arguing that a closed universe would be instead favored by observations. Given its central role played in the cosmological context, this paper revisits the issue of spatial curvature in light of the stochastic gravitational wave background signal recently detected by the NANOGrav collaboration. For this purpose, we investigate the primordial gravitational waves generated during inflation and their propagation in the post-inflationary universe. We propose a new parametrization of the gravitational wave power spectrum, taking into account spatial curvature, the tensor-to-scalar ratio and the spectral index of tensor perturbations. Therefore, we compare the theoretical predictions with NANOGrav data to possibly constrain the geometry of the universe. We find that the choice of the priors has a significant effect on the computed posterior distributions. In particular, using flat uniform priors results in $Ω_{\mathcal{K},0}= 0.00 \pm 0.67$ at the 68\% confidence level. On the other hand, imposing a Planck prior, we obtain $Ω_{\mathcal{K},0}= -0.05 \pm 0.17$ at the 68\% confidence level. This result aligns with the analysis of the cosmic microwave background radiation, and no deviations from a flat universe are found.

astro-ph.CO↗

arXiv2023

Role of spatial curvature in the primordial gravitational wave power spectrum

This paper investigates the effects of nonvanishing spatial curvature on the propagation of primordial gravitational waves produced during inflation. In particular, we consider tensor perturbations over a homogeneous and isotropic background, and describe the propagation of gravitational waves in the de Sitter phase with spatially curved geometries. We thus derive the expression of the primordial power spectrum at the horizon crossing, in the case of open and closed universes. Then, we analyze how tensor modes propagate in the post-inflationary era, showing the evolution of transfer functions in the radiation and matter epochs, as well as the matching conditions in the intermediate regime. To account for the intrinsic nature of different relativistic species, we also explore the corrections to the standard behavior of the radiation energy density. For this purpose, we introduce the effective number of degrees of freedom of relativistic particles contributing to the primordial energy and entropy densities. Under the subhorizon approximation, we obtain the spectral energy density of relic gravitational waves in terms of the curvature density parameter. Finally, we discuss the capability of present and future experiments to detect the primordial gravitational wave signal at different frequency regimes.

astro-ph.CO↗

arXiv2023

Fluid nature constrains Horndeski gravity

The elusive physical nature of Horndeski gravity is elucidated in a new approach depicting this class of theories as a dissipative effective fluid. Requiring the constitutive equations of the latter to be those of a Newtonian fluid restricts the theory to only two disconnected subclasses of "viable" Horndeski gravity. Therefore, a stress-energy tensor of Horndeski effective fluid, linear in the first derivatives of the fluid's 4-velocity, is a sufficient condition for gravitational waves to propagate at light speed. All other Horndeski theories correspond to exotic non-Newtonian effective fluids.

gr-qc↗

arXiv2023

Exploiting the Einstein Telescope to solve the Hubble tension

We probe four cosmological models which, potentially, can solve the Hubble tension according to the dark energy equation of state. In this context, we demonstrate that the Einstein Telescope is capable of achieving a relative accuracy below $1\%$ on the Hubble constant independently of the specific dark energy model. We firstly build mock catalogs containing gravitational wave events for one, five and ten years of observations, and above Signal-to-Noise Ratio equal to nine. From these catalogs, we extract the events which are most likely associated with possible electromagnetic counterpart detected by THESEUS. Finally, we select four dark energy models, namely a non-flat $ω$CDM, an interacting dark energy, an emergent dark energy, and a time varying gravitational constant model, to forecast the precision down to which the Einstein Telescope can bound the corresponding cosmological parameters. We foresee that the Hubble constant is always constrained with less than $1\%$ uncertainty, thereby offering a potential solution to the Hubble tension. The accuracy on the other cosmological parameters is at most comparable with the one currently obtained using multiple probes, except for the emergent dark energy model for which the Einstein Telescope alone will be able to improve the current limits by more than one order of magnitude.

astro-ph.CO↗

arXiv2022

Testing Horndeski gravity with S2 star orbit

We have explored a completely new and alternative way to restrict the parameter space of Horndeski theory of gravity. Using its Newtonian limit, it is possible to test the theory at a regime where, given its complexity and the small magnitude of the expected effects, it is poorly probed. At Newtonian level, it gives rise to a generalized Yukawa-like Newtonian potential which we have tested using S2 star orbit data. Our model adds five parameters to the General Relativity model, and the analysis constrains two of them with unprecedented precision to these energy scales, while only gives an exclusion region for the remaining parameters. We have shown the potential of weak-field tests to constrain Horndeski gravity opening, as a matter of fact, a new avenue that deserves to be further, and deeply, explored near in the future.

gr-qc↗

arXiv2022

Constraining $Λ$CDM cosmological parameters with Einstein Telescope mock data

We investigate the capability of Einstein Telescope to constrain the cosmological parameters of the non-flat $Λ$CDM cosmological model. Two types of mock datasets are considered depending on whether or not a short Gamma-Ray Burst is detected and associated with the gravitational wave emitted by binary neutron stars merger using the THESEUS satellite. Depending on the mock dataset, two statistical estimators are applied: one assumes that the redshift is known, while the other marginalizes over it assuming a specific redshift prior distribution. We demonstrate that {\em (i)} using mock catalogs collecting gravitational wave signals emitted by binary neutron stars systems to which a short Gamma-Ray Burst has been associated, Einstein Telescope may achieve an accuracy on the cosmological parameters of $σ_{H_0}\approx 0.40$ km s$^{-1}$ Mpc$^{-1}$, $σ_{Ω_{k,0}}\approx 0.09$, and $σ_{Ω_{Λ,0}}\approx 0.07$; while {\em (ii)} using mock catalogs collecting all gravitational wave signals emitted by binary neutron stars systems for which an electromagnetic counterpart has not been detected, Einstein Telescope may achieve an accuracy on the cosmological parameters of $σ_{H_0}\approx 0.04$ km s$^{-1}$ Mpc$^{-1}$, $σ_{Ω_{k,0}}\approx 0.01$, and $σ_{Ω_{Λ,0}}\approx 0.01$, once the redshift probability distribution of GW events is known from population synthesis simulations and/or the measure of the tidal deformability parameter. These results show an improvement of a factor 2-75 with respect to earlier results using complementary datasets.

astro-ph.CO↗

arXiv2022

Generalized McVittie geometry in Horndeski gravity with matter

We investigate McVittie and generalized McVittie solutions for Horndeski gravity with a spatially homogeneous gravitational scalar field, which is stealth at small scales near the central object but, at large scales, sources the FLRW universe in which the central inhomogeneity is embedded. Unlike previous studies, we include matter and obtain generalized McVittie solutions in the extended cuscuton model. The possible configurations are classified according to the time-dependence of the gravitational coupling, the radial energy flow, the accretion rate onto the central object, and the Hubble rate.

gr-qc↗

arXiv2022

Bouncing Cosmology in Fourth-Order Gravity

The Big Bang initial singularity problem can be solved by means of bouncing solutions. In the context of extended theories of gravity, we will look for covariant effective actions whose field equations contain up to fourth-order derivatives of the metric tensor. In finding such bouncing solutions, we will make use of an order reduction technique based on a perturbative approach. Reducing the order of the field equations to second-order, we are able to find solutions which are perturbatively close to General Relativity. We will build the covariant effective actions of the resulting order reduced theories.

gr-qc↗

arXiv2021

Effective Actions for Loop Quantum Cosmology in Fourth-Order Gravity

Loop Quantum Cosmology (LQC) is a theory which renders the Big Bang initial singularity into a quantum bounce, by means of short range repulsive quantum effects at the Planck scale. In this work, we are interested in reproducing the effective Friedmann equation of LQC, by considering a generic $f(R,P,Q)$ theory of gravity, where $R=g^{μν}R_{μν}$ is the Ricci scalar, $P=R_{μν}R^{μν}$, and $Q=R_{αβμν}R^{αβμν}$ is the Kretschmann scalar. An order reduction technique allows us to work in $f(R,P,Q)$ theories which are perturbatively close to General Relativity, and to deduce a modified Friedmann equation in the reduced theory. Requiring that the modified Friedmann equation mimics the effective Friedmann equation of LQC, we are able to derive several functional forms of $f(R,P,Q)$. We discuss the necessary conditions to obtain viable bouncing cosmologies for the proposed effective actions of $f(R,P,Q)$ theory of gravity.

gr-qc↗

arXiv2021

Exact Solutions in Higher-Dimensional Lovelock and $AdS_5$ Chern-Simons Gravity

Lovelock gravity in $D$-dimensional space-times is considered adopting Cartan's structure equations. In this context, we find out exact solutions in cosmological and spherically symmetric backgrounds. In the latter case, we also derive horizons and the corresponding Bekenstein--Hawking entropies. Moreover, we focus on the topological Chern--Simons theory, providing exact solutions in 5 dimensions. Specifically, it is possible to show that Anti-de Sitter invariant Chern--Simons gravity can be framed within Lovelock--Zumino gravity in 5 dimensions, for particular choices of Lovelock parameters.

gr-qc↗

arXiv2021

Effective $f(R)$ actions for modified Loop Quantum Cosmologies via order reduction

General Relativity is an extremely successful theory, at least for weak gravitational fields, however, it breaks down at very high energies, such as in correspondence of the initial singularity. Quantum Gravity is expected to provide more physical insights concerning this open question. Indeed, one alternative scenario to the Big Bang, that manages to completely avoid the singularity, is offered by Loop Quantum Cosmology (LQC), which predicts that the Universe undergoes a collapse to an expansion through a bounce. In this work, we use metric $f(R)$ gravity to reproduce the modified Friedmann equations which have been obtained in the context of modified loop quantum cosmologies. To achieve this, we apply an order reduction method to the $f(R)$ field equations, and obtain covariant effective actions that lead to a bounce, for specific models of modified LQC, considering matter as a scalar field.

gr-qc↗

arXiv2020

Non-Local Curvature and Gauss-Bonnet Cosmologies by Noether Symmetries

Non-local gravity cosmologies are considered under the standard of Noether Symmetry Approach. In particular, we focus on non-local theories whose gravitational actions depend on curvature and Gauss-Bonnet scalar invariants. Specific functional forms of the related point-like Lagrangians are selected by Noether symmetries and we solve the corresponding field equations finding out exact cosmological solutions.

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