arXiv subjects

Rocco D'Agostino

Publications and source records attributed to Rocco D'Agostino.

At least 19 recordsLinked to original sources

arXiv2026

Distance duality relation in symmetric teleparallel gravity

In this work, we investigate the distance duality relation (DDR) in symmetric teleparallel theories, where gravity is mediated by nonmetricity. Starting from the general metric-affine formulation and adopting the geometrical optics approximation, we show that the standard Etherington reciprocity relation remains valid in the presence of nonmetricity when electromagnetism is minimally coupled and the photon number is conserved. We then extend the analysis to a class of $f(Q)$ theories with a nonminimal coupling between the electromagnetic field and the nonmetricity scalar. We demonstrate that such an interaction modifies the conservation of the photon number current, leading to a dynamical violation of the DDR. Focusing on a homogeneous and isotropic spacetime background in the coincident gauge, we derive a generalized DDR formula that directly relates observational distance measures to the Hubble expansion rate. Furthermore, we discuss the link between the deviations from Etherington's relation and variations of the effective fine-structure constant. Specific illustrative examples of the coupling function are also analyzed, showing that phenomenologically viable models predict only small deviations from the standard DDR. Our results provide a unified framework to distinguish between the geometric and dynamical origins of DDR violations, opening new avenues for testing non-Riemannian gravity with future high-precision astrophysical and cosmological observations.

gr-qc↗

arXiv2026

From minimal-length quantum theory to modified gravity

In this work, we consider generalized uncertainty principles (GUPs) that incorporate a minimal length through generic momentum-dependent deformation functions. We thus develop a systematic approach connecting such a framework to effective gravitational actions extending general relativity. By examining quantum gravity-motivated corrections to black hole entropy induced by the GUP and employing Wald's formalism, we reconstruct modifications to Einstein's gravity within the contexts of $f(R)$ and $f(R, R_{μν} R^{μν})$ theories. In this way, we establish a direct mapping between the GUP parameters and the higher-order curvature coefficients in the gravitational Lagrangian. As an illustrative application, we compute corrections to the general relativistic prediction for light deflection, which in turn allows us to infer a stringent upper bound on the minimal measurable length. Our results show that GUP-induced effects can be consistently embedded into extended gravity theories, offering a promising framework for testing quantum gravity phenomenology through astrophysical and cosmological observations.

gr-qc↗

arXiv2026

Observational constraints on nonlocal black holes via gravitational lensing

In this paper, we study the gravitational lensing around the static and spherically symmetric DD black holes, which we recently derived as perturbations of the Schwarzschild geometry within the revised Deser-Woodard theory of nonlocal gravity. We first present general analytical expressions for the deflection angle in both weak- and strong-deflection limits, explicitly relating them to the nonlocal corrections to Schwarzschild spacetime. Subsequently, we analyze lensing observables, such as the post-Newtonian effects and the black hole shadow, to constrain the DD black hole parameter space using current observational bounds. Finally, we perform a joint statistical analysis based on the Fisher information matrix, combining these findings with our previously obtained constraints from quasinormal modes. Our results indicate consistency with general relativity at the $1.13σ$ level. This work provides a first assessment of the DD parameter space and offers new insights to probe deviations from Einstein's gravity in view of future larger datasets.

gr-qc↗

arXiv2026

Gravitational perturbations of nonlocal black holes

We derive the master equations governing axial and polar gravitational perturbations of a generic static and spherically symmetric black hole spacetime within the framework of the revised Deser--Woodard nonlocal gravity theory. We then apply our general formalism to a one-parameter family of black hole solutions recently obtained by the present authors, representing small first-order deviations from the Schwarzschild geometry. We provide well-motivated arguments that allow us to render the analysis analytically tractable. Our results provide the first complete perturbative characterization of nonlocal black holes and lay the groundwork for future investigations.

gr-qc↗

arXiv2025

Distinguishing Distance Duality breaking models using electromagnetic and gravitational waves measurements

Several assumptions at the foundation of the standard cosmological model have as a direct consequence a specific relation between cosmological distances, known as the distance duality relation, whose violation would be a smoking gun of deviations from standard cosmology. We explore the role of upcoming gravitational wave observations in investigating possible deviations from the distance duality relation, alongside the more commonly used supernovae. We find that, when combined with baryon acoustic oscillations, gravitational waves will provide similar constraining power to the combination of baryon acoustic oscillations and supernovae. Moreover, the combination of observables with different sensitivities to electromagnetic and gravitational physics provides a promising way to discriminate among different physical mechanisms that could lead to violations of the distance duality relation.

astro-ph.CO↗

arXiv2025

Quasinormal modes of nonlocal gravity black holes

We present a comprehensive study of the quasinormal modes of a new class of nonlocal static and spherically symmetric black hole (BH) solutions within the framework of the revised Deser-Woodard theory of gravity. These solutions are constructed as linear perturbations of the Schwarzschild spacetime and are characterized by an inverse power-law behavior of the lapse metric function. We derive the radial profiles of the effective potentials corresponding to scalar, electromagnetic and axial gravitational fluctuations on the BH background. Using the WKB method, complemented by Padé approximants to regularize the trend of the effective potential near its peak, we compute the complex quasinormal mode frequencies associated with each type of perturbation. Our results are examined from both mathematical and physical perspectives, and are substantiated with references to existing literature. In particular, we compare the numerical outcomes with the predictions of the Schwarzschild metric to quantify deviations from the framework of general relativity. When all types of perturbations are combined, the relative deviations of the fundamental modes can reach up to $\sim 12\%$. Finally, we discuss the possibility to place observational bounds in the BH parameter space, based on the predicted sensitivities of future gravitational wave detectors.

gr-qc↗

arXiv2025

Black hole solutions in the revised Deser-Woodard nonlocal theory of gravity

We consider the revised Deser-Woodard model of nonlocal gravity by reformulating the related field equations within a suitable tetrad frame. This transformation significantly simplifies the treatment of the ensuing differential problem while preserving the characteristics of the original gravitational theory. We then focus on static and spherically symmetric spacetimes in vacuum. Hence, we demonstrate that the gravitational theory under study admits a class of black hole solutions characterized by an inverse power-law correction to the Schwarzschild $g_{tt}$ metric function and a first-order perturbation of the $g_{rr}$ Schwarzschild component. Then, through a stepwise methodology, we analytically solve the full dynamics of the theory, finally leading to the reconstruction of the nonlocal distortion function, within which the new black hole solutions arise. Furthermore, we analyze the geometric properties of the obtained solutions and quantify the deviations from the Schwarzschild prediction. This work provides new insights into compact object configurations and advances our understanding of nonlocal gravity theories in the strong-field regime at astrophysical scales.

gr-qc↗

arXiv2025

Teleparallel dark energy in a nonflat universe

In this paper, we investigate the cosmological dynamics of teleparallel dark energy in the presence of nonzero spatial geometry. Extending previous analyses of nonminimal scalar-tensor theories in the torsion-based framework, we consider different scalar field potentials and examine the resulting background evolution and linear perturbations. Adopting a dynamical systems approach, we reformulate the field equations and constrain the model parameters via a Markov chain Monte Carlo analysis combining updated datasets from Pantheon+SH0ES supernovae, cosmic chronometers, and growth rate measurements. Our results suggest a mild preference for an open geometry, although all models remain consistent with a flat universe at the $1σ$ level. Notably, Bayesian information criteria indicate that the nonflat teleparallel scenario with a vanishing potential is strongly favored over the standard $Λ$CDM model. Furthermore, all teleparallel scenarios are compatible with local determinations of the Hubble constant and exhibit better agreement with low-redshift structure formation data compared to $Λ$CDM. These findings highlight the potential of nonflat teleparallel gravity to address current observational tensions and motivate its further investigation as a viable alternative to standard cosmology.

gr-qc↗

arXiv2025

Nonlocal gravity in a proper tetrad frame: traversable wormholes

We investigate the revised Deser-Woodard model of nonlocal gravity involving four auxiliary scalar fields, introduced to explain the standard cosmological background expansion history without fine-tuning issues. In particular, we simplify the complex field equations within a proper tetrad frame, thereby recasting the original system into a more tractable equivalent differential problem. We show that, by initially postulating the form of the $g_{tt}$ metric component, it is possible to reconstruct the distortion function of the gravitational model. We then describe a step-by-step procedure for solving the vacuum field equations in the case of a static and spherically symmetric spacetime. We apply our technique to find new traversable wormholes supported purely by gravity by employing either analytical, perturbative, or numerical methods. Furthermore, we demonstrate that the role of the nonlocal effects is analogous to that of exotic matter in general relativity, owing to their quantum nature. Finally, we discuss the main geometric properties of the obtained solutions. Our results present a feasible avenue for identifying novel compact objects while enhancing the comprehension of nonlocal gravitational theories.

gr-qc↗

arXiv2025

New limits on warm inflation from pulsar timing arrays

In this paper, we investigate scalar-induced gravitational waves (GWs) generated in the post-inflationary universe to infer new limits on warm inflation. We specifically examine the evolution of primordial GWs by scalar perturbations produced during the radiation-dominated epoch. For this purpose, we assume a weak regime of warm inflation under the slow-roll approximation, with a dissipation coefficient linearly dependent on the temperature of the radiation bath. We then derive analytical expressions for the curvature power spectrum and the scalar index, in the cases of chaotic and exponential potentials of the inflationary field. Subsequently, we compare the theoretical predictions regarding the relic energy density of GWs with the stochastic GW background signal recently detected by the NANOGrav collaboration through the use of pulsar timing array measurements. In so doing, we obtain numerical constraints on the free parameters of the inflationary models under study. Finally, we conduct a model selection analysis through the Bayesian inference method to measure the statistical performance of the different theoretical scenarios.

astro-ph.CO↗

arXiv2024

Geometric and topological corrections to Schwarzschild black hole

In this paper, we compute departures in the black hole thermodynamics induced by either geometric or topological corrections to general relativity. Specifically, we analyze the spherically symmetric spacetime solutions of two modified gravity scenarios with Lagrangians $\mathcal{L}\sim R^{1+ε}$ and $\mathcal{L}\sim R+ε\, \mathcal{G}^2$, where $\mathcal{G}$ is the Euler density in four dimensions, while $ 0<ε\ll 1$ measures the perturbation around the Hilbert-Einstein action. Accordingly, we find the expressions of the Bekenstein-Hawking entropy by the Wald formula, and the black hole temperature and horizon of the obtained solutions. We then investigate the heat capacities in terms of the free parameters of the theories under study. In doing so, we show that healing the problem of negative heat capacities can be possible under particular choices of the free constants, albeit with limitations on the masses allowed for the black hole solutions.

gr-qc↗

arXiv2024

Lagrangian formulation of the Tsallis entropy

We investigate the gravitational origin of the Tsallis entropy, characterized by the nonadditive index $δ$. Utilizing Wald's formalism within the framework of $f(R)$ modified theories of gravity, we evaluate the entropy on the black hole horizon for constant curvature solutions to the spherically symmetric vacuum field equations. In so doing, we demonstrate that the Tsallis entropy can be effectively derived from a generalization of the Lagrangian $\mathcal{L}\propto R^{1+ε}$, where $ε=δ-1$ quantifies small deviations from general relativity. In conclusion, we examine the physical implications of our findings in light of cosmological observations and elaborate on the possibility of solving the thermodynamic instability of Schwarzschild black holes.

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

Testing Yukawa cosmology at the Milky Way and M31 galactic scales

We address the galaxy rotation curves through the Yukawa gravitational potential emerging as a correction of the Newtonian potential in extended theories of gravity. On the one hand, we consider the contribution of the galactic bulge, galactic disk, and the dark matter halo of the Navarro-Frenk-White profile, in the framework of the standard $Λ$CDM model. On the other hand, we use modified Yukawa gravity to show that the rotational velocity of galaxies can be addressed successfully without the need for dark matter. In Yukawa gravity, we recover MOND and show that dark matter might be seen as an apparent effect due to the modification of the law of gravitation in terms of two parameters: the coupling constant $α$ and the characteristic length $λ$. We thus test our theoretical scenario using the Milky Way and M31 rotation velocity curves. In particular, we place observational constraints on the free parameters of Yukawa cosmology through the Monte Carlo method and then compare our results with the predictions of the $Λ$CDM paradigm by making use of Bayesian information criteria. Specifically, we find that $λ$ is constrained to be of the order of kpc, while cosmological data suggest $λ$ of the order of Gpc. To explain this discrepancy, we argue that there is a fundamental limitation in measuring $λ$ due to the role of quantum mechanics on cosmological scales.

astro-ph.CO↗

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

Reconstructing the distortion function of non-local cosmology: a model-independent approach

We consider non-local modifications of General Relativity given by a distortion function in terms of the inverse of the d'Alembert operator. The inclusion of these terms is motivated by the possibility of reproducing the current accelerated expansion of the Universe starting from non-local gravity. In particular, we propose a model-independent method, based on current observations, to reconstruct the shape of the distortion function, without resorting to a specific cosmological history. We describe a numerical procedure based on Padé polynomials that allows us to study the time evolution of the auxiliary scalar fields introduced to localize non-local gravity action. Thus, adopting suitable boundary conditions, we reconstruct the form of the non-local Lagrangian and infer the best analytical approximation of the numerical outcome. Furthermore, the distortion function turns on during the matter-dominated era, and its effects are delayed to the most recent cosmic times. This provides a natural explanation for the late cosmic acceleration, avoiding any fine-tuning problem of the cosmological constant. Finally, we compare our predictions with previous findings based on enforcing the standard $Λ$CDM background in the reconstruction process.

gr-qc↗

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

Cosmographic view on the $H_0$ and $σ_8$ tensions

Measurements of the $H_0$ and $σ_8$ parameters within the standard cosmological model recently highlighted significant statistical tensions between the cosmic microwave background and low-redshift probes, such as local distance ladder, weak lensing and galaxy clustering surveys. In this work, we frame geometrical distances in a model-independent way by means of cosmographic approximations in the range $z \in (0, 2.3)$ to take into account a robust dataset composed of Baryon Acoustic Oscillations (BAO), type Ia Supernovae (SN), Cosmic Chronometer (CC) data, and measurements from Redshift Space Distortions (RSD). From the joint analysis BAO\,+\,SN\,+\,CC\,+\,RSD, we find an accuracy of $\sim$1.4\% and $\sim$3.7\% on $H_0$ and $σ_8$, respectively. Our result for $H_0$ is at 2$σ$ tension with local measurements by the SH0ES team, while our $σ_8$ estimate is at 2.6$σ$ tension with Planck-CMB analysis. This inference shows a tension statistically smaller when compared to those estimated via the $Λ$CDM model. We also find that the jerk parameter can deviate more than 3$σ$ from the $Λ$CDM prediction. Under the same cosmographic setup, we also present results by considering a SH0ES Gaussian prior on $H_0$ that allows for improved accuracy of the parameter space of the models. The present work brings observational constraints on $H_0$ and $σ_8$ into a new model-independent perspective, which differs from the predictions obtained within the $Λ$CDM paradigm.

astro-ph.CO↗