arXiv subjects

Vittorio De Falco

Publications and source records attributed to Vittorio De Falco.

At least 19 recordsLinked to original sources

arXiv2026

Confronting eikonal and post-Kerr methods with numerical evolution of scalar field perturbations in spacetimes beyond Kerr

The accurate computation of quasinormal modes from rotating black holes beyond general relativity is crucial for testing fundamental physics with gravitational waves. In this study, we assess the accuracy of the eikonal and post-Kerr approximations in predicting the quasinormal mode spectrum of a scalar field on a deformed Kerr spacetime. To obtain benchmark results and to analyze the ringdown dynamics from generic perturbations, we further employ a 2+1-dimensional numerical time-evolution framework. This approach enables a systematic quantification of theoretical uncertainties across multiple angular harmonics, a broad range of spin parameters, and progressively stronger deviations from the Kerr geometry. We then confront these modeling errors with simple projections of statistical uncertainties in quasinormal mode frequencies as a function of the signal-to-noise ratio, thereby exploring the domain of validity of approximate methods for prospective high-precision black-hole spectroscopy. We also report that near-horizon deformations can affect prograde and retrograde modes differently and provide a geometrical explanation.

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

Compact binary system dynamics at the second post-Newtonian order: analytical formula of the coordinate time for eccentric and circular orbits

This work is based on the letter Phys. Lett. B, 865, 139484 (2025), where we developed the analytical expression of the coordinate time in terms of the eccentric anomaly at the second post-Newtonian order in General Relativity for a compact binary system moving on eccentric orbits. The aim of this paper is to provide more details about the performed calculations and to produce other new results. More specifically, we will focus on deriving the analytical expression of the coordinate time at the second Post-Newtonian order for circular orbits and then discuss two astrophysical applications involving binary neutron star and black hole systems.

gr-qc↗

arXiv2025

Toward a unified view of agnostic parametrizations for deformed black holes

A variety of robust and effective descriptions have been devised to extract model-independent information about the fundamental properties of black holes from observational data when searching for deviations from general relativity. In this work, we construct explicit transformation maps establishing the equivalence among three relevant parametrizations for different spacetime patches: Johannsen-Psaltis, Rezzolla-Zhidenko, and Effective Metric Description. We then select representative black hole geometries to determine the minimal number of parameters required within each scheme to reproduce the associated quasi-normal mode spectra with a prescribed degree of accuracy. Our analysis shows that, for the given observables, a finite set of coefficients suffices to attain the desired precision in the three frameworks. Finally, we emphasize how the individual strengths of these effective descriptions can be exploited to probe complementary aspects of black hole physics.

gr-qc↗

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

Analytical coordinate time at the second post-Newtonian order

We derive the analytical expression of the coordinate time $t$ in terms of the eccentric anomaly $u$ at the second post-Newtonian order in General Relativity for a compact binary system moving on eccentric orbits. The parametrization of $t$ with $u$ permits to reduce at the minimum the presence of discontinuous trigonometric functions. This is helpful as they must be properly connected via accumulation functions to finally have a smooth coordinate time $t(u)$. Another difficulty relies on the presence of an infinite sum, about which we derive a compact form. This effort reveals to be extremely useful for application purposes. Indeed, we need to truncate the aforementioned sum to a certain finite threshold, which strongly depends on the selected parameter values and the accuracy error we would like to achieve. Thanks to our work, this analysis can be easily carried out.

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

Reconstruction of spider system's observables from orbital period modulations via the Applegate mechanism

Redback and black widow pulsars are two classes of peculiar binary systems characterized by very short orbital periods, very low mass companions, and, in several cases, regular eclipses in their pulsed radio signal. Long-term timing revealed systematic but unpredictable variations in the orbital period, which can most likely be explained by the so-called Applegate mechanism. This relies on the magnetic dynamo activity generated inside the companion star and triggered by the pulsar wind, which induces a modification of the star's oblateness (or quadrupole variation). This, in turn, couples with the orbit by gravity, causing a consequent change in the orbital period. The Applegate description limits to provide estimates of physical quantities by highlighting their orders of magnitude. Therefore, we derive the time-evolution differential equations underlying the Applegate model, that is, we track such physical quantities in terms of time. Our strategy is to employ the orbital period modulations, measured by fitting the observational data, and implementing a highly accurate approximation scheme to finally reconstruct the dynamics of the spider system under study and the relative observables. Among the latter is the magnetic field activity inside the companion star, which is still a matter of debate for its complex theoretical modeling and the ensuing expensive numerical simulations. As an application, we exploit our methodology to examine two spider sources: 47 Tuc W (redback) and 47 Tuc O (black widow). The results obtained are analyzed and then discussed with the literature.

astro-ph.HE↗

arXiv2025

Can wormholes mirror the quasi-normal mode spectrum of Schwarzschild black holes?

Wormholes are exotic compact objects characterized by the absence of essential singularities and horizons, acting as slender bridges linking two distinct regions of spacetime. Despite their theoretical significance, they remain however undetected, possibly due to their ability to closely mimic the observational properties of black holes. This study explores whether a static and spherically symmetric wormhole within General Relativity can reproduce the quasi-normal mode spectrum of a Schwarzschild black hole under scalar, electromagnetic, and axial gravitational perturbations, both individually and in combination. To address this, we reformulate the wormhole metric components using a near-throat parametrization. Our analysis concentrates on the fundamental mode and first overtone, estimated via the Wentzel-Kramers-Brillouin method. By employing a customized minimization strategy, we demonstrate that within a specific region of the parameter space, a wormhole can successfully replicate a subset of the black hole quasi-normal mode spectrum.

gr-qc↗

arXiv2024

Fully metallic geodesic lenses as analog electromagnetic models of static and spherically symmetric gravitational fields

We demonstrate that a fully metallic and air-filled geodesic waveguide can be employed as an analog electromagnetic model of a static and spherically symmetric gravitational field. By following the Plebanski formalism, a space-time metric of the aforementioned type is firstly encoded into the electromagnetic properties of a flat space-time region in the form of an isotropic and radially varying refractive index distribution. Then, a three-dimensional, air-filled, and axially symmetric waveguide, composed of two equally spaced and curved metallic surfaces, is employed. Its shape is tailored such that the effective paths, followed by transverse electromagnetic beams of microwave radiation within this waveguide, result equivalent to null-geodesics taking place in the aforementioned refractive medium. This strategy avoids the need for a refractive medium, although it only allows to reproduce the space-time metric on the invariant plane. Two analog electromagnetic models of gravity, using the proposed approach, are designed to reproduce the metric of both a Schwarzschild black hole and a Morris-Thorne wormhole. The results from full-wave simulations demonstrate that a one-dimensional Gaussian beam faithfully follows a path completely equivalent to general relativistic null geodesics with a mean relative error within 4%.

gr-qc↗

arXiv2024

Radiative losses and radiation-reaction effects at the first post-Newtonian order in Einstein-Cartan theory

Gravitational radiation-reaction phenomena occurring in the dynamics of inspiralling compact binary systems are investigated at the first post-Newtonian order beyond the quadrupole approximation in the context of Einstein-Cartan theory, where quantum spin effects are modeled via the Weyssenhoff fluid. We exploit balance equations for the energy and angular momentum to determine the binary orbital decay until the two bodies collide. Our framework deals with both quasi-elliptic and quasi-circular trajectories, which are then smoothly connected. Key observables like the laws of variation of the orbital phase and frequency characterizing the quasi-circular motion are derived analytically. We conclude our analysis with an estimation of the spin contributions at the merger, which are examined both in the time domain and the Fourier frequency space through the stationary wave approximation.

gr-qc↗

arXiv2023

Static and spherically symmetric wormholes in metric-affine theories of gravity

We consider static and spherically symmetric wormhole solutions in extended metric-affine theories of gravity supposing that stability and traversability of these objects can be achieved by means of the geometric degrees of freedom. In particular, we consider $f(R)$ metric, $f(T)$ teleparallel, and $f(Q)$ symmetric teleparallel models where curvature, torsion, and non-metricity rule entirely the background geometry without invoking any exotic energy-momentum tensor as matter field source. Starting from the flaring out and null energy conditions, we gather together a series of constraints which allow us to state that stable and traversable wormholes can be derived in a purely geometric approach resorting to modified gravity theories with more degrees of freedom than general relativity.

gr-qc↗

arXiv2023

The role of the boundary term in $f(Q,B)$ symmetric teleparallel gravity

In the framework of metric-affine gravity, we consider the role of the boundary term in Symmetric Teleparallel Gravity assuming $f(Q,B)$ models where $f$ is a smooth function of the non-metricity scalar $Q$ and the related boundary term $B$. Starting from a variational approach, we derive the field equations and compare them with respect to those of $f(Q)$ gravity in the limit of $B\to0$. It is possible to show that $f(Q,B)=f(Q-B)$ models are dynamically equivalent to $f(R)$ gravity as in the case of teleparallel $f(\tilde{B}-T)$ gravity (where $B\neq \tilde{B}$). Furtherrmore, conservation laws are derived. In this perspective, considering boundary terms in $ f(Q)$ gravity represents the last ingredient towards the Extended Geometric Trinity of Gravity, where $f(R)$, $f(T,\tilde{B})$, and $f(Q,B)$ can be dealt with under the same standard. We also compare and discuss about the Gibbons-Hawking-York boundary term of General Relativity and the boundary term $B$ in $f(Q,B)$ gravity.

gr-qc↗

arXiv2023

Analytical results for binary dynamics at the first post-Newtonian order in Einstein-Cartan theory with the Weyssenhoff fluid

The quantum spin effects inside matter can be modeled via the Weyssenhoff fluid, which permits to unearth a formal analogy between general relativity and Einstein-Cartan theory at the first post-Newtonian order. In this framework, we provide some analytical formulas pertaining to the dynamics of binary systems having the spins aligned perpendicular to the orbital plane. We derive the expressions of the relative orbit and the coordinate time, which in turn allow to determine the gravitational waveform, and the energy and angular momentum fluxes. The potentialities of our results are presented in two astrophysical applications, where we compute: ($i$) the quantum spin contributions to the energy flux and gravitational waveform during the inspiral phase; ($ii$) the macroscopic angular momentum of one of the bodies starting from the time-averaged energy flux and the knowledge of few timing parameters.

gr-qc↗

arXiv2023

Epicyclic frequencies in the equatorial plane around stationary and axially symmetric wormhole geometries

Epicyclic frequencies are usually observed in X-ray binaries and constitute a powerful astrophysical mean to probe the strong gravitational field around a compact object. We consider them in the equatorial plane around a general stationary and axially symmetric wormhole. We first search for the wormholes' existence, distinguishing them from a Kerr black hole. Once there will be available observational data on wormholes, we present a strategy to reconstruct the related metrics. Finally, we discuss the implications of our approach and outline possible future perspectives.

gr-qc↗

arXiv2023

Exploring departures from Schwarzschild black hole in $f(R)$ gravity

Different astrophysical methods can be combined to detect possible deviations from General Relativity. In this work, we consider a class of $f(R)$ gravity models selected by the existence of Noether symmetries. In this framework, it is possible to determine a set of static and spherically symmetric black hole solutions, encompassing small departures from the Schwarzschild geometry. In particular, when gravity is the only dominating interaction, we exploit the ray-tracing technique to reconstruct the image of a black hole, the epicyclic frequencies, and the black hole shadow profile. Moreover, when matter dynamics is also affected by an electromagnetic radiation force, we take into account the general relativistic Poynting-Robertson effect. In light of the obtained results, the proposed strategy results to be robust and efficient: on the one hand, it allows to investigate gravity from strong to weak field regimes; on the other hand, it is capable of detecting small departures from General Relativity, depending on the current observational sensitivity.

gr-qc↗