arXiv subjects

Davi C. Rodrigues

Publications and source records attributed to Davi C. Rodrigues.

At least 19 recordsLinked to original sources

arXiv2026

Test-particle dynamics in a noncommutative deformation of Einstein-Rosen waves

We investigate phenomenological effects induced by a noncommutative deformation of Einstein--Rosen gravitational-waves within the framework of the Riemannian geometry of noncommutative surfaces developed by Chaichian et al. Considering a noncommutative structure between the radial and axial coordinates, we study perturbatively the motion of nonrelativistic test particles in the corresponding deformed geometry. We show that the deformation generates a coupling between the radial and longitudinal sectors, while the radial dynamics remains unaffected by the noncommutative deformation at the perturbative order considered. The induced longitudinal response is governed by a spectrally weighted functional of the gravitational-wave profile, implying that longitudinal observables depend on higher-order spectral moments than their commutative radial counterparts. As a consequence, noncommutative effects exhibit enhanced sensitivity to the ultraviolet structure of the gravitational configuration. We analyze separately monochromatic Einstein--Rosen waves and the localized Weber--Wheeler pulse. In the monochromatic case, the noncommutative correction induces a quasi-periodic longitudinal motion, whereas for the Weber--Wheeler pulse it produces an impulsive longitudinal response analogous to a gravitational velocity memory effect. In addition, we derive an explicit analytical expression in commutative General Relativity for the residual radial velocity generated by the Weber--Wheeler pulse at large radial distances in the perturbative regime.

gr-qc↗

arXiv2026

Cosmologically Coupled Black Holes with Regular Horizons

We present the most general and exact solution of Einstein's gravity sourced by an anisotropic fluid describing the cosmological embedding (CE) of a static and spherically-symmetric object, including black holes (BHs) or exotic compact objects, without radial energy influx and in an arbitrary Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmology. This is done fully considering backreaction of the local geometry on the cosmological dynamics. Our solution is free of curvature singularities at the would-be BH event horizon, thus solving a main issue of the CE of BH solutions proposed so far. As a byproduct, we derive a new CE of the Schwarzschild BH - distinct from McVitties's original proposal - that is regular everywhere except at the central singularity.

gr-qc↗

arXiv2026

Gravitational waveforms from inspiraling compact binaries in quadratic gravity and their parameterized post-Einstein characterization

We investigate gravitational waveforms from the inspiral phase of compact binary systems within the framework of quadratic gravity and map their deviations from general relativity into the parameterized post-Einstein (PPE) formalism to constrain the theory parameters. Quadratic gravity generically includes a massive spin-2 ghost, which leads to ill-defined energy and angular momentum fluxes. Following earlier proposals, we remove these unphysical features by imposing a constraint on the massive spin-2 mode, restricting it to propagate only the same polarizations of general relativity. Within the quadrupole approximation, we derive the radiative degrees of freedom, including massless and massive tensor modes, as well as a massive scalar field. Using the stationary phase approximation, we compute the Fourier-domain waveform of the massless tensor modes and extract the phase corrections. For small deviations from general relativity, we show that both the scalar and massive tensor modes can be consistently embedded into the PPE framework, extending previous results that considered only scalar fields. We derive updated constraints on the parameters of quadratic gravity, finding bounds improved by several orders of magnitude compared to existing limits. Finally, we present forecasts for the sensitivity of the Einstein Telescope to these deviations.

gr-qc↗

arXiv2025

Probing the origin of the kilonova candidate GRB 230307A: analysis of host galaxy and offset

We investigate the host galaxy of the long gamma-ray burst GRB 230307A, which is associated with a kilonova candidate likely produced by a binary neutron-star (BNS) merger. The transient occurred at a projected offset of ~40 kpc from its host. We consider two explanations for this large distance: (i) NSs that merge inside a remote globular cluster, or (ii) a BNS that formed in the disk whose orbit was strongly modified by the NS natal kicks. Using JWST data and comparisons with known globular clusters, we show that a globular-cluster origin is unlikely. Using JWST and MUSE data, we derive the host galaxy morphology, stellar mass, estimate the atomic gas (HI+He) contribution, and the host rotation curve. Assuming an NFW halo and applying Bayesian inference, we obtain a mass model for the host. From this model, we compute the time required for a disk-formed BNS, with a given natal kick, to reach the observed offset while marginalizing over uncertainties and over the initial position in the disk. We compare these results with BNS-merger simulations from a population-synthesis code combined with stellar evolutionary tracks, which provide the coalescence time and kick velocity for each realization. The two approaches have an overlap in the kick-time diagram, but only 0.1% of the simulated systems is compatible with the galaxy-mass model. This indicates that a disk origin is possible, but requires fine-tuned conditions for the kilonova to occur at such a large distance from the host galaxy.

astro-ph.HE↗

arXiv2025

Schwarzschild-de Sitter spacetime in regular coordinates with cosmological time

Starting from the Einstein equations in Schwarzschild-de Sitter (SdS) spacetime and imposing Friedmann-Robertson-Walker coordinates at large distances, we find two coordinate systems with time-dependent metrics that are smooth across both the black hole and cosmological horizons. These coordinates require a positive cosmological constant for regularity, and thus they are not de Sitter extensions of the Kruskal-Szekeres or Israel coordinates. One of the coordinate systems was only found in 1999 (Abbassi coordinates), and it has led to conflicting interpretations in the literature, while the other was briefly commented on and promptly dismissed as unphysical or incompatible with SdS. We derive that the second solution is equivalent to the first one, and that both are indeed equivalent descriptions of SdS spacetime. We also derive explicit coordinate transformations linking these coordinate systems to the Kottler coordinates and the maximally extended Lake-Israel coordinates. Among other applications, these results, which extend the largely used cosmological and local coordinates, should be useful for further developments in understanding the exact interplay between black holes and the cosmological background, which has been the focus of a number of recent works.

gr-qc↗

arXiv2025

Gauges for quadratic gravity: the extended transverse gauge and the energy-momentum tensor of the massive spin-2 field

We study the 4D Einstein-Hilbert action extension based on the square of the curvature tensors. Analyses of gauge and perturbation modes are often done considering the Teyssandier gauge condition. Although this approach can be useful for other higher-order extensions of quadratic gravity, a generalized transverse (or Lorentz) gauge is clear and sufficient for the present case, as explained here. We provide a detailed analysis of the generalized transverse gauge condition, its residual gauge symmetry, the physical modes, the induced energy-momentum tensor (EMT) of the massive spin-2 mode (which is gauge-dependent), and a comparison with the Teyssandier gauge. The derivation is valid for any EMT. We also compare the induced EMT in quadratic gravity with the massive spin-2 Fierz-Pauli EMT, which is different from the previous cases. The comparison is further developed by considering a spherical isothermal sphere, which works as an approximation to virialized spherical systems.

gr-qc↗

arXiv2025

Line-of-sight acceleration as a test of the Galactic Yukawa potential

We forecast the impact of direct radial acceleration measurements, based on two redshift measurements of the same target one decade apart, on constraining the Yukawa correction to the Newtonian potential in the Milky Way. The Galaxy's matter distribution is modeled as the sum of a spherical bulge, a spherical dark matter halo, and two axially symmetric disks. Considering a sample of 165 Milky Way globular clusters, we find that the precision of next-generation spectrographs ($\sim$ 10 cm s$^{-1}$) is not sufficient to provide competitive constraints compared to rotation curve data using the same baryonic matter distribution. The latter sample only becomes competitive for a precision better than 0.6 cm s$^{-1}$. On the other hand, we find that adopting a population of $1.3 \times 10^5$ RR Lyrae stars as targets, a precision of $\sim$ 10 cm s$^{-1}$ can achieve constraints on the Yukawa parameters as strong as with the rotation curves.

astro-ph.GA↗

arXiv2025

Scale-dependent and background-preserving gravity from an action: cosmological tests

We investigate the observational implications of a gravitational model wherein the gravitational constant $G$ and the cosmological constant $Λ$ exhibit scale-dependent behavior at the perturbative level, while preserving the General Relativity (GR) field equations at the background. This model is motivated by the potential influence of large-scale (infrared) Renormalization Group (RG) corrections to gravity and is constructed upon an effective action incorporating a scale definition via Lagrange multipliers. We explore the effects of these modifications during the recombination epoch with particular focus on their impact on the structure of acoustic oscillations. Additionally, we perform a comprehensive parameter fitting analysis using data from the Cosmic Microwave background (CMB), type Ia Supernovae (SN Ia), Baryon Acoustic Oscilations (BAO) and Redshift Space Distortions (RSD). Our results indicate that the RG corrections here considered are consistent with the main predictions of the $Λ$CDM model, and they slightly increase the uncertainties in the parameter estimations. Such small differences cannot be used to dismiss the current cosmological tensions. Although previous results indicated that this model is more flexible than $Λ$CDM regarding RSD data, potentially alleviating tensions, this advantage becomes negligible with the current extended data set. The framework maintains its theoretical consistency and foundation; however, unless further generalized, it cannot effectively address current cosmological issues.

gr-qc↗

arXiv2024

Cosmological coupling of local gravitational systems

We investigate the cosmological coupling of spherical, local astrophysical systems. We derive a general formula quantifying the cosmological coupling of the Misner-Sharp mass of these objects. We show that, in the weak-field limit, the cosmological coupling is only allowed if there are pressure anisotropies. We also apply our results to galaxies, modelling them with the Navarro-Frenk-White and Einasto profiles. We show that the galactic mass can be coupled to the cosmological dynamics and examine its dependence on the scale factor of the universe.

gr-qc↗

arXiv2024

Scale-dependent cosmology from effective quantum gravity in the invariant framework

We explore the possibility of a consistent cosmology based on the gauge-fixing independent running of the gravitational and cosmological constants ($G$ and $Λ$) in the framework of effective quantum gravity. In particular, their running in this framework was found to satisfy $G \propto Λ^4$. In the cosmological setting, the covariance of the theory provides energy conservation relations, which are impossible to satisfy with the unique scale parameter. However, by introducing the second sub-dominant scale corresponding to the higher-loop corrections and higher-derivative terms, one can close the system of equations for the running of parameters and arrive at the consistent cosmological solutions. This approach yields a change in the cosmological expansion history that affects the ratio of the Hubble parameter today to the Hubble parameter at high redshift.

gr-qc↗

arXiv2024

A detailed first-order post-Newtonian analysis of massive Brans-Dicke theories: numerical constraints and the $β$ parameter meaning

Massive Brans-Dicke (BD) theory is among the simplest general relativity extensions. It is commonly found as the weak-field limit of other gravitational theories. Here we do a detailed post-Newtonian analysis of massive BD theories. We start by expanding the massive BD field equations following the Will-Nodtvedt Parameterized-Post-Newtonian (PPN) formalism, without point-particle approximations. A single potential that is not present in the standard PPN formalism is found. This new potential hinders immediate PPN conclusions. To proceed, we do a complete first-order post-Newtonian analysis and explicitly derive all the conserved quantities. After demanding that there exists a Newtonian limit by requiring the BD mass to be sufficiently large, we find, as expected, that $γ= 1$; but there is no effective $β$ parameter that can have the same physical role of the standard $β$ in PPN formalism. All the others standard PPN parameters can be extended to the massive BD case without issues and are shown to have the same values of general relativity. At last, we consider numerical relations on the periastron advance and the BD mass in two different physical contexts, the orbit of Mercury about the Sun and the orbit of the star S2 about the expected supermassive black hole in the Milky Way.

gr-qc↗

arXiv2024

Constraints on cosmologically coupled black holes from gravitational wave observations and minimal formation mass

We test the possibility that the black holes (BHs) detected by LIGO-Virgo-KAGRA (LVK) may be cosmologically coupled and grow in mass proportionally to the cosmological scale factor to some power $k$, which may also act as the dark energy source if $k\approx 3$. This approach was proposed as an extension of Kerr BHs embedded in cosmological backgrounds and possibly without singularities or horizons. In our analysis, we develop and apply two methods to test these cosmologically coupled BHs (CCBHs) either with or without connection to dark energy. We consider different scenarios for the time between the binary BH formation and its merger, and we find that the standard log-uniform distribution yields weaker constraints than the CCBH-corrected case. Assuming that the minimum mass of a BH with stellar progenitor is $2M_\odot$, we estimate the probability that at least one BH among the observed ones had an initial mass below this threshold. We obtain these probabilities either directly from the observed data or by assuming the LVK power-law-plus-peak mass distribution. In the latter case we find, at $2σ$ level, that $k < 2.1$ for the standard log-uniform distribution, or $k < 1.1$ for the CCBH-corrected distribution. Slightly weaker bounds are obtained in the direct method. Considering the uncertainties on the nature of CCBHs, we also find that the required minimum CCBH mass value to eliminate the tensions for $k=3$ should be lower than 0.5 $M_\odot$ (again at 2$σ$). Finally, we show that future observations have the potential to decisively confirm these bounds.

astro-ph.CO↗

arXiv2023

Palatini $f(R)$ gravity tests in the weak field limit: Solar System, seismology and galaxies

Palatini $f(R)$ gravity is probably the simplest extension of general relativity (GR) and the simplest realization of a metric-affine theory. It has the same number of degrees of freedom as GR and, in vacuum, it is straightforwardly mapped into GR with a cosmological constant. The mapping between GR and Palatini $f(R)$ inside matter is possible but at the expense of reinterpreting the meaning of the matter fields. The physical meaning and consequences of such mapping will depend on the physical context. Here we consider three such cases within the weak field limit: Solar System dynamics, planetary internal dynamics (seismology), and galaxies. After revising our previous results on the Solar System and Earth's seismology, we consider here the possibility of $f(R)$ Palatini as a dark matter candidate. For any $f(R)$ that admits a polynomial approximation in the weak field limit, we show here, using SPARC data and a recent method that we proposed, that the theory cannot be used to replace dark matter in galaxies. We also show that the same result applies to the Eddington-inspired Born-Infeld gravity. Differently from the metric $f(R)$ case, the rotation curve data are sufficient for this conclusion. This result does not exclude a combination of modified gravity and dark matter.

gr-qc↗

arXiv2023

Normalized additional velocity distribution: testing the radial profile of dark matter halos and MOND

We propose a complementary and fast approach to study galaxy rotation curves directly from the sample data, instead of individual fits. With this approach, some relevant tests can be done analytically. It is based on a dimensionless difference between the observational rotation curve and the expected one from the baryonic matter ($δV^2$) as a function of the normalized radius $r_n$ (i.e., for all galaxies, $0 < r_n < 1$). Using 153 galaxies from the SPARC galaxy sample, we find the observational distribution of $δV^2$. Considering radii with $0.2 < r_n < 0.9$, most of the SPARC data are close to the curve $δV^2 = r_n^{0.42}$, and about $95\%$ of the SPARC data is between the curves $δV^2 = r_n^{2.2}$ and $δV^2 = 2 r_n^{0.38} - r_n^{1.9} $. We consider three well known dark matter halo models (NFW, Burkert and DC14), a simple dark matter rotation curve profile for the purpose of model comparison (Arctan$_α$) and one modified gravity model without dark matter (MOND). By comparing the observational data distribution with the model-inferred data, we confirm that the NFW halo lacks the necessary diversity to reproduce several observed rotation curves, while Burkert and DC14 models have better concordance with observational data. The lowest $δV^2$ curves that can be found from NFW are linear on the normalized radius (i.e., $δV^2_{NFW} = r_n$), while for Burkert $δV^2_{Bur} = r_n^2$ (this result is independent of the halo density parameter, i.e., $ρ_{c}$ or $ρ_{s}$). MOND only covers the very central region of the observed distribution, hence it also lacks the necessary diversity, which in turn is related to larger $χ^2$ values. In a second paper, the method will be extended to consider other classes of modified gravity models.

astro-ph.GA↗

arXiv2023

On Rastall gravity formulation as a $f(R,\mathcal{L}_m)$ and a $f(R,T)$ theory

Rastall introduced a stress-energy tensor whose divergence is proportional to the gradient of the Ricci scalar. This proposal leads to a change in the form of the field equations of General Relativity, but it preserves the number of degrees of freedom. Rastall's field equations can be either interpreted as GR with a redefined SET, or it can imply different physical consequences inside the matter sector. We investigate limits under which the Rastall field equations can be directly derived from an action, in particular from two $f(R)$-gravity extensions: $f(R,\mathcal L_m)$ and $f(R,T)$. We show that there are similarities between these theories, but the Rastall SET cannot be fully recovered from them, apart from certain particular cases here discussed. It is remarkable that a simple, covariant and invertible redefinition of the SET, as the one proposed by Rastall, is hard to be directly implemented in the action.

gr-qc↗

arXiv2022

Primordial perturbations and inflation in holographic cosmology

We consider an inflationary scenario in the holographic braneworld with a cosmological fluid occupying the 3+1 dimensional brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The contribution of the boundary conformal field can be represented as a modification of Einstein's equations on the boundary. Using these effective Einstein equations we calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-essence type of inflaton. We find that the braneworld scenario affects the scalar power spectrum only in the speed of sound dependence on the slow-roll parameters whereas there is no change in the tensor power spectrum. This implies that the changes in the spectral indices appear at the second order in the slow-roll parameter expansion.

gr-qc↗

arXiv2022

Primordial perturbations and inflation in a holography inspired Gauss-Bonnet cosmology

We consider an action for gravity that, in addition to the Einstein-Hilbert term, contains a function of the Ricci scalar and the Gauss-Bonnet invariant. The specific form of the function considered is motivated by holographic cosmology. At background level the field equations imply modified Friedmann equations of the same form as those in the holographic cosmology. We calculate the cosmological perturbations and derive the corresponding power spectra assuming a general $k$-inflation. We find that the resulting power spectra differ substantially from those obtained in both holographic and standard cosmology. The estimated spectral index and tensor-to-scalar ratio are confronted with the Planck results.

gr-qc↗

arXiv2021

Post-Newtonian $γ$-like parameters and the gravitational slip in scalar-tensor and $f(R)$ theories

We review the fundamentals and highlight the differences between some commonly used definitions for the PPN gamma parameter ($γ$) and the gravitational slip ($η$). Here we stress the usefulness of a gamma-like parameter used by Berry and Gair ($γ_{\scriptscriptstyle Σ}$) that parametrizes the bending of light and the Shapiro time delay in situations in which the standard $γ$ cannot be promptly used. First we apply our considerations to two well known cases, but for which some conflicting results can be found: massive Brans-Dicke gravity and $f(R)$ gravity (both the metric and the Palatini versions). Although the slip parameter is always well defined, it has in general no direct relation to either light deflection or the Shapiro time delay, hence care should be taken on imposing the PPN $γ$ bounds on the slip. We stress that, for any system with a well posed Newtonian limit, Palatini $f(R)$ theories always have $γ= 1$; while metric $f(R)$ theories can only have two values: either 1 or 1/2. The extension towards Horndeski gravity shows no qualitative surprises, and $γ_{\scriptscriptstyle Σ}$ is a constant in this context (only assuming that the Horndeski potentials can be approximated by analytical functions). This implies that a precise study on the bending of light for different impact parameters can in principle be used to rule out the complete Horndeski action as an action for gravity. Also, we comment on the consequences for $γ$ inferences at external galaxies.

gr-qc↗