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Abraão J. S. Capistrano

Publications and source records attributed to Abraão J. S. Capistrano.

16 recordsLinked to original sources
arXiv2026

Probing dynamical dark energy with late-time data: Evidence, tensions, and the limits of the $w_0w_a$CDM framework

We test the dynamical dark-energy $w_0w_a$CDM (CPL) framework against $Λ$CDM using CMB anisotropies and lensing together with DESI DR2, SDSS-IV, transverse/angular BAO (BAOtr), and Cepheid-calibrated PantheonPlus SN~Ia data. CPL inferences are strongly dataset-dependent. CMB data alone leave a broad geometric degeneracy, while DESI DR2 BAO pulls the reconstruction toward weak present-day acceleration. In contrast, CMB combined with PP\&SH0ES and BAOtr favors a moderately accelerating expansion and substantially reduces the Hubble tension. The origin of this behavior can be traced to low-redshift distance information: BAOtr and DESI/SDSS prefer different BAO distance ratios at $z\lesssim0.5$, which drives divergent CPL expansion histories. We quantify this mismatch directly at the data level by comparing angular BAO scales, including the common $z=0.510$ point and a conservative local interpolation of BAOtr with no extrapolation. As expected within CPL, where pre-recombination physics is fixed, $r_{\rm d}$ remains nearly unchanged, so shifts in $H_0$ are absorbed by late-time expansion freedom rather than by a change in the sound horizon. Bayesian evidence is likewise contingent on the low-redshift data: it favors CPL mainly when PP\&SH0ES and/or BAOtr are included, is inconclusive for CMB-only and CMB+DESI, and moderately favors $Λ$CDM for CMB+SDSS. These results show that apparent support for CPL and its ability to ease the Hubble tension are not universal, motivating more flexible late-time models and closer scrutiny of BAO systematics.

astro-ph.CO↗
arXiv2026

Entropic Chaplygin-Gas cosmology and late-universe tension diagnostics

Persistent discrepancies between early- and late-Universe measurements have made cosmological tensions a major test of the standard $Λ$CDM model. We investigate whether an entropic generalized Chaplygin-gas cosmology, describing a unified dark sector, can modify the parameter degeneracies associated with these tensions. The model is constrained using Type Ia supernova data from PantheonPlus+SH0ES and DES--Dovekie, DESI BAO measurements, RSD growth data, compressed Planck 2018 distance priors, and a Planck lensing-amplitude prior. We find that the entropic gCg model closely reproduces the $Λ$CDM background expansion while introducing a controlled late-time deformation of the distance--redshift relation. This shifts the preferred $(H_0,Ω_m,S_8)$ region and partially reduces background-driven discrepancies, especially those involving $H_0$. Using \texttt{Tensiometer} to quantify posterior shifts in the common derived parameter space $(H_0,Ω_m,S_8)$, we show that the displacement relative to $Λ$CDM occurs mainly along background-sensitive directions. The model therefore modifies the late-time expansion sector more effectively than the growth sector, leaving residual $S_8$ discrepancies comparatively robust. These results support the possibility that the $H_0$ and $S_8$ tensions arise from distinct physical sectors.

gr-qc↗
arXiv2026

Statistical consistency of sign-switching vacuum energy with cosmological observations

We assess dataset agreement and late-time predictive adequacy in $Λ$CDM and its sign-switching extension, $Λ_{\rm s}$CDM, using a suite of Gaussian and exact non-Gaussian consistency diagnostics. Both models are constrained with cosmic microwave background measurements from Planck, ACT, and SPT, baryon acoustic oscillation data from DESI DR2, and low-redshift Type Ia supernova data from PantheonPlus+SH0ES. We find that commonly used Gaussian tension metrics can significantly overstate inconsistencies when broad, non-Gaussian posteriors are combined with tightly constrained datasets. In contrast, the exact non-Gaussian parameter shift indicates excellent consistency between CMB and BAO observations in both models. The $Λ_{\rm s}$CDM extension modestly improves geometric compatibility at intermediate redshifts, although reductions in parameter-level tension do not necessarily imply improved predictive consistency. These results highlight the importance of exact, non-Gaussian, and predictive diagnostics for robust assessments of cosmological model consistency.

astro-ph.CO↗
arXiv2026

Probing late-time deviations from $Λ$CDM with a quadratic dark energy expansion

We investigate the observational viability of a quadratic dark energy expansion (QDEE) model as a phenomenological extension of the standard $Λ\mathrm{CDM}$ cosmological framework. This approach introduces the additional degrees of freedom that permit mild late-time deviations from a constant dark-energy component while preserving the standard early-Universe behavior. We constrain the model using a comprehensive combination of cosmological datasets, including Planck 2018 cosmic microwave background (CMB) measurements, Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) and South Pole Telescope (SPT-3G) data, Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2), and the Pantheon Plus type Ia supernova compilation. Our results show that the QDEE framework shifts the inferred Hubble constant toward higher values relative to $Λ\mathrm{CDM}$, partially alleviating the tension with local measurements while remaining consistent with early-Universe constraints. Bayesian model comparison indicates strong evidence in favor of this framework over standard $Λ\mathrm{CDM}$ across multiple dataset combinations. Posterior predictive checks further demonstrate that the model yields predictions consistent with the observed data within statistical uncertainties.

astro-ph.CO↗
arXiv2026

Probing dynamical embeddings in a five-dimensional spacetime in light of DESI BAO

We here investigate the observational viability of Nash gravity as an alternative to the standard $Λ$CDM cosmology. Based on Nash's embedding theorem, the model introduces orthogonal perturbations via variations in the extrinsic curvature, generating scalar-type metric perturbations directly from geometry, without the need to introduce additional fields. We confront the model with current observational data, including Cosmic Microwave Background (CMB) measurements from Planck, Baryon Acoustic Oscillations (BAO) from DESI DR2, and recent Type Ia supernova (SN Ia) compilations. Our analysis shows that Nash gravity provides a good fit to the data, yielding a slightly higher value for the Hubble constant, $H_0 = 69.32 \pm 0.72$ km/s/Mpc, compared to the $Λ$CDM model, thus offering a potential alleviation of the $H_0$ tension. Furthermore, the model naturally predicts a suppressed growth of structure, with $S_8 \approx 0.76$ across various joint analyses, potentially alleviating the so-called $S_8$ tension, assuming that this discrepancy is not solely due to systematic effects in other independent measurements. In some cases, Nash gravity achieves a better fit to the data than the $Λ$CDM paradigm at the $2σ$ level.

gr-qc↗
arXiv2025

ECO signatures from the Weyl-induced gravitational waveform injection

We investigate gravitational wave emission from an oscillating star modeled in a static Weyl background using a modulated waveform ansatz. First, we revisit the Weyl metric and obtain a Bessel-type curvature solution with regularity and asymptotic flatness conditions compatible for an astrophysical compact object. Second, we model an oscillating star-like object with a perfect fluid as a source of gravitational radiation. A modified wave equation with curvature-induced redshifts is solved numerically leading to a waveform that produces primary components due to wave trapping. This signal is injected into real LIGO data for GW150914 and compared across detectors allowing the detectability of curvature-induced gravitational waveform in the threshold of LIGO's sensitivity, consistent with an exotic compact object (ECO).

gr-qc↗
arXiv2024

Slow-roll inflation from a geometric scalar-tensor model with self-interacting potentials

We consider slow-roll inflation in the context of a modified Brans-Dicke dilaton gravity. From a two self-interacting potentials $V(ϕ)$, we reproduce a Starobinsky-like potential and, commonly in syperstring models, an exponential tail potential $V(ϕ)\sim(1-e^{α_0ϕ})$, with $α_0$ being a constant coefficient related to the Brans-Dicke parameter $ω$. Using the observational bounds on the spectral index $n_s$ and tensor-to-scalar ratio $r$ imposed by Planck-CMB baseline data and the BICEP2/Keck collaboration with combination with Planck 2018 and the Baryonic Acoustic Oscillations(BAO), we obtain for both models a good agreement with current observations with $n_s = 0.960 - 0.972$ and $r<0.02$. In addition, the resulting large values of $ω$ suggests a possible linkage of the inflationary regime and today's solar system bounds.

gr-qc↗
arXiv2024

Lower tensor-to-scalar ratio as possible signature of modified gravity

This paper simplifies the induced four-dimensional gravitational equations originating from a five-dimensional bulk within the framework of Nash's embeddings, incorporating them into a well-known $μ-Σ$ modified gravity (MG) parametrization. By leveraging data from Planck Public Release 4 (PR4), BICEP/Keck Array 2018, Planck cosmic microwave background lensing, and baryon acoustic oscillation observations, we establish a stringent lower limit for the tensor-to-scalar ratio parameter: $r < 0.0303$ at a confidence level (CL) of 95\%. This finding suggests the presence of extrinsic dynamics influencing standard four-dimensional cosmology. Notably, this limit surpasses those typically obtained through Bayesian analysis using Markov Chain Monte Carlo (MCMC) techniques, which yield $r<0.038$, or through the frequentist profile likelihood method, which yields $r<0.037$ at 95\% CL.

gr-qc↗
arXiv2024

Exploring Modified Gravity: Constraints on the $μ$ and $Σ$ Parametrization with WMAP, ACT, and SPT

The cosmic acceleration problem remains one of the most significant challenges in cosmology. One of the proposed solutions to this problem is the modification of gravity on large scales. In this paper, we explore the well-known $μ$-$Σ$ parametrization scenarios and confront them with observational data, including the cosmic microwave background (CMB) radiation from the Wilkinson Microwave Anisotropy Probe (WMAP), Atacama Cosmology Telescope (ACT), and South Pole Telescope (SPT), as well as large-scale structure data from the Sloan Digital Sky Survey (SDSS: BAO+RSD) and Pantheon Supernovae (SN) catalog. We employ a Bayesian framework to constrain the model parameters and discuss the implications of our results on the viability of modified gravity theories. Our analysis reveals the strengths and limitations of the $μ$-$Σ$ parametrization and provides valuable insights into the nature of gravity on cosmological scales. From the joint analysis of the ACT + WMAP + SDSS + SN, we find $μ_0 -1 = 0.02 \pm 0.19$ and $Σ_0 -1 = 0.021 \pm 0.068$ at 68% CL. In light of the SPT + WMAP + SDSS + SN, we find $μ_0 -1 = 0.07 \pm 0.18$ and $Σ_0 -1 = -0.009^{+0.078}_{-0.11}$ at 68% CL. In all the analyses carried out, we do not find any deviations from the theory of general relativity. Our results represent an observational update on the well-known $μ$-$Σ$ parameterization in view of current CMB data, independent and competitive with the constraints obtained with the Planck data.

astro-ph.CO↗
arXiv2022

Linear Nash-Greene fluctuations on the evolution of $S_8$ and $H_0$ tensions

We present the perturbation equations in an embedded four space-time from the linear Nash-Greene fluctuations of background metric. In the context of a five-dimensional bulk, we show that the cosmological perturbations are only propagated by the gravitational tensorial field equation. In Newtonian conformal gauge, we study the matter density evolution in sub-horizon regime and on how such scale may be affected by the extrinsic curvature. We apply a joint likelihood analysis to the data by means of the Markov Chain Monte Carlo (MCMC) method for parameter estimation using a pack of recent datasets as the Pantheon Supernovae type Ia, the Baryon Acoustic Oscillations (BAO) from DR12 galaxy sample and Dark Energy Survey (DESY$1$). We discuss the tensions on the Hubble constant $H_0$ and the growth amplitude factor $S_8$ of the observations from Planck 2018 Cosmic Microwave Background (CMB) and the local measurements of $H_0$ with Hubble Space Telescope (HST) photometry and Gaia EDR3. As a result, we obtain an alleviation below $\sim 1σ$ in the contours ($S_8$-$Ω_m$) at $68.4\%$ confidence level (CL) when compared with DESY1 data. On the other hand, the $H_0$ tension persists with $\sim 2.6σ$ at $68.4\%$ CL and $1.95σ$ at $95.7\%$ CL, aggravated with the inclusion of BAO data.

gr-qc↗
arXiv2016

Effective perihelion advance and potentials in a conformastatic background with magnetic field

An Exact solution of the Einstein-Maxwell field equations for a conformastatic metric with magnetized sources is study. In this context, effective potential are studied in order to understand the dynamics of the magnetic field in galaxies. We derive the equations of motion for neutral and charged particles in a spacetime background characterized by this class of solutions. In this particular case, we investigate the main physical properties of equatorial circular orbits and related effective potentials. In addition, we obtain an effective analytic expression for the perihelion advance of test particles. Our theoretical predictions are compared with the observational data calibrated with the ephemerides of the planets of the Solar system and the Moon (EPM2011). We show that, in general, the magnetic punctual mass predicts values that are in better agreement with observations than the values predicted in Einstein gravity alone.

gr-qc↗
arXiv2016

Anomalous precession of planets on a Weyl conformastatic solution

In this paper, we investigate the anomalous planets precession in the nearly-newtonian gravitational regime. This limit is obtained from the application of the slow motion condition to the geodesic equations without altering the geodesic deviation equations. Using a non-standard expression for the perihelion advance from the Weyl conformastatic vacuum solution as a model, we can describe the anomaly in planets precession compared with different observational data from Ephemerides of the Planets and the Moon (EPM2008 and EPM2011) and Planetary and Lunar Ephemeris (INPOP10a). As a result, using the Levenberg-Marquardt algorithm and calculating the related Chi-squared statistic, we find that the anomaly is statistical irrelevant in accordance with INPOP10a observations. As a complement to this work, we also do an application to the relativistic precession of giant planets using observational data calibrated with the EPM2011.

gr-qc↗
arXiv2016

Test particles in a magnetized conformastatic spacetime

A class of exact conformastatic solutions of the Einstein-Maxwell field equations is presented in which the gravitational and electromagnetic potentials are completely determined by a harmonic function. We derive the equations of motion for neutral and charged particles in a spacetime background characterized by this class of solutions. As an example, we focus on the analysis of a particular harmonic function, which generates a singularity-free and asymptotically flat spacetime that describes the gravitational field of a punctual mass endowed with a magnetic field. In this particular case, we investigate the main physical properties of equatorial circular orbits. We show that due to the electromagnetic interaction, it is possible to have charged test particles which stay at rest with respect to a static observer located at infinity. Additionally, we obtain an analytic expression for the perihelion advance of test particles and the corresponding explicit value in the case of a punctual magnetic mass. We show that the analytical expressions obtained from our analysis are sufficient for being confronted with observations in order to establish whether such objects can exist in nature.

gr-qc↗
arXiv2015

Motion of test particles in a magnetized conformastatic background

A class of exact conformastatic solutions of the Einstein-Maxwell field equations is presented in which the gravitational and electromagnetic potentials are completely determined by a harmonic function only. The motion of test particles is investigated in the background of a space-time characterized by this class of solutions. We focus on the study of circular stable and unstable orbits obtained by taking account particular harmonic functions defining the gravitational potential. We show that is possible to have repulsive force generated by the charge distribution of the source. As the space-time here considered is singularity free we conclude that this phenomena is not exclusive to the case of naked singularities. Additionally, we obtain an expression for the perihelion advance of the test particles in a general magnetized conformastatic space-time.

gr-qc↗
arXiv2015

Exact Relativistic Magnetized halos around Rotating Disks

The exact relativistic treatment of a rotating disk surrounded by a magnetized material halo is presented. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.

gr-qc↗