arXiv subjects

A. A. Araújo Filho

Publications and source records attributed to A. A. Araújo Filho.

At least 37 records · Page 2Linked to original sources

arXiv2026

Regular Black Holes in General Relativity from Nonlinear Electrodynamics with de Sitter Cores

We present new regular black hole solutions in general relativity (GR) within a static, spherically symmetric framework governed by a variable equation of state, following the approach of [Class. Quant. Grav. 42, 025024 (2025)]. The matter supporting these geometries is identified as a purely magnetic monopole configuration of the Maxwell-Faraday tensor in the context of nonlinear electrodynamics (NLED). We explicitly reconstruct the corresponding NLED Lagrangian and analyze the asymptotic and central behaviors of the solutions. The geometric structure is examined through the metric functions, the regularity of the Kretschmann scalar, and the profiles of energy density and pressures, including a discussion of the resulting energy conditions. Using Event Horizon Telescope observations of Sgr A$^*$, we constrain the model parameters by comparing the predicted size of the central dark region with the inferred observational images, taking into account the effective geometry experienced by photons in the presence of NLED. Finally, we investigate the dynamical stability of these configurations under scalar perturbations by computing the quasinormal mode spectrum and performing a time-domain analysis.

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arXiv2026

Lorentz-violating modifications to particle dynamics, thermodynamics and vacuum energy in bumblebee gravity

We investigate how spontaneous Lorentz symmetry breaking in bumblebee gravity modifies particle dynamics, thermodynamics, and vacuum energy around a static black hole background. Starting from the optical-mechanical correspondence, we derive a modified dispersion relation that encodes the influence of the Lorentz-violating parameter $λ$ on the propagation of massive and massless modes. We analyze the resulting optical properties, including the effective refractive index, group velocity, and energy-dependent time delay, and show how the non-asymptotically flat geometry reshapes signal propagation. From the same dispersion relation, we construct the interparticle potential for massive and massless excitations and evaluate the electron scattering cross section within the Born approximation, identifying characteristic Lorentz-violating corrections. We then develop a statistical-ensemble description based on the deformed energy-momentum relation and obtain analytic expressions for the thermodynamic observables of a massless bosonic gas. The pressure, mean energy, entropy, and heat capacity are examined in three representative regimes -- extremely close to the horizon, near the photon sphere, and in the asymptotic region -- where Lorentz violation systematically increase the magnitude of these quantities and leads to finite asymptotic plateaus. Finally, we analyze the vacuum state in the curved background and compute the regularized Casimir energy at zero and finite temperature.

gr-qc↗

arXiv2026

Light propagation and gravitational lensing effects in charged Kalb-Ramond spacetime in nonlinear electrodynamics

In this work, we theoretically investigate the deflection of light for strong- and weak-field regimes in the background of an electrically charged BH described in Kalb-Ramond gravity, which introduces the Lorentz symmetry violation parameter $l$, as well as the control of the degree of nonlinearity incorporated by electrodynamics through the parameter $γ$. We analytically constructed the expansion coefficients in both limits and used them as a basis to investigate gravitational lensing effects through observables, taking into account the variation of the parameters involved in the model, both for the canonical field and the phantom case.

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arXiv2026

Gravitational Wave Signatures from Periodic Orbits around a Non--commutative Schwarzschild Black Hole

In this work, we investigate massive particle motion and the gravitational wave emission generated by periodic trajectories around a non--commutative \textit{Schwarzschild} black hole sourced by a Lorentzian matter distribution. We analyze the effective potential, the marginally bound orbit, and the innermost stable circular orbit, showing that non--commutative corrections shift these characteristic orbits toward smaller radii and reduce their corresponding angular momenta. The allowed region in the $(E, L)$ plane is also displaced toward lower values, favoring more tightly bound configurations. Periodic trajectories are classified through the rational parameter $q$, which relates the radial and azimuthal frequencies. For a fixed orbital topology, increasing the non--commutative parameter lowers the energy required to produce the orbit and results in more compact zoom--whirl configurations. Small deviations from the periodic energies are also shown to generate precessional drift. From the periastron advance of the S2 star around Sgr~A$^*$, we obtain the preliminary bound $Θ/M^{2}<0.014$. Finally, using the adiabatic and numerical kludge approximations, we compute the gravitational wave polarizations and find phase shifts and an overall enhancement of the amplitude.

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arXiv2026

Non-metricity effects on electron scattering in bumblebee gravity

We investigate non-metricity effects on electron scattering in metric-affine bumblebee gravity, where spontaneous Lorentz symmetry breaking is induced by a vector field acquiring a nonzero vacuum expectation value. Treating the affine connection as an independent variable and integrating it out leads to an effective description in which non-metricity modifies the dispersion relation of the bumblebee modes. From the full momentum-space propagator, we determine the pole structure that governs the interaction and construct the corresponding static Green function and interparticle potential. For a purely timelike background, the dispersion relation remains isotropic and produces a Coulomb potential with a uniformly rescaled effective coupling; consequently, the scattering amplitude preserves the Rutherford angular dependence, with the Lorentz-violating parameter entering only as an overall multiplicative factor. In contrast, a spacelike background induces anisotropy in the dispersion relation, leading to an orientation-dependent potential characterized by a quadrupolar modulation. This anisotropic structure propagates to the differential and integrated cross sections, introducing directional dependence while preserving the long-range character of the interaction. Finally, we consider phenomenological constraints from atomic physics. Hydrogen spectroscopy constrains the isotropic sector associated with the timelike configuration, whereas searches for anisotropies provide stronger limits on the quadrupolar contribution governed by $ξb^{2}$.

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arXiv2026

Signatures of a de Sitter-core black hole in ringing, transmission and optical appearance

We investigate a static, asymptotically flat black hole whose central region approaches a de Sitter vacuum. The geometry is controlled by the ADM mass $M_0$ and a core scale $R$, and is generated by an exponentially decaying anisotropic source. After clarifying the stress tensor and the horizon structure, we study scalar-field perturbations, greybody transmission, Hawking emission and the optical image produced by an optically thin infalling flow. The horizon analysis shows that two horizons exist below the critical value $R/M_0\simeq0.7768$, where they merge into an extremal configuration. Increasing the core scale lowers the peak of the scalar effective potential and shifts the quasinormal spectrum away from the Schwarzschild value, with the largest fractional deviations occurring for low multipoles and higher overtones within the WKB domain of validity. The greybody bound indicates stronger filtering as the core becomes more extended, while the QNM--greybody correspondence gives a complementary estimate of the transmission probability in the eikonal regime. The Hawking temperature decreases as the extremal configuration is approached, suppressing the emission rate and shifting its maximum to lower frequencies. For a simple optically thin infalling flow, ray tracing shows a small decrease in the apparent shadow scale and in the peak intensity as the core scale is increased.

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arXiv2026

Optical Phenomena in a Non-Commutative Kalb-Ramond Black Hole Spacetime

This work investigates additional gravitational features of a newly proposed black hole spacetime within Kalb-Ramond gravity, incorporating non-commutative corrections arising from a gauge-theoretic approach recently introduced in the literature [arXiv:2507.17390]. Accordingly, null geodesics are solved numerically to trace photon paths; the photon sphere and shadow are determined. From Event Horizon Telescope (EHT) measurements of $Sgr A^{*}$, constraints on the parameters $Θ$ (which encapsulates the non-commutativity) and $\ell$ (the Lorentz-violating parameter) are established. To examine the stability of critical orbits and the deflection angle (gravitational lensing) in the weak field scenario, we compute the Gaussian curvature in order to use the Gauss-Bonnet theorem. Moreover, the deflection angle has been calculated as well in the strong deflection limit. Furthermore, Lensing observables are estimated using EHT data for $Sgr A^{*}$ and $M87$. Topological features such as the topological photon sphere are also explored.

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arXiv2026

Perturbative dynamics and relativistic effects of a dyonic Kalb-Ramond black hole

We investigate perturbative dynamics, tidal effects, and relativistic frequency shifts in a dyonic Kalb-Ramond black hole generated by a Lorentz-violating antisymmetric tensor background. The geometry is controlled by the mass $M$, the electric charge $Q$, the magnetic charge $p$, and the Lorentz-violating parameter $\ell$, with the dyonic sector entering through the effective combination $P_{\ell}^{2}=Q^{2}/(1-\ell)^{2}+p^{2}/(1-2\ell)$. First, we analyze the gravitational Doppler effect for radial signal exchange between freely falling and static observers, showing how the dyonic charges weaken the redshift by shifting the frequency ratio toward unity. We then compute the radial and angular tidal forces in a freely falling frame and determine the characteristic radii at which the usual stretching and compression patterns are reversed. The gravitational time delay is also evaluated for null trajectories, showing that the electric and magnetic sectors reduce the delay relative to the reference configuration. In the perturbative sector, we derive the scalar, vector, tensor, and spinor effective potentials and compute the corresponding quasinormal frequencies through the sixth-order WKB method. The numerical spectra indicate that the Lorentz-violating parameter gives the dominant correction, increasing the oscillation frequencies and modifying the damping rates, while the dyonic charges produce milder shifts. Finally, the time-domain profiles confirm the presence of damped quasinormal ringing followed by late-time power-law tails.

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arXiv2026

Light propagation and quasinormal modes of a topologically charged Schwarzschild-Klinkhamer wormhole

In this work, we present a theoretical analysis of null geodesics, critical photon orbits, and shadow formation associated with a wormhole generated by a geometric defect. The propagation of light in this spacetime is examined through the deflection angle in both weak- and strong-field regimes. Analytical expansions are derived in each regime and employed to characterize gravitational lensing observables. By varying the global monopole charge, we evaluate its impact on these observables and determine parameter ranges that may be accessible to current or future observational probes. Finally, we calculate the quasinormal modes as well as the time-domain solution for scalar perturbations as well.

gr-qc↗

arXiv2026

Propagation effects of Lorentz violation in gravitational waves

We investigate the propagation of gravitational waves in the presence of Lorentz- and diffeomorphism-violating operators within the linearized gravitational sector of the Standard Model Extension. Focusing on isotropic contributions, we analyze the combined effects of the CPT-even dimension-four coefficient $\mathring{k}^{(4)}_{(I)}$ and the CPT-odd dimension-five coefficient $\mathring{k}^{(5)}_{(V)}$ on tensorial gravitational radiation. The modified dispersion relation induces both a rescaling of the propagation speed and helicity-dependent corrections, leading to birefringence and polarization mixing without introducing additional propagating degrees of freedom. We derive the retarded Green function associated with the modified wave operator and obtain explicit expressions for the gravitational waveform generated by matter sources. As an application, we examine a binary black hole system and show how Lorentz violation alters the observed strain through shifted retarded times, amplitude rescaling, and higher derivative corrections to the quadrupole formula. Using GW170817/GRB 170817A, published GWTC-3 propagation tests, and conservative polarization consistency arguments, we translate existing observational constraints into bounds on $\mathring{k}^{(4)}_{(I)}$ and $\mathring{k}^{(5)}_{(V)}$.

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arXiv2026

Gravitational waves in metric-affine bumblebee gravity

We study the propagation and emission of gravitational waves in the metric-affine formulation of the bumblebee model, where spontaneous Lorentz symmetry breaking arises from a vector field acquiring a nonvanishing vacuum expectation value. Working in the geometric-optics limit of the linearized theory, we derive the modified dispersion relation governing the graviton modes and show that it depends on the orientation of the wave vector relative to the background vector. The polarization sector is examined for timelike and spacelike configurations of the Lorentz-violating vacuum. In both cases only two independent tensor modes propagate, although their propagation properties and tensor structure depend on the orientation of the background field. We then construct the retarded Green function associated with the modified wave operator and determine the radiation-zone produced by localized sources. In the timelike configuration the Lorentz-violating effects appear through a modified propagation speed and an overall amplitude renormalization, leading to a shifted retarded time while preserving the quadrupole structure of the waveform. In contrast, the spacelike sector introduces anisotropic corrections to the quadrupole amplitude together with an additional contribution proportional to the third time derivative of the quadrupole moment. As an astrophysical application, the gravitational radiation emitted by a circular binary black hole system is evaluated, allowing observational constraints on the Lorentz-violating combination $ξb^{2}$ to be estimated using multimessenger bounds from GW170817/GRB~170817A and waveform consistency requirements from gravitational wave observations.

gr-qc↗

arXiv2026

The role of non-metricity on neutrino behavior in bumblebee gravity

Within the context of bumblebee gravity, this work explores how non-metricity alters the behavior and propagation of neutrinos. Our analysis is based on the black hole configuration introduced in Ref. [1], focusing on how the spacetime deformation affects some neutrino-related processes. Three primary aspects are fundamentally taken into account: the modification in the energy deposition rate stemming from neutrino-antineutrino annihilation, the alterations in the oscillation phase caused by the background geometry, and the role of lensing effects on the transition probabilities among neutrino flavors. Complementing the analytical approach, numerical evaluations of oscillation probabilities are performed within a two-flavor scenario, accounting for both inverted and normal mass ordering configurations.

gr-qc↗

arXiv2026

The Flight of the Bumblebee in a Non-Commutative Geometry: A New Black Hole Solution

This paper investigates a new black hole solution within the framework of bumblebee gravity, incorporating non-commutative corrections parameterized by $Θ$ and implemented through the Moyal twist $\partial_r \wedge \partial_θ$. Notably, the event horizon remains unaffected by $Θ$, while the surface gravity becomes ill-defined, in agreement with the behavior previously reported for the non-commutative Schwarzschild black hole [1]. The propagation of light is examined by analyzing null geodesics, identifying critical orbits, and determining the resulting black hole shadow. To complement these analyses, we explore gravitational lensing by evaluating the deflection angle in both the weak- and strong-field regimes. Using these results, constraints are derived for the lensing observables by comparing with the Event Horizon Telescope data for $Sgr A^{*}$ and $M87^{*}$. Finally, we close the analysis by deriving additional constraints from standard Solar System experiments, including Mercury's orbital precession, gravitational light bending, and time-delay measurements.

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arXiv2026

Particle production, absorption, scattering, and geodesics in a Schwarzschild-Hernquist black hole

We investigate quantum and classical signatures of a Schwarzschild black hole embedded in a Hernquist dark matter halo. Starting from the exact spherically symmetric solution describing this composite system, we analyze particle production for both bosonic and fermionic fields using semiclassical techniques. Hawking radiation is derived through Bogoliubov transformations and independently via the tunneling method with energy conservation, allowing us to identify the effective temperature, emission spectrum, and the role of dark matter parameters in suppressing particle creation. The evaporation process is examined in the high-frequency regime, leading to modified evaporation times and emission rates relative to the vacuum Schwarzschild case. We further study absorption and scattering of massless scalar waves employing a partial-wave analysis, computing phase shifts, partial and total cross sections, and assessing the impact of the Hernquist scale radius and density on these observables. Finally, null and timelike geodesics are explored to characterize light propagation and particle motion in the presence of the dark matter halo.

gr-qc↗

arXiv2026

Spin effects on particle creation and evaporation in $f(R,T)$ gravity

In this work, we study how the spin of particle modes influences particle creation, greybody factors, absorption, and evaporation of a black hole within the framework of modified electrodynamics in $f(R,T)$ gravity, recently proposed in Ref. [1]. All spin sectors -- scalar, vector, tensor, and spinorial -- are analyzed to obtain the corresponding features. For particle creation, we consider massless bosonic and fermionic perturbations to determine the respective particle densities. Analytical expressions for the greybody factors are derived, with suitable approximations for the tensor and spinorial cases. The absorption cross section is computed numerically, and using the Stefan-Boltzmann law, we estimate the black hole evaporation lifetime. The associated energy and particle emission rates are also discussed, along with the correspondence between quasinormal modes and greybody factors.

gr-qc↗

arXiv2026

Gravitational aspects of a new bumblebee black hole

In this paper, we examine the physical consequences of a recently introduced black hole solution in bumblebee gravity [1]. The geometry is first presented and then reformulated through suitable coordinate adjustments, which make its global conical character evident. We then study the propagation of particles by solving the geodesic equations for null and timelike trajectories. The associated critical orbits (or photon spheres) are obtained, and shadow radius are computed and compared with other Lorentz-violating configurations in bumblebee and Kalb-Ramond models, including their charged and cosmological extensions. Massive particle motion is analyzed separately, followed by the construction of the effective potentials for scalar, vector, tensor, and spinor perturbations. These potentials allow the calculations of quasinormal frequencies and the corresponding time-domain evolution. Gravitational lensing phenomena are investigated in the weak and strong deflection regimes, and the light-travel time delay is also evaluated. The study concludes with bounds on the Lorentz-violating parameter based on classical Solar System experiments.

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arXiv2026

Electromagnetic dynamics and geometric transport in spin-nondegenerate SME particles

We investigate the electromagnetic dynamics of spin-nondegenerate classical particle models arising from Lorentz-violating sectors of the Standard-Model Extension, focusing on the $b_μ$ background. Starting from the type-2 relativistic Lagrangian, we introduce minimal electromagnetic coupling and derive the exact Hamiltonian dynamics associated with each sector in terms of the gauge-covariant kinetic momentum. The modified dispersion relation leads to a sector-dependent relation between velocity and momentum, which directly affects the response to external fields. In the presence of a uniform magnetic field, we show that the two sectors exhibit distinct cyclotron frequencies and radii, implying that even constant fields dynamically resolve the underlying structure of the theory. In the nonrelativistic regime, the Lorentz-violating background induces a sector-dependent modification of the transverse inertial response, which can be interpreted as an effective anisotropic mass. After projection onto a single sector, the reduced dynamics acquires a noncanonical symplectic structure. The equations of motion can be written in semiclassical form with an effective momentum space curvature $Ω_{\pm}$, leading to anomalous velocity terms and a modified phase-space measure. As a consequence, a purely electric field generates opposite transverse drifts proportional to $q\,\mathbf{E} \times Ω_{\pm}$, producing a Hall-like current without requiring a magnetic field.

physics.gen-ph↗

arXiv2026

Gravitational waves in a minimal gravitational SME

In this work, we investigate the generation and propagation of gravitational waves within a minimal gravitational SME (Standard Model Extension). Starting from the modified graviton dispersion relation derived in the linearized gravity sector, we analyze the polarization properties of gravitational waves in the transverse-traceless tensor sector. We then construct the retarded Green function associated with the Lorentz-violating wave operator, explicitly verifying the causal structure of the theory and identifying the modified propagation speeds of the tensorial modes. In addition, we study the source-induced emission of gravitational waves from a binary black-hole system. We show that the gravitational waveform preserves the standard quadrupolar amplitude and polarization structure, while Lorentz-violating effects enter exclusively through a modification of the retarded time. As a result, the spatial components of the metric perturbation $h_{ij}(t,r)$ acquire a phase shift determined by the SME coefficients. Finally, we estimate phenomenological bounds to the model under consideration.

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