arXiv subjects

A. A. Araújo Filho

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

At least 73 records · Page 4Linked to original sources

arXiv2025

Quantum gravity effects on particle creation and evaporation in a non-commutative black hole via mass deformation

In this work, we explore a gravitational non-commutative black hole by gauging the de Sitter SO(4,1) group and employing the Seiberg-Witten map. Specifically, we examine modifications of non-commutativity represented through mass deformation. Initially, we address modifications to Hawking radiation for bosonic particle modes by analyzing the Klein-Gordon equation in curved spacetimes. We compute the Bogoliubov coefficients, showing how $Θ$ introduces a correction to the amplitude associated with particle creation. Additionally, we derive the power spectrum and the Hawking temperature within this framework. We also derive Hawking radiation from a tunneling perspective, leading to expressions for the power spectrum and particle number density. A similar analysis is performed for fermion particles. Remarkably, we obtain an analytical expression for black hole evaporation lifetime and compare our results with recent estimates of non-commutativity in the literature.

gr-qc↗

arXiv2025

Antisymmetric tensor influence on charged black hole lensing phenomena and time delay

In this work, we investigate the gravitational lensing of a charged black hole (spherically symmetric) within the context of Lorentz violation triggered by an antisymmetric tensor field. Our calculations consider two different scenarios: the weak and strong deflection limits. For the weak deflection limit, we employ the Gauss-Bonnet theorem to obtain our results. In the strong deflection limit, we utilize the Tsukamoto methodology, which provides measurable outcomes such as relativistic image positions and magnifications. Applying the latter methodology, we analyze the gravitational lensing by Sagittarius $A^{*}$ and derive the related observables, which are expressed as functions of the Lorentz violation parameter. Finally, the time delay is addressed as well.

gr-qc↗

arXiv2025

Geodesics, accretion disk, gravitational lensing, time delay, and effects on neutrinos induced by a non-commutative black hole

This paper explores gravitational phenomena associated with a non-commutative black hole. Geodesic equations are derived, and a thin accretion disk is analyzed to model the black hole shadow image, considering an optically thin, radiating, and infalling gas. Retrolensing effects are examined to trace photon emission configurations, while gravitational lensing is investigated through weak and strong deflection limits, with lensing equations and observables applied to Sagittarius A*. The study also includes calculations of time delay, energy deposition rate from neutrino annihilation, phase and probability of neutrino oscillation, and neutrino gravitational lensing.

gr-qc↗

arXiv2025

How does non-metricity affect particle creation and evaporation in bumblebee gravity?

In this work, we analyze the impact of non-metricity on particle creation and the evaporation process of black holes within the framework of bumblebee gravity. In general lines, we compare black holes in the metric formalism [1] and the metric-affine approach [2]. Initially, we focus on bosonic particle modes to investigate Hawking radiation. Using the Klein-Gordon equation, we compute the Bogoliubov coefficients and derive the Hawking temperature. Subsequently, we examine Hawking radiation as a tunneling process, resolving divergent integrals through the residue method. The analysis is then extended to fermionic particle modes, also within the tunneling framework. Particle creation densities are calculated for both bosonic and fermionic cases. Additionally, greybody bounds are estimated for bosonic and fermionic particles. Furthermore, we explore the evaporation process, considering the final state of the black holes and we also investigate the correlation between the greybody factors and the quasinormal modes. Finally, constraints on the Lorentz-violating parameters $\ell$ (for the metric case) and $X$ (for the metric-affine case) are established using recent astrophysical data on black hole lifetimes. In a general panorama, non-metricity (except for the tensor perturbations) in bumblebee gravity raises particle density for bosons while reducing it for fermions, increases greybody factors (for both bosons and fermions), amplifies the emission rate, and accelerates the evaporation process.

gr-qc↗

arXiv2025

Analysis of a nonlinear electromagnetic generalization of the Reissner-Nordström black hole

In this work, we investigate the gravitational signatures of a nonlinear electromagnetic extension of the Reissner-Nordström solution. We conduct an analysis of light propagation, focusing on the photon sphere, shadow formation, and geodesic trajectories in this spacetime. The constraints on the parameter $ξ$, which characterizes the nonlinear extension of the Reissner-Nordström black hole, are derived from observational data provided by the Event Horizon Telescope (EHT). The time delay effects are also considered. In the thermodynamic analysis, we examine the Hawking temperature, entropy, heat capacity, and the emission of Hawking radiation via the tunneling process. The remnant mass and evaporation time of the black hole at its final stage are estimated. In addition, we compute the quasinormal modes using the WKB approximation, taking into account the characteristic oscillations of the system under scalar, vector, and tensor perturbations. Additionally, the time-domain solution is analyzed for all these perturbations to examine their evolution over time.

gr-qc↗

arXiv2025

Particle creation and evaporation in Kalb-Ramond gravity

In this work, we examine particle creation and the evaporation process in the context of Kalb-Ramond gravity. Specifically, we build upon two existing solutions from the literature [1] (Model I) and [2] (Model II), both addressing a static, spherically symmetric configuration. For this study, we focus on the scenario in which the cosmological constant vanishes. The analysis begins by examining bosonic particles to investigate Hawking radiation. Using the Klein-Gordon equation, the Bogoliubov coefficients are derived, highlighting the role of the parameter $\ell$, which governs Lorentz symmetry breaking, in introducing corrections to the amplitude of particle production. This forms the basis for calculating the Hawking temperature. The study further explores Hawking radiation through the tunneling mechanism, where divergent integrals are solved using the residue method. The particle creation density is also computed for fermionic particle modes. Additionally, greybody bounds are evaluated for bosons and fermions as well. Finally, we analyze the deviation of our results from those predicted by general relativity. In a general panorama, Model I exhibits the highest particle creation densities and the fastest evaporation process, whereas Model II shows the largest greybody factor intensities.

gr-qc↗

arXiv2025

Absorption, Scattering, Geodesics, Shadows and Lensing Phenomena of Black Holes in Effective Quantum Gravity

In this work, we investigate the signatures of black holes within an effective quantum gravity framework recently proposed in the literature [1] . We begin by outlining the general setup, highlighting the two distinct models under consideration. This includes a discussion of their general properties, interpretations, and the structure of the event and inner horizons. We then examine the behavior of light in this context, analyzing geodesics, the photon sphere, and shadow formation. To validate our results, we estimate lower bounds for the shadow radius based on observational data from the Event Horizon Telescope (EHT). Subsequently, we derive the partial radial wave equation for scalar perturbations, enabling us to study the absorption cross section in both low and high frequency regimes. Additionally, we evaluate the greybody factors and provide bounds for both bosonic and fermionic fields. Finally, we present a detailed analysis of gravitational lensing in both the weak and strong deflection limits. For the weak deflection regime, the Gauss Bonnet theorem is employed, while for the strong deflection limit, the Tsukamoto approach is utilized.

gr-qc↗

arXiv2025

The impact of an antisymmetric tensor on charged black holes: evaporation process, geodesics, deflection angle, scattering effects and quasinormal modes

In this paper, we investigate the influence of anti-symmetric tensor effects, which trigger the Lorentz symmetry breaking, on charged spherically symmetric black holes. Initially, we address an overview of the model, laying the groundwork for deriving solutions to black holes. With this, we analyze the horizons, critical orbits, and geodesics. We compute quasinormal modes and the time-domain solution with a particular emphasis on vectorial perturbations. In addition, we derive the Hawking temperature to perform the calculation of the remnant mass. Additionally, we estimate the lifetime of the black holes until they reach their final stage after the evaporation process. Finally, we explore the emission rate, the deflection angle and, we investigate the correlation between quasinormal modes and shadows.

gr-qc↗

arXiv2025

Remarks on a nonlinear electromagnetic extension in AdS Reissner-Nordström spacetime

We explore the gravitational properties of a nonlinear electromagnetic extension of an AdS Reissner-Nordström black hole. Our study begins with an analysis of the metric function and horizon structure, followed by calculations of the Ricci and Kretschmann scalars and an evaluation of the non-vanishing Christoffel symbols. These calculations allow us to examine geodesics and their influence on the photon sphere, and shadow formation. In the thermodynamic framework, we evaluate essential quantities, including the Hawking temperature, entropy, heat capacity, Gibbs free energy, and Hawking radiation emission. We further investigate black hole evaporation by estimating the evaporation timescale as the black hole approaches its final state. Additionally, quasinormal modes for scalar and vector perturbations are computed using the WKB approximation to characterize oscillatory behavior of the system. Finally, a time-domain analysis is provided in order to examine the evolution of these perturbations.

gr-qc↗

arXiv2025

Thermodynamical properties of a deformed Schwarzschild black hole via Dunkl generalization

In this paper, we construct a deformed Schwarzschild black hole from the de Sitter gauge theory of gravity within Dunkl generalization and we determine the metric coefficients versus Dunkl parameter and parity operators. Since the spacetime coordinates are not affected by the group transformations, only fields are allowed to change under the action of the symmetry group. A particular ansatz for the gauge fields is chosen and the components of the strength tensor are computed as well. Additionally, we analyze the modifications on the thermodynamic properties to a spherically symmetric black hole due to Dunkl parameters for even and odd parities. Finally, we verify a novel remark highlighted from heat capacity: the appearance of a phase transition when the odd parity is taken into account.

gr-qc↗

arXiv2025

Modified particle dynamics and thermodynamics in a traversable wormhole in bumblebee gravity

In this work, we analyze various phenomena influenced by the gravitational field in a bumblebee gravity solution, with a particular emphasis on a traversable wormhole for massless particle modes. Specifically, we calculate the index of refraction, group velocity, time delay, modified distances, and interparticle potential, demonstrating the possibility of photon-photon interactions due to the wormhole geometry. For the latter aspect, we also extend the analysis to massive particle modes, resulting in a ``combination'' of modified Yukawa- and Couloumb-like potentials. These calculations are shown to be dependent on the wormhole's parameters, particularly the wormhole throat. In addition to these analyses, the Hawking temperature is derived using the trapping horizon method, yielding negative values. Furthermore, we derive the thermodynamic properties of photon-like modes by incorporating the modified dispersion relation arising from the wormhole geometry, focusing on non-interacting particle modes. Remarkably, all calculations are conducted in a fully analytical framework.

gr-qc↗

arXiv2025

Properties of an axisymmetric Lorentzian non-commutative black hole

In this work, we start by examining a spherically symmetric black hole within the framework of non-commutative geometry and apply a modified Newman-Janis method to obtain a new rotating solution. We then investigate its consequences, focusing on the horizon structure, ergospheres, and the black hole's angular velocity. Following this, a detailed thermodynamic analysis is performed, covering surface gravity, Hawking temperature, entropy, and heat capacity. We also study geodesic motion, with particular emphasis on null geodesics and their associated radial accelerations. Additionally, the photon sphere and the resulting black hole shadows are explored. Finally, we compute the quasinormal modes for scalar perturbations using the 6th-order WKB approximation.

gr-qc↗

arXiv2024

Strain effects on the electronic properties of a graphene wormhole

In this work, we explore the strain and curvature effects on the electronic properties of a curved graphene structure, called the graphene wormhole. The electron dynamics is described by a massless Dirac fermion containing position--dependent Fermi velocity. In addition, the strain produces a pseudo--magnetic vector potential to the geometric coupling. For an isotropic strain tensor, the decoupled components of the spinor field exhibit a supersymmetric (SUSY) potential, depending on the centrifugal term and the external magnetic field only. In the absence of a external magnetic field, the strain yields to an exponential damped amplitude, whereas the curvature leads to a power--law damping of the wave function. The spin--curvature coupling breaks the chiral symmetry between the upper and the lower spinor component, which leads to the increasing of the wave function on either upper or lower region of the wormhole, i.e., depending on the spin number. By adding an uniform magnetic field, the effective potential exhibits an asymptotic quadratic profile and a spin--curvature barrier near the throat. As a result, the bound states (Landau levels) are confined around the wormhole throat showing an asymmetric and spin--dependent profile.

cond-mat.mes-hall↗

arXiv2024

Effects of non-commutative geometry on black hole properties

In this study, we investigate the signatures of a non-commutative black hole solution. Initially, we calculate the thermodynamic properties of the system, including entropy, heat capacity, and Hawking radiation. For the latter quantity, we employ two distinct methods: surface gravity and the topological approach. Additionally, we examine the emission rate and remnant mass within this context. Remarkably, the lifetime of the black hole, after reaching its final state due to the evaporation process, is expressed analytically up to a grey-body factor. We estimate the lifetime for specific initial and final mass configurations. Also, we analyze the tensorial quasinormal modes using the 6th-order WKB method. Finally, we study the deflection angle, i.e., gravitational lensing, in both the weak and strong deflection limits.

gr-qc↗

arXiv2024

Thermal, topological, and scattering effects of an AdS charged black hole with an antisymmetric tensor background

In this study, we explore a spherically symmetric charged black hole with a cosmological constant under the influence of a Kalb--Ramond field background. We compute the photon sphere and shadow radii, validating our findings using observational data from the Event Horizon Telescope (EHT), with a particular emphasis on the shadow images of Sagittarius $A^{*}$. Furthermore, we investigate the \textit{greybody} factors, emission rate, and partial absorption cross section. It is shown that the Lorentz-violating parameter $\bar{l}$ has an important effect on the absorption cross section. Our analysis also includes an examination of the topological charge, temperature-dependent topology, and generalized free energy. In particular, we regard the AdS charged black hole with an antisymmetric tensor background as a topological defect in the thermodynamic space, then the system has the same topological classification to the charged RN-AdS black hole.

gr-qc↗

arXiv2024

Fermions with Electric Dipole Moment in curved spacetime

This paper explores the relativistic behavior of spin--half particles possessing an Electric Dipole Moment (EDM) in a curved spacetime background induced by a spiral dislocation. A thorough review of the mathematical formulation of the Dirac spinor in the framework of quantum field theory sets the foundation for our investigation. By deriving the action that governs the interaction between the spinor field, the background spacetime, and an external electric field, we establish a framework to study the dynamics of the system. Solving the resulting wave equation reveals a set of coupled equations for the radial components of the Dirac spinor, which give rise to a modified energy spectrum attributed to the EDM. To validate our findings, we apply them to the geometric phase and thermodynamics.

gr-qc↗

arXiv2024

Shadows, greybody factors, emission rate, topological charge, and phase transitions for a charged black hole with a Kalb-Ramond field background

In this work, we investigate a spherically symmetric charged black hole in the presence of a Kalb--Ramond field background. We calculate the photon sphere and shadow radii and, corroborating our results, we constrain them from observational data from the Event Horizon Telescope (EHT), particularly focusing on the shadow images of Sagittarius $A^{*}$. Additionally, we analyze the greybody factors, emission rate, and partial absorption cross section. We also examine the topological charge and its application to the deflection angle. Finally, we conduct the analysis of the heat capacity and phase transitions.

gr-qc↗

arXiv2024

Scattering effects of bumblebee gravity in metric affine formalism

In this work, we explore a Schwarzschild-like black hole within the framework of metric--affine bumblebee gravity. First, we investigate the behavior of the Kretschmann scalar and singularities in this modified gravity approach. Next, we introduce a newly defined time coordinate related to a stationary asymptotically flat spacetime. We also analyze the scattering effects and numerically calculate and comprehensively examine the partial and total absorption cross sections. At the high--frequency approximation, we find that the absorption cross section tends to the geodesic capture cross section. The continued fraction method is applied to investigate the quasinormal modes, and we explore the deviations of both the real and imaginary terms of the quasinormal modes from the Schwarzschild case in detail. We verify the relation between the shadow radius and the real part of the quasinormal frequencies at the eikonal limit within this modified gravity framework. Finally, we examine the energy emission rate.

gr-qc↗