arXiv subjects

A. A. Araújo Filho

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

At least 55 records · Page 3Linked to original sources

arXiv2026

Casimir Effect for a Massive Scalar Field in Lorentz-Violating Aether Compactification

This work investigates the influence of Lorentz symmetry breaking, introduced by an aether-like field $α_ϕ$, on the Casimir effect within a five-dimensional flat spacetime. By considering a quasiperiodic condition regulated by the parameter $β$ and an extra dimension compactified at scale $b$, we derive closed-form expressions for the Casimir energy and the resulting force between two parallel plates under Neumann boundary conditions. Our results demonstrate that $β$ acts as a crucial control parameter, enabling a continuous transition between attractive and repulsive regimes, with a characteristic symmetry around $β= 0.5$. We show that the Lorentz-violating parameter $α_ϕ$ functions as an enhancement factor, significantly amplifying the vacuum interaction, while the geometric ratio $a/b$ proves decisive for system stabilization. Specifically, we find that the high-compactification regime leads to a plateau in the Casimir force, effectively stabilizing the interaction. Furthermore, we analyze the mass spectrum of the field, recovering standard geometric forms in the massless limit and demonstrating that while light fields ($M \ll 1$) exhibit subtle quadratic corrections, heavy fields ($M \gg 1$) lead to an exponential suppression of the Casimir effect. The interplay between Lorentz violation and extra-dimensional compactification provides a rich mechanism with potential applications in the modulation of vacuum-induced interactions at micro and nano scales.

hep-th↗

arXiv2026

Casimir phenomena in bumblebee gravity

In this work, we analyze the Casimir effect associated with a massive, non-minimally coupled scalar field in static, spherically symmetric black hole spacetimes arising in bumblebee gravity. Three distinct solutions are considered, corresponding to different vacuum expectation value configurations of the Lorentz-violating vector field, including metric and \textit{metric-affine} scenarios. Finite-size effects are implemented through the Thermo Field Dynamics formalism by compactifying the radial direction, allowing the construction of renormalized vacuum expectation values of the energy-momentum tensor. Closed-form expressions for the Casimir energy and pressure are obtained in the massless limit as functions of the radial position of a spherical capacitor and the plate separation. Both observables depend explicitly on the bumblebee parameters and on the location of the apparatus relative to the horizon $R_0=2M$. In the weak-field regime, $r \gg R_0$, the standard flat-space behavior $E \propto -1/d^4$ is recovered. As $r \to R_0$, the Casimir energy vanishes while the radial pressure diverges. Inside the black hole, the interaction may alternate between attractive and repulsive regimes depending on the plate separation and on the Lorentz-violating couplings. A domain-dependent hierarchy among the three configurations emerges, with \textit{metric-affine} effects amplifying the interior vacuum energy, while configurations with simultaneous temporal and radial deformations dominate in the exterior region. Although all geometries share the same asymptotic Schwarzschild structure, their quantitative deviations become increasingly pronounced as the Lorentz-violating parameters grow.

gr-qc↗

arXiv2026

Quantum features of a non-commutative Schwarzschild black hole

This work aims to present the quantum aspects of a non-commutative gauge gravity formulation of a Schwarzschild-like black hole constructed via the Moyal twist $\partial_t \wedge \partial_θ$. Particle creation is estimated for bosonic and fermionic fields using the quantum tunneling method, with divergent integrals treated through the residue prescription. Since the surface gravity is well defined for this configuration, the corresponding emission rates and evaporation lifetimes are also computed. In addition, previously reported results in the literature on gauge gravity Schwarzschild black holes are revisited. Finally, we infer constraints on the non-commutative parameter $Θ$ from solar-system tests.

gr-qc↗

arXiv2025

Entanglement, equivalence principle, and HBAR entropy, in a new bumblebee black hole

We investigate quantum information and thermodynamic properties of a new bumblebee black hole arising from spontaneous Lorentz symmetry breaking by analyzing near-horizon physics through complementary quantum probes. We study the degradation of quantum entanglement for field modes shared by inertial and accelerated observers in spacelike and lightlike Lorentz-violating vacua that generate identical spacetime metrics. Using the near-horizon Rindler correspondence, we derive analytic expressions for the logarithmic negativity and mutual information and examine their dependence on detector position, frequency, and Lorentz-violation parameters. Despite sharing the same metric, the two Lorentz-violating vacua become distinguishable near the horizon, particularly at low frequencies. We analyze the excitation of a freely falling two-level atom coupled to quantum fields near the horizon. The associated acceleration-radiation transition probabilities are computed explicitly. The resulting atomic response is locally indistinguishable from that in flat spacetime, confirming the validity of the equivalence principle even in the presence of Lorentz-violating corrections. Finally, we extend the notion of horizon-brightened acceleration radiation (HBAR) entropy to the bumblebee black hole and derive the corresponding entropy production rate induced by infalling atoms.

gr-qc↗

arXiv2025

Comment on "Thermodynamic properties of Schwarzschild black hole in non-commutative gauge theory of gravity"

A recent study [Annals Phys. 455 (2023) 169394, e-Print: 2204.01901 [gr-qc]] examined the thermodynamic behavior of an axially symmetric black hole within a non-commutative framework that mimics the effect of an angular momentum. However, the analysis presents notable computational inconsistencies. In that analysis, the event horizon was miscalculated, and this error propagated through and compromised all subsequent results. In addition, an incorrect definition of surface gravity was used -- the spherically symmetric case was invoked for an axially symmetric spacetime -- rendering the thermodynamic results invalid. In other words, all the results presented in the paper require a thorough reexamination.

gr-qc↗

arXiv2025

Quantum particle production and radiative properties of a new bumblebee black hole

In this work, we investigate the quantum and radiative properties of a recently proposed static bumblebee black hole arising from a general Lorentz-violating vacuum configuration. The analysis begins with the geometric structure of the solution and the thermodynamic temperature obtained from the surface-gravity prescription. The associated thermodynamic topological structure is also examined. Quantum particle production is then analyzed for bosonic and fermionic fields using the tunneling method. Analytic greybody bounds are derived for spin-0, spin-1, spin-2, and spin-1/2 fields. Furthermore, full greybody factors are computed with the sixth-order WKB method, together with the corresponding absorption cross sections and their characteristic spin-dependent peak patterns. These results support the evaluation of the evaporation lifetimes and the emission rates of energy and particle modes associated with each spin contribution, followed by a comparison of the high-frequency regime with other Lorentz-violating geometries, including the \textit{metric} bumblebee, \textit{metric-affine} bumblebee, Kalb-Ramond, and non-commutative Kalb-Ramond black holes. In addition, greybody factors are obtained using a quasinormal-mode-based prescription.

gr-qc↗

arXiv2025

Accretion of matter of a new bumblebee black hole

We investigate how the newly obtained static black hole in bumblebee gravity affects the behavior of accreting matter and its observable signatures. The Lorentz-violating parameter that characterizes this geometry modifies photon trajectories and shifts the location of the critical curve that defines the shadow. Using ray tracing, we examine light deflection, the structure of direct emission, lensing rings, and photon rings, and we explore three thin-disk emission models--starting at the ISCO, at the photon sphere, and at the event horizon--together with static and infalling spherical accretions. Larger values of this parameter enlarge the shadow, move all optical features outward, and suppress the observed intensity through gravitational redshift, with additional dimming produced by Doppler effects for infalling matter

gr-qc↗

arXiv2025

Neutrino oscillations induced by a new bumblebee black hole

This work investigates neutrino propagation in the spacetime of a newly introduced black hole arising from spontaneous Lorentz-symmetry breaking in bumblebee gravity. The analysis focuses on three independent components: the rate at which neutrino-antineutrino annihilation deposits energy in the surrounding region, the geometric contribution to the phase accumulated by neutrino mass eigenstates, and the modifications to flavor conversion produced by weak gravitational lensing. Working with a two-flavor system, both mass orderings are examined, and the calculation incorporates the interference between distinct trajectories reaching the detector. The numerical results show that the Lorentz-violating deformation substantially increases the efficiency of the annihilation channel, produces characteristic shifts in the oscillation phase not present in earlier bumblebee configurations, and reshapes the angular dependence of the lensing-induced flavor transition pattern.

gr-qc↗

arXiv2025

Effects of bumblebee gravity on neutrino motion

This study explores how the spontaneous violation of Lorentz symmetry -- modeled through a black hole solution in the context of bumblebee gravity -- affects the propagation and dynamics of neutrinos. The investigation centers on three distinct aspects: the rate of energy deposition due to neutrino-antineutrino pair annihilation, modifications to the neutrino oscillation phase driven by the underlying spacetime structure, and the influence of gravitational lensing on flavor conversion probabilities. To support the theoretical considerations, numerical simulations are conducted for oscillation probabilities in a two-flavor framework, taking into account both normal and inverted mass orderings. For comparison, the outcomes are juxtaposed with those obtained in a different Lorentz-violating background, namely, a black hole solution within Kalb-Ramond gravity.

gr-qc↗

arXiv2025

Gravitational lensing by a Lorentz-violating black hole

In this work, we study the gravitational lensing by a Lorentz-violating (LV) black hole inspired by the recent contribution [1]. Explicitly, we concentrate on a specific application: we perform the computation of gravitational lensing effects under the strong field limit. In particular, we analytically derive the deflection angle so that the lens equation can also be addressed. This methodological approach yields physically measurable outcomes, including the determination of relativistic image positions and their corresponding magnifications. As an application of this methodology, we consider the gravitational lensing by Sagittarius A${}^*$ and obtain the corresponding observables expressed as functions of the LV parameter.

gr-qc↗

arXiv2025

Axisymmetric black hole in a non-commutative gauge theory: classical and quantum gravity effects

This work explores both classical and quantum aspects of an axisymmetric black hole within a non-commutative gauge theory. The rotating solution is derived using a modified Newman-Janis procedure. The analysis begins with the horizon structure, ergospheres, and angular velocity. The thermodynamic properties are examined through surface gravity, focusing on the Hawking temperature, entropy, and heat capacity. In addition, the remnant mass is calculated. The Hawking radiation is treated as a tunneling process for bosonic and fermionic particles, along with the corresponding particle creation density. Geodesic motion is explored, emphasizing null geodesics, radial accelerations, the photon sphere, and black hole shadows. Finally, the gravitational lensing in the strong deflection limit is investigated.

gr-qc↗

arXiv2025

Particle motion and thermal effects around a Kalb-Ramond black hole

This work is devoted to examining particle dynamics and thermodynamic behavior of a black hole in the framework of Kalb-Ramond gravity, framing the investigation through the lens of the optical-mechanical analogy. Within this context, we derive a generalized modified dispersion relation, which inherently depends on the underlying spacetime geometry through its metric components. The analysis begins by exploring some physical quantities influenced by the geometry, including the effective index of refraction, the group velocity, and the time delay experienced by particle modes. We then investigate the interparticle potential, considering both massive and massless cases. The thermodynamic properties of the system are subsequently addressed using ensemble theory. In this treatment, we compute the pressure, internal energy, entropy, and heat capacity across three distinct regions: in the immediate vicinity of the event horizon, at the photon sphere, and in the asymptotic region. Notably, all calculations presented throughout this paper admit closed-form analytical solutions.

gr-qc↗

arXiv2025

A Non-Commutative Kalb-Ramond Black Hole

This work presents a new black hole solution within the framework of a non-commutative gauge theory applied to Kalb-Ramond gravity. Using the method recently proposed in the literature [Nucl.Phys.B 1017 (2025) 116950], we employ the Moyal twist $\partial_r \wedge \partial_θ$ to implement non-commutativity, being encoded by parameter $Θ$. We begin by verifying that the resulting black hole no longer possesses spherical symmetry, while the event horizon remains unaffected by non-commutative corrections. The Kretschmann scalar is computed to assess the corresponding regularity. It turns out that the solution is regular, provided that the Christoffel symbols and related quantities are not expanded to second order in $Θ$. We derive the thermodynamic quantities, including the Hawking temperature $T^{(Θ,\ell)}$, entropy $S^{(Θ,\ell)}$, and heat capacity $C_V^{(Θ,\ell)}$. The remnant mass $M_{\text{rem}}$ is estimated by imposing $T^{(Θ,\ell)} \to 0$, although the absence of a physical remnant indicates complete evaporation. Quantum radiation for bosons and fermions is analyzed via the tunneling method, where divergent integrals are treated using the residue theorem. Notably, in the low-frequency regime, the particle number density for bosons surpasses that of fermions (at least within the scope of the methods considered here). The effective potential for a massless scalar field is obtained perturbatively, enabling the computation of quasinormal modes and the time-domain profiles. Finally, further bounds on $Θ$ and $\ell$ (Lorentz-violating paramter) are derived from solar system tests, including the perihelion precession of Mercury, light deflection, and the Shapiro time delay.

gr-qc↗

arXiv2025

Gravitational signatures of a nonlinear electrodynamics in $f(R,T)$ gravity

In this work, we investigate a nonlinear electrodynamics model within the framework of $f(R,T)$ gravity. We begin by outlining the general features of the theory and analyzing the event horizon under conditions ensuring its real and positive definiteness. We then examine light trajectories, focusing on critical orbits, shadow radii, and geodesics of massless particles. The parameters $α$ and $β$, associated with the nonlinear extension of the Reissner-Nordström spacetime, are constrained using observational data from the Event Horizon Telescope (EHT). Subsequently, we analyze the thermodynamic properties of the system, including Hawking temperature, entropy, and heat capacity. Quasinormal modes are computed for scalar, vector, tensor, and spinorial perturbations, with the corresponding time-domain profiles explored as well. Gravitational lensing is then studied in both weak and strong deflection limits, along with the stability of photon spheres. Finally, we examine additional topological aspects, including topological thermodynamics and the topological photon sphere.

gr-qc↗

arXiv2025

Particle production induced by a Lorentzian non-commutative spacetime

In this paper, we examine particle production, evaporation, and greybody factors for a Lorentzian non-commutative black hole. We begin by analyzing particle creation for bosons, considering scalar perturbations to compute the Bogoliubov coefficients, which enable the determination of the Hawking temperature $T_Θ$. Subsequently, we describe Hawking radiation as a tunneling process using the Painlevé-Gullstrand metric representation, allowing the evaluation of divergent integrals via the residue method. This approach yields the particle creation density for bosonic modes. Next, we extend the analysis to fermions, obtaining the corresponding particle creation density. The black hole evaporation is then examined through the Stefan-Boltzmann law, leading to an estimate of the black hole's lifetime. In this context, we identify the presence of a remnant mass when the black hole reaches the final stage of its evaporation. Furthermore, we compute greybody factors for bosons, taking into account scalar, vector, and tensorial perturbations. Finally, we determine the greybody factors for fermions as well. Overall, compared to the Schwarzschild case ($Θ= 0$), the presence of the non-commutative parameter $Θ$ lowers the Hawking temperature and reduces the particle creation density for both bosons and fermions, causing the evaporation process to proceed more slowly. Additionally, $Θ$ decreases the magnitude of the greybody factors for bosons and fermions across all perturbations considered in this analysis.

gr-qc↗

arXiv2025

Comment on "Quantum tunneling from Schwarzschild black hole in non-commutative gauge theory of gravity"

The particle creation via quantum tunneling was recently calculated for the Schwarzschild non-commutative black hole solution in Ref. [Phys. Lett. B 848 (2024) 138335, e-Print: 2310.02445 [gr-qc]]. Nevertheless, it contains inconsistencies in the calculations that need to be properly corrected. In particular, the event horizon was incorrectly determined in that work, which affected all the subsequent calculations. Moreover, the same issue have been repeated elsewhere by the same authors in Refs. [1-4].

gr-qc↗

arXiv2025

Non-commutativity in Hayward spacetime

In this work, we propose a new black hole solution, namely, a Hayward-like metric incorporating corrections due to non-commutativity by taking into account $\partial_r\wedge\partial_θ$ Moyal twist. We begin by deriving this solution using the non-commutative gauge theory framework. The general properties of the metric are then analyzed, including the event horizon structure and the Kretschmann scalar. Analogous to the standard Hayward solution, the modified black hole remains regular, provided that additional dependence on the angle $θ$. Next, we examine the thermodynamic properties, computing the Hawking temperature, entropy, and heat capacity. From the temperature profile, we verify that there is no physical remnant mass when $T^{(Θ,l)} \to 0$, indicating a complete evaporation process. Quantum radiation is analyzed by considering both bosonic and fermionic particle modes, with an estimation of the particle creation density provided for each case. The effective potential is evaluated perturbatively to accomplish the analysis of quasinormal modes and the time-domain response for scalar perturbations. The study of null geodesics is explored to enable the characterization of the photon sphere and black hole shadows. Additionally, constraints on the shadows are estimated based on EHT (Event Horizon Telescope) data. Furthermore, the Gaussian curvature is determined to assess the stability of critical orbits, followed by an analysis of gravitational lensing using the Gauss-Bonnet theorem. Finally, the constraints (bounds) on the parameters $Θ$ (non-commutativity) and $l$ (``Hayward parameter'') are derived based on solar system tests, including the perihelion precession of Mercury, light deflection, and the Shapiro time delay effect.

gr-qc↗

arXiv2025

Influence of a Kalb-Ramond black hole on neutrino behavior

In this work, we investigate the consequences of Lorentz symmetry breaking induced by a black hole solution within Kalb-Ramond gravity on neutrino dynamics. The analysis is structured around three key phenomena: the energy output associated with neutrino-antineutrino annihilation, the impact of spacetime geometry on the oscillation phases of neutrinos, and the changes in flavor transition probabilities caused by gravitational lensing effects. To complement the theoretical framework, we also carry out a numerical evaluation of neutrino oscillation probabilities, comparing scenarios of normal and inverted mass orderings within a two-flavor approximation.

gr-qc↗