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M. A. Anacleto

Publications and source records attributed to M. A. Anacleto.

At least 19 recordsLinked to original sources

Shadow of a Noncommutative Thin-Shell Gravastar

One of the main challenges in astronomy is the direct observation of black holes. However, distinguishing black holes from ultra-compact horizonless objects through photon observations can be difficult, since the latter may also possess unstable circular photon orbits. An example of an Ultra-Compact Object is a Gravastar (gravitational vacuum star), initially proposed by Mazur and Mottola. For definition purposes, we construct a spherically symmetric thin-shell gravastar model within a noncommutative model, in which these effects are integrated by a Lorentzian distribution of the energy density with a minimum width $\sqrtθ$. The model is constructed using the cut-and-paste technique to connect a nonsingular de Sitter interior to a noncommutative Schwarzschild exterior, satisfying the Israel junction conditions on the interface hypersurface $Σ$. We examine the stability of the model through its energy conditions, highlighting the influence of the noncommutative parameter on its behavior. {Model stability was also investigated using the parameter $η$, derived from the linearized stability analysis.} We also show that, owing to noncommutativity, the photon trajectories and deflection angles change as the noncommutative parameter increases. Our proposed gravastar model, with noncommutative geometry on its exterior, can be considered a stable and viable alternative to the charged black hole in the context of this type of gravity.

gr-qc

Absorption and quasinormal modes by rotating acoustic black holes in Lorentz-violating background

In this work, we investigate the effects of Lorentz symmetry violation on the absorption cross section and quasinormal modes of a rotating acoustic black hole in (2+1) dimensions, within the regime of slow rotation and small Lorentz violating parameter $α$. The absorption cross section was analyzed analytically, using the low and high frequency regimes, and numerically, through integration of the radial equation. The results showed that, in this regime, Lorentz violation increases the absorption cross section at all energy scales, with a contribution from the rotation parameter $B$ appearing even in the low frequency regime. For the quasinormal modes, we observed that symmetry breaking decreases the real part of the frequencies and increases the magnitude of the corresponding imaginary part, indicating a faster damping of the oscillations.

gr-qc

The Lorentz-Violating effects in charged particle systems

We investigate the relativistic dynamics of a spin half particle in the presence of a Lorentz-violating background within the framework of effective field theory. A modified Dirac Hamiltonian is considered, arising from a CPT odd coupling involving the Lorentz violating gauge tensor of the Standard Model Extension (SME). The velocity and effective force operators are derived from the Heisenberg equations of motion. Using Ehrenfest s theorem and the correspondence principle, we obtain the classical limit of the dynamics and identify an effective force exhibiting a generalized Lorentz force structure. This formalism is applied to a Penning trap system, known for its high precision measurements of charged particle properties. Our analysis shows that the effective cyclotron frequency acquires a correction due to the Lorentz violating term, leading to deviations in the particle trajectory and offering a potentially observable signature of Lorentz violation in precision experiments. By comparing our results with current bounds from high precision Penning traps, we establish an upper limit on the Lorentz violating coupling, $\bar{g}k_{AF}\lesssim 2.32 \times 10^{4}\mathrm{eV}^{-1}$ corresponds to LIV effects. This bound is compatible with the interpretation of an effective Lorentz violation, consistent with current observational constraints, and it reinforces the phenomenological nature of the term under consideration, in agreement with previous analyses based on cosmological birefringence and photon propagation in a Lorentz violating background.

hep-ph

Thin-shell gravastar model in a BTZ geometry with minimum length

In this paper, we construct two spherically symmetric thin-shell gravastar models within a BTZ geometry with minimum length. Therefore, in the inner region of the gravastar, we consider an anti- de Sitter metric with minimum length. Thus, for the first model, we introduce the minimum length effect using the probability density of the ground state of the hydrogen atom in two dimensions. For the second gravastar model, we adopt a Lorentzian-type distribution. Also in the outer region, we consider the BTZ black hole metric. So, by examining the inner spacetime, the thin shell, and the outer spacetime, we find that there are different physical characteristics regarding their energy densities and pressures that make the gravastar stable. This effect persists even when the cosmological constant is zero. In addition, we determined the entropy of the gravastar thin shell. Besides, we explore the thermodynamic properties of the BTZ black hole with minimum length in Schwarzschild-type form and also check its stability.

gr-qc

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

Stefan-Boltzmann Law and Thermal Casimir Effect in Neutron Star Spacetime via Thermo Field Dynamics

We investigate the thermal Casimir effect for a massless scalar field in the curved spacetime of a neutron star within the Thermo Field Dynamics (TFD) formalism. Starting from the renormalized energy-momentum tensor, we generalize the Stefan-Boltzmann law to include gravitational redshift and curvature corrections governed by the Tolman-Oppenheimer-Volkoff (TOV) metric. Finite temperature and spatial compactification are introduced simultaneously, allowing a unified and consistent treatment of both vacuum and thermal contributions inside and outside the star. Analytical expressions are derived for the high- and low-temperature limits, showing explicitly how curvature and redshift modify the characteristic $T^4$ dependence of thermal radiation. The results reveal that strong gravity significantly alters the local energy density and pressure, demonstrating the nontrivial interplay between quantum vacuum fluctuations and compact astrophysical geometries. A polytropic model is considered to perform numerical analyses, highlighting the influence of the spacetime background on vacuum fluctuations.

gr-qc

The 2D Lorentz-violating fermionic Casimir effect under thermal conditions

In the present work, we study a fermionic Lorentz invariance violation (LIV) theory with a CPT-even extension and analyze its impact on the Casimir effect under the MIT bag boundary condition model in a low-dimensional setting, where results are obtained without any approximations for a null-temperature system. Moreover, the Matsubara formalism is applied to derive closed expressions for the influence of temperature on the physical observables: Casimir energy, Casimir force, and entropy associated with the system in a LIV context. For each thermal observable, the influence of the LIV correction term is considered in the analysis of both low- and high-temperature regimes. Additionally, we construct a condensed matter analogue using the SSH model, where nonlinear fermionic dispersion and boundary-induced vacuum energy emerge, reproducing the analytical structure of the LIV Casimir effect.

hep-th

On global vortices in the higher derivative Lorentz-violating scenario

We study the influence of Lorentz invariance violation (LIV) background in energy regularization of global structures in $(2, 1)$--dimensions. To this end, we consider a model in which the complex scalar and fixed three-vector couple as a high derivative order term. We show that LIV-background does not affect the energy and the equation of motion of neutral global structures. However, we observe that the charged structures are sensitive to LIV-background by presenting signatures in the electric field whose intensity is controlled by the LIV-parameter. Furthermore, the procedure developed leads to first-order solutions with finite energy and a regularized electric field.

hep-th

Gravitational Dipole Moment in Braneworld Model

We investigate the gravitational effects on the relativistic Dirac theory of a system such as a Hydrogen atom in the braneworld scenario. A gravitational dipole moment like contribution, arises in the nonrelativistic Hamiltonian of the system through an exact Foldy-Wouthuysen transformation. This term violates the equivalence principle for the weak interaction that is restored in the average over the spins. Furthermore, it feels the effects of the extra dimensions, so that in a Universe with two additional spatial dimensions its energy contribution is amplified by an order of $\sim 10^{16}\ \text{eV}$ concerning to the energy of this term for ordinary space. The compactification radius for a Universe with two extra dimensions is within the experimental limits, where deviations from the inverse square law are being tested. This suggests that the energy value for the gravitational dipole term in this scenario may lead us to search for traces of extra dimensions in atomic spectroscopy, as well as experimental constraints for these dimensions.

gr-qc

The self-dual Lorentz violating model: quantization, scattering and dual equivalence

In this paper, we analysis the dynamics, at the quantum level, of the self-dual field minimally coupled to bosons with Lorentz symmetry breaking. We quantize the model by applying the Dirac bracket canonical quantization procedure. In addition, we test the relativistic invariance of the model by computing the boson-boson elastic scattering amplitude. Therefore, we show that the Lorentz symmetry breaking has been restored at the quantum level. We finalize our analysis by computing the dual equivalence between the self-dual model with Lorentz symmetry breaking coupled with bosonic matter and the Maxwell-Chern-Simons with Lorentz invariance violation coupled with bosonic field.

hep-th

Scattering and absorption by extra-dimensional black holes with GUP

In this paper, we consider the Schwarzschild-Tangherlini black hole to investigate the process of scalar wave scattering by the black hole in a spacetime of (d + 1) dimensions and also with the generalized uncertainty principle (GUP). In this scenario, we analytically determine the phase shift and explore the effect of extra dimensions by calculating the differential scattering and absorption cross-section by applying the partial wave method at low and high-frequency limits. We show at high dimensions that the absorption is not zero as the mass parameter approaches zero.

gr-qc

Absorption, scattering, quasinormal modes and shadow by canonical acoustic black holes in Lorentz-violating background

In the present work, we study the scattering for a black hole described by the canonical acoustic metric with Lorentz violation using asymptotic and numerical methods. In this scenario, we also check the effects of quasinormal modes and the acoustic shadow radius. In the eikonal limit the relationship between the shadow radius and the real part of the quasinormal frequency is preserved.

gr-qc

Aether-Electromagnetic theory and the Casimir effect

In this study, we explore the impact of an additional dimension, as proposed in Kaluza-Klein's theory, on the Casimir effect within the context of Lorentz invariance violation (LIV), which is represented by the ``aether field''. We demonstrate that the Casimir energy is directly influenced by the presence of the fifth dimension, as well as by the aether parameter. Consequently, the force between the plates is also subject to variations of these parameters. Furthermore, we examine constraints on both the size of the extra dimension and the aether field parameter based on experimental data. The LIV parameter can provide insights into addressing the size-related challenges in Kaluza-Klein's theory and offers a mean to establish an upper limit on the size of the extra dimension. This helps to rationalize the difficulties associated with its detection in current experiments.

hep-th

Two-dimensional Lorentz-violating Casimir effect

In this study, we consider the four-dimensional Maxwell electrodynamics extended with CPT-even Myers-Pospelov Lorentz-violating dimension-six operators to investigate the associated two-dimensional properties in the context of quantum vacuum fluctuation effects, namely, the Casimir effect. Upon projecting out the 4D theory down to a 2D theory we obtain analogs of these operators leading to a modified dispersion relation in a Lorentz invariance violation (LIV) scalar model equivalent to the electromagnetic theory. By making use of the modified dispersion relation, we derive exact analytic expressions for the Casimir energy and force induced by imposing Dirichlet boundary conditions on the scalar field. In the regime where the LIV parameter becomes very small, we recover known results for the Casimir energy and force plus correction terms due to the LIV.

hep-th

Thin-shell gravastar in a noncommutative BTZ geometry

In this paper, we build a thin-shell gravastar model within a noncommutative BTZ geometry. For this, we consider a noncommutative BTZ metric in the inner region and a geometry associated with a BTZ solution in the outer region, joined by the generalized join technique. After investigating the inner spacetime, surface and outer spacetime, we observe that there is a surface energy density and surface pressure, such as to make gravastar stable. This effect persists even when the cosmological constant is zero. Besides, we found a bound for the noncommutativity parameter. In addition, we examine the thermodynamics of the noncommutative BTZ black hole in Schwarzschildtype form in three-dimensional spacetime. We also check the stability condition by calculating the specific heat capacity.

gr-qc

Radiatively induced finite and (un)determined Chern-Simons-like terms

The problem of Chern-Simons-like term induction via quantum corrections in four-dimensions is investigated in two different cases. In the first case, we consider two distinct approaches to deal with the exact fermion propagator of the extended QED theory up to the first order in the $b$-coefficient. We find different results for distinct approaches in the same regularization scheme. In the second case, we show that when we use a modified derivative expansion method and another regularization scheme, we obtain a result that exactly coincides with one of the results obtained in the former case. This seems to imply an ambiguity absence as one treats the fermion propagator and the self-energy tensor properly.

hep-th

Hawking radiation and stability of the canonical acoustic black holes

In this paper we determine the Hawking temperature and entropy of a modified canonical acoustic black hole. In our results we obtain an entropy-area relation that has a logarithmic correction term in leading order. We also analyze the stability condition of the noncommutative canonical acoustic black hole and also with quantum corrections implemented by the generalized Heisenberg uncertainty principle.

hep-th

Modified metrics of acoustic black holes: A review

In this brief review, we will address acoustic black holes arising from quantum field theory in the Lorentz-violating and non-commutative background. Thus, we consider canonical acoustic black holes with effective metrics for the purpose of investigating Hawking radiation and entropy. We show that due to the generalized uncertainty principle and the modified dispersion relation, the Hawking temperature is regularized, that is, free from the singularity when the horizon radius goes to zero. In addition, we also find logarithmic corrections in the leading order for entropy.

hep-th