arXiv subjects

E. Passos

Publications and source records attributed to E. Passos.

At least 19 recordsLinked to original sources

arXiv2026

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 $\alpha$. 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↗

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 $\alpha_\phi$, on the Casimir effect within a five-dimensional flat spacetime. By considering a quasiperiodic condition regulated by the parameter $\beta$ 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 $\beta$ acts as a crucial control parameter, enabling a continuous transition between attractive and repulsive regimes, with a characteristic symmetry around $\beta = 0.5$. We show that the Lorentz-violating parameter $\alpha_\phi$ 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

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 $\lambda$ 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↗

arXiv2025

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↗

arXiv2025

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↗

arXiv2025

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↗

arXiv2025

Bound states around vacuum in scalar ModMax model

In this work, we consider a two-dimensional scalar field model inspired by the dimensional reduction of a four-dimensional ModMax theory. Upon projecting out the 4D theory down to a 2D theory we obtain a theory which presents a constant electric field and two scalar fields. In order to investigate kinks, we include the presence of a potential and consider the static case with one of the fields in the vacuum, showing that the solutions for the non-uniform field can be mapped into the ones arising from the canonical model. By studying the linear stability of the model, we show that fluctuations around the uniform field are described by a Sturm-Liouville eigenvalue equation whose weight function depends on the non-uniform solution and the parameter of the ModMax model. Remarkably, the presence of the aforementioned weight may bring bound states to light, contrary to what occurs in the canonical model.

hep-th↗

arXiv2025

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↗

arXiv2024

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↗

arXiv2024

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↗

arXiv2024

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↗

arXiv2023

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↗

arXiv2023

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↗

arXiv2023

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↗

arXiv2023

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↗

arXiv2023

Hawking radiation and entropy of a BTZ black hole with minimum length

In this paper we consider a BTZ black hole with minimum length which has been introduced through the probability density of the ground state of the hydrogen atom. We analyzed the effect of the minimum length by calculating the thermodynamic quantities such as temperature and entropy and verified the stability of the black hole by computing the specific heat capacity.

hep-th↗

arXiv2022

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↗

arXiv2022

Absorption, scattering and shadow by a noncommutative black hole with global monopole

In this paper, we investigate the process of massless scalar wave scattering due to a noncommutative black hole with a global monopole through the partial wave method. We computed the cross section of differential scattering and absorption at the low frequency limit. We also calculated, at the high frequency limit, the absorption and the shadow radius by the null geodesic method. We showed that noncommutativity causes a reduction in the differential scattering/absorption cross section and shadow radius, while the presence of the global monopole has the effect of increasing the value of such quantities. In the limit of the null mass parameter, we verify that the cross section of differential scattering, absorption and shadow ray approach to a non-zero value proportional to a minimum mass.

hep-th↗