Searcharxiv⌕ Search

arXiv subjects

C. A. S. Almeida

Publications and source records attributed to C. A. S. Almeida.

At least 37 records · Page 2Linked to original sources
arXiv2025

Perturbative solutions for compact objects in (2+1)-dimensional Bopp-Podolsky electrodynamics

We investigate the space-time geometry generated by compact objects in (2+1)-dimensional Bopp-Podolsky electrodynamics. Inspired by previous studies where the Bopp-Podolsky field acts as a source for spherically symmetric solutions, we revisit this question within the lower-dimensional (2+1) framework. Using a perturbative approach, we derive a charged BTZ-like black hole solution and compute corrections up to second order in a perturbative expansion valid far from the horizon. Our analysis suggests that the near-horizon and inner structure of the solution remain unaltered, indicating that no new non-black hole objects emerge in this regime. In particular, we do not find evidence of wormhole solutions in the (2+1)-dimensional version of this theory.

gr-qc↗
arXiv2025

On the singular position-dependent mass

Revisiting the issue associated with Position-Dependent Mass (PDM), we reaffirm that the appropriate framework for addressing a generic PDM is the symmetrization proposed by BenDaniel and Duke. To accomplish this result adopts the effective mass Hamiltonian proposed by von Roos, corrected by a symmetrized kinematic term. After verifying the appropriate ordering to approach the PDM issue, one investigates a crystalline lattice with a defect described by a singular PDM. The singular mass profile proves intriguing as it yields an atom's cluster in the neighborhood of the singularity. Considering that a restoring force acts on the atoms, one notes that the confluent Heun function describes the quantum states. Furthermore, one highlights that when the effective mass distribution tends to a constant profile, we recover a system similar to the harmonic oscillator.

quant-ph↗
arXiv2024

Kinks and double-kinks in generalized $ϕ^{4}$-and $ϕ^{8}$-models

Examining the $ϕ^{4}$ and $ϕ^{8}$ models within a two-dimensional framework in the flat spacetime and embracing a theory with unconventional kinetic terms, one investigates the emergence of kinks/antikinks and double-kinks/antikinks. We devote our study to obtaining the field configurations with minimal energy, i.e., solutions possessing a Bogomol'nyi-Prasad-Sommerfield's bound. Next, to accomplish our goal, we adopt non-polynomial generalizing functions, namely, hyperbolic sine and cosine functions: the first produce BPS potentials exhibiting a minimum at $ϕ=0$, facilitating the emergence of genuine double-kink-type configurations. Conversely, the second promotes the rise of kink-type solutions.

hep-th↗
arXiv2024

On the asymmetric non-canonical braneworld in five dimensions

Revisiting Einstein's gravitational theory, we build a five-dimensional braneworld. Within this framework, one announces the appearance of symmetric and asymmetric domain walls. Furthermore, it examines the emergent four-dimensional gravity from a theory with non-canonical dynamics. Exploring the physical and mathematical aspects, e.g., brane's energy density and the Kaluza-Klein (KK) spectrum, one verifies that brane splitting is absent in the canonical and non-canonical theories. Additionally, we note the localization of the four-dimensional fluctuation projection on the 3-branes, which ensures the theory's stability. Thereby, one can conclude that the behavior of gravitational perturbations of the domain wall maintains a profile similar to a stable and non-localizable tower of massive modes. In contrast, within the brane core, the matter sector generates new barriers and potential wells, resulting in massive modes with approximately symmetric amplitudes. However, the non-canonical dynamics generate massive modes with asymmetric amplitudes far from the 3-brane.

gr-qc↗
arXiv2024

Effects of quantum fluctuations of the metric on a braneworld

Adopting the premise that the expected value of the quantum fluctuating metric is linear, i.e., $\langle g^{μν}\rangle=αg^{μν}$, we analyze the modified gravity theory induced by the Einstein-Hilbert action coupled to a matter field. This approach engenders the $f(R,T)$ gravity used to investigate the braneworld. In this scenario, considering a thick brane, the influence of metric fluctuations on brane dynamics is investigated. Consequently, one shows how the metric fluctuations influence the vacuum states. This influence has repercussions for modifying the brane energy and the asymptotic profile of the matter field. After noticing these modifications, we analyzed the most likely and stable structures from the matter field. One performs this analysis considering the theoretical measure of differential configurational entropy.

gr-qc↗
arXiv2024

Electronic states in quantum wires on a Möbius strip

We study the properties of a two-dimensional non-relativistic electron gas (TDEG) constrained on wires along a Möbius strip. We considered wires around the strip and along the transverse direction, across the width of the strip. For each direction, we investigate how the curvature modifies the electronic states and their corresponding energy spectrum. At the center of the strip, the wires around the surface form quantum rings whose spectrum depends on the strip radius $a$. For wires at the edge of the strip, the inner edge turns into the outer edge. Accordingly, the curvature yields localized states in the middle of the wire. Along the strip width, the effective potential exhibits a parity symmetry breaking leading to the localization of the bound state on one side of the strip.

cond-mat.mes-hall↗
arXiv2024

Physical aspects of the deformation of $\mathbb{Z}_2$ kinks in a generalized $ϕ^4$ model

We study a generalized $ϕ^4$ model that gives rise to BPS kink/antikink configurations with compacton-like profiles. One observes that the positive parameter controlling the generalizing function promotes an infinity degenerescence of the BPS solutions. We then use the Differential Configurational Complexity technique to distinguish the degenerate configurations, which allows us to obtain the parameter values providing the most likely field profiles. Besides, the analysis of the excitation spectrum of the model shows the existence of translational and vibrational modes. Thus, the emergence of bound states of solitons (bions) and resonance phenomena is guaranteed when analyzing the scattering of kink/antikink structures. In this way, one notes that depending on the initial velocity, the collision can be inelastic or quasi-elastic, even in the case of compacton-like configurations.

hep-th↗
arXiv2024

Braneworlds in Warped Einsteinian Cubic Gravity

Einstenian cubic gravity (ECG) is a modified theory of gravity constructed with cubic contractions of the curvature tensor. This theory has the remarkable feature of having the same two propagating degrees of freedom of Einstein gravity (EG), at the perturbative level on maximally symmetric spacetimes. The additional unstable modes steaming from the higher order derivative dynamics are suppressed provided that we consider the ECG as an effective field theory wherein the cubic terms are seen as perturbative corrections of the Einstein-Hilbert term. Extensions of ECG have been proposed in cosmology and compact objects in order to probe if this property holds in more general configurations. In this work, we construct a modified ECG gravity in a five dimensional warped braneworld scenario. By assuming a specific combination of the cubic parameters, we obtained modified gravity equations of motion with terms up to second-order. For a thin 3-brane, the cubic-gravity corrections yield an effective positive bulk cosmological constant. Thus, in order to keep the 5D bulk warped compact, an upper bound of the cubic parameter with respect to the bulk curvature was imposed. For a thick brane, the cubic-gravity terms modify the scalar field potential and its corresponding vacuum. Nonetheless, the domain-wall structure with a localized source is preserved. At the perturbative level, the Kaluza-Klein (KK) tensor gravitational modes are stable and possess a localized massless mode provided the cubic corrections are small compared to the EG braneworld.

gr-qc↗
arXiv2023

String-like brane splitting in the context of $f(T,B)$ gravity

In this work, the influence of the boundary term $B$ is analyzed in a string-like thick brane scenario in the gravity context $f(T, B)$. For that, three models of $f(T, B)$ are proposed, i.e., $f_1(T, B)=T+k{B}^{n}$, $f_2(T, B)=T+k(-T+B)^{n}$ and $f_3(T, B)=T+k_1T^2+k_2{B}^2$, where $n$, $k$ and $k_{1,2}$ are parameters that control the deviation from the usual teleparallelism. The first relevant result obtained was the appearance of a super-located tower in the core for energy density. Furthermore, the greater the influence of the boundary term, the new maximums and minimums appear in the energy density. All this indicates the emergence of capable structures from split to the brane. The second relevant result was obtained by analyzing the gravitational perturbations, where the effective potential presents the supersymmetric form of quantum mechanics, leading to well-localized massless modes.

gr-qc↗
arXiv2023

Aspects of kink-like structures in 2D dilaton gravity

The topological structures that arise from two-dimensional models are relevant physically and the first step towards understanding more complex systems. In this work, one studies the kink-like solutions of the matter field that emerge in a two-dimensional dilaton gravity scenario. Considering this scenario, we examine the linear stability of the matter field and the translational mode. Due to the specific profile of the solutions found, a differential configurational complexity (DCC) analysis of the system was necessary to confirm the nature of the structures. Furthermore, we study the interforce and scattering process, considering a pair of kink-antikink-like solutions in a fixed time ($t=0$).

hep-th↗
arXiv2023

Dirac fermions on wires confined to the graphene Moebius strip

We investigate the effects of the curved geometry on a massless relativistic electron constrained to a graphene strip with a Moebius strip shape. The anisotropic and parity-violating geometry of the Moebius band produces a geometric potential that inherits these features. By considering wires along the strip width and the strip length, we find exact solutions for the Dirac equation and the effects of the geometric potential on the electron were explored. In both cases, the geometric potential yields to a geometric phase on the wave function. Along the strip width, the density of states depends on the direction chosen for the wire, a consequence of the lack of axial symmetry. Moreover, the breaking of the parity symmetry enables the electronic states to be concentrated on the inner or on the outer portion of the strip. For wires along the strip length, the nontrivial topology influences the eigenfunctions by modifying their periodicity. It turns out that the ground state has a period of $4π$ whereas the first excited state is a $2π$ periodic function. Moreover, we found that the energy levels are half-integer multiples of the energy of the ground state.

cond-mat.mes-hall↗
arXiv2023

Topological solitons in the sigma-cuscuton model

Building a multi-field theory with canonical and non-canonical contributions, one studies the topological solitons of the O(3)-sigma model. We propose a model constituted by the O(3)-sigma field, the cuscuton-like neutral scalar field, and Maxwell's field. We investigate BPS properties considering a theory without interaction. One performs this study by adopting the first-order formalism in a model with contribution non-canonical. Thus, these contributions will preserve the spontaneous symmetry breaking of the system. Concurrently, a non-minimal coupling between the sigma and the Maxwell field is assumed. In this scenario, interesting results arise, i.e., one notes that the solitons have an internal structure and ring-like profile. Furthermore, one observes that the ring-like configurations that emerge are directly related to the contribution of the cuscuton-like term.

hep-th↗
arXiv2023

5D Elko spinor field non-minimally coupled to nonmetricity in $f(Q)$ gravity

This paper aims to investigate the localization of the five-dimensional spinor field known as Elko (dual-helicity eigenspinors of the charge conjugation operator) by employing a Yukawa-like geometrical coupling in which the Elko field is non-minimally coupled to nonmetricity scalar $Q$. We adopt the braneworld scenarios in which the first-order formalism with sine-Gordon and linear superpotentials is employed to obtain the warp factors. A linear function supports the zero-mode trapping within the geometric coupling, leading to the same effective potential as the scalar field. Moreover, an exotic term must be added to obtain real-valued massive modes. Such modes are investigated through the Schrödinger-like approach.

gr-qc↗
arXiv2023

Localization of abelian gauge fields with Stueckelberg-like geometrical coupling on $f(T,B)$-thick brane

In the context of $f(T,B)$ modified teleparallel gravity, we investigate the influence of torsion scalar $T$ and boundary term $B$ on the confinement of both the gauge vector and Kalb-Ramond fields. Both fields require a suitable coupling in five-dimensional braneworld scenarios to yield a normalizable zero mode. We propose a Stueckelberg-like geometrical coupling that non-minimally couples the fields to the torsion scalar and boundary term. To set up our braneworld models, we use the first-order formalism in which two kinds of superpotential are taken: sine-Gordon and $ϕ^{4}$-deformed. The geometrical coupling is used to produce a localized zero mode. Moreover, we analyze the massive spectrum for both fields and obtain possible resonant massive modes. Furthermore, we do not find tachyonic modes leading to a consistent thick brane.

gr-qc↗
arXiv2023

Properties of black hole vortex in Einstein's gravity

We investigate the influence of the matter field and the gauge field on the metric functions of the AdS$_3$ spacetime of the Maxwell-Higgs model. By considering a matter field with a solitonic profile with the ability to adjust the field variable from kink to compact-like configurations, the appearance of black hole solutions is noticed for an event horizon at $r_{+} \approx 1.5$. An interesting result is displayed when analyzing the influence of matter field compactification on the metric functions. As we obtain compact-like field configurations the metric functions tend to a ``linearized behavior''. However, the compactification of the field does not change the structure of the horizon of the magnetic black hole vortex. With the ADM formalism, the mass of the black hole vortex is calculated, and its numerical results are presented. By analyzing the so-called ADM mass, it is observed that the mass of the black hole vortex increases as the cosmological constant becomes more negative, and this coincides with the vortex core becoming smaller. Nonetheless, this mass tends to decrease as the solitonic profile of the matter field becomes more compacted. Then, the black hole temperature study is performed using the tunneling formalism. In this case, it is perceived that the cosmological constant, and the $α$-parameter, will influence the Bekenstein-Hawking temperature. In other words, the temperature of the structure increases as these parameters increase.

gr-qc↗
arXiv2023

Quantum information entropy of a particle trapped by the Aharonov-Bohm-type effect

In this research article, we use the Shannon's formalism to investigate the quantum information entropy of a particle trapped by the Aharonov-Bohm-type effect. For quantum information study, it is necessary to investigate the eigenstates of the quantum system, i. e., the wave functions and energies of the quantum states. We assumed that the particle is in principle, confined in a cylindrical box in the presence of an Aharonov-Bohm-type effect due to dislocation defect. Analysis of the quantum information entropy, reveals that the dislocation influences the eigenstates and, consequently, the quantum information of the system.

quant-ph↗
arXiv2023

Non-Hermitian fermions with effective mass

In this work, we readdress the Dirac equation in the position-dependent mass (PDM) scenario. Here, one investigates the quantum dynamics of non-Hermitian fermionic particles with effective mass assuming a $(1+1)$-dimension flat spacetime. In seeking a Schrödinger-like theory with PT symmetry is appropriate to assume a complex potential. This imaginary interaction produces an effective potential purely dependent on mass distribution. Furthermore, we study the non-relativistic limit by adopting the Foldy-Wouthuysen transformation. As a result, that limit leads to an ordering equivalent to the ordering that describes abrupt heterojunctions. Posteriorly, particular cases of mass distribution also were analyzed. Thus, interesting results arise for the case of a linear PDM, which produces an effective harmonic oscillator and induces the emergence of bound states. For a hyperbolic PDM, an effective potential barrier emerges. However, in this case, the fermions behave as free particles with positive-defined energy.

quant-ph↗
arXiv2023

Quantum information entropy of heavy mesons in the presence of a point-like defect

Using Schrödinger's formalism, we investigate the quantum eigenstates of the heavy mesons trapped by a point-like defect and by Cornell's potential. One implements this defect to the model considering a spherical metric profile coupled to it. Furthermore, the Nikiforov-Uvarov method is applied to theory to study the quantum eigenstates of the heavy mesons. To calculate the quantum information entropy (QIE), one considers the wave functions that describe the charmonium and bottomonium states. To explore the QIE, we use the well-known Shannon's entropy formulated at the position and reciprocal space. The analysis of the QIE gives us relevant information about how the quantum information change with the variation of the point-like defect. Consequently, considering the Bialynicki-Birula and Mycielski (BBM) relation, we show how this defect influences the quarkonium position and momentum uncertainty measures.

hep-ph↗