arXiv subjects

Claudio Furtado

Publications and source records attributed to Claudio Furtado.

At least 19 recordsLinked to original sources

arXiv2026

Exact scalarization thresholds and onset laws for a nonminimally coupled scalar field on the Ellis wormhole

We study a real scalar field nonminimally coupled to curvature on a fixed Ellis wormhole background. The scalar perturbation decouples at linear order, and the substitution $ x=a \tan z $ reduces its static radial equation to a trigonometric Pöschl-Teller problem. This yields the exact threshold spectrum $ ζ_{n\ell}=(n+\ell+1)^2/2 $, closed-form Gegenbauer profiles, and an exact count of negative radial eigenvalues in each angular sector. The s-wave thresholds are zero-energy resonances at which the growth rate rises linearly, whereas the $ \ell \geq1\ $ threshold states are square integrable and the growth rate rises as a square root. At the first threshold we also obtain the next-order term, $ σa=(π/4)g-(3π/16)g^2+O(g^3) $ with $g=2ζ-1 $. For a probe field with quartic self-interaction, we show that no nontrivial spherical static solution exists for $ζ\leq1/2 $ and derive local branch expansions near the s-wave thresholds. Numerical evolutions are consistent with saturation on the nodeless branch. These nonlinear results refer to the probe-field model; they do not establish the existence or stability of fully backreacted scalarized wormholes.

gr-qc↗

arXiv2026

Holonomy classification, gyroscope precession, and Landau levels in Gödel-type spacetimes and their superfluid analog

We derive the parallel-transport holonomies of circles centered on the symmetry axis in the homogeneous Gödel-type family of Rebouças and Tiomno, which includes the Gödel universe, the causal member with $m^2=4Ω^2$, and the Som--Raychaudhuri limit. The holonomy is governed by a single invariant $Δ(r)$, whose sign determines whether the Lorentz transformation is elliptic, parabolic, or hyperbolic. We determine the number of parabolic radii across the family and prove that, whenever the azimuthal circles become closed timelike curves (CTCs), the chronology radius satisfies $Δ(r_c)=-\cosh(mr_c)<0$. We also express this invariant in terms of Killing-vector scalars, derive the vector and spinor Wilson loops, give the exact condition for trivial holonomy after a finite number of turns, and analyze Fermi--Walker transport on circular CTCs. Finally, we discuss an analogy with the effective metric of a rotating superfluid, valid under stated conditions, and derive exact expressions for the radial $L^2$ localization of Klein--Gordon Landau modes relative to the Som--Raychaudhuri chronology radius. The geometric results are exact within the metric family considered; the discussion of the analog system relies on the validity of a coarse-grained effective description.

gr-qc↗

arXiv2026

Magnetic localization and spectral asymmetry of a charged particle at a screw dislocation

We study a charged particle moving outside a spiral (screw) dislocation in a uniform magnetic field. Although the geometry is locally Euclidean, its global screw identification couples the conserved axial and azimuthal quantities through the combination $\mathcal{J}=\ell-βk$ After eliminating the cyclic coordinates, the radial motion is governed by an inverse-square term determined by $\mathcal{J}$ and a harmonic confining term generated by the magnetic field. The corresponding reduced quantum problem is exactly solvable for $q\mathcal{B}_0\neq0$, yielding an equally spaced spectrum with an orientation-dependent energy shift. The radial probability density depends on $\mathcal{J}$, and opposite values of the screw-modified quantum number have identical spatial profiles but different energies for a fixed magnetic-field orientation. The radial size scales as $\sqrt{\langle r^2\rangle_n}\propto |q\mathcal{B}_0|^{-1/2}$, with the magnetic length setting the localization scale. At $q\mathcal{B}_0=0$, the confining term vanishes, and the problem reduces to a scale-free inverse-square system. Thus, the screw parameter enters the dynamics through the global coupling of the conserved axial and azimuthal quantities, whereas the magnetic field provides radial confinement and its orientation determines the spectral asymmetry.

cond-mat.mes-hall↗

arXiv2026

Hardware-aware quantum attention for fast radio burst identification

Fast radio bursts (FRBs) are millisecond-duration extragalactic pulses whose discovery requires searches over large signal-parameter spaces and the rejection of candidate sets dominated by radio-frequency interference and noise. Integrating quantum processors into FRB searches requires a workflow connecting telescop data to hardware-compatible models. Here we develop a pipeline that converts raw search-mode PSRFITS data into dynamic-spectrum segments and identifies FRB-like signals using a hybrid Quantum Vision Transformer (QViT). On labelled FAST data, the selected QViT achieves a mean accuracy of 94.00% and recall of 98.30%, with similar performance to a compact classical Vision Transformer. Recall reaches 97.11% on an FRB source excluded from training and model selection. Real-device execution on 82 segments yields a mean simulator-hardware Hellinger fidelity of 0.9161 +/- 0.0074. The workflow connects raw telescope data to quantum-assisted identification and provides an experimental basis for assessing the measurement requirements that must be addressed before survey-scale deployment.

astro-ph.HE↗

arXiv2024

Scaterring of Massless Quasiparticles in the 3He-A Superfluid

In this work, we analyze the scattering of fermionic quasiparticles in the presence of radial disgyrations and symmetric vortices in the superfluid 3He-A. We consider a Volovik analog model for the description of these defects and investigate the scattering of fermionic quasiparticles in this background. Furthermore, we solve the massless Dirac equation employing this methodology to gain comprehensive insights into the scattering phenomena and its dependence on the geometric properties. These results validate the optical theorem and highlight the role of defect topology in the scattering process.

cond-mat.mes-hall↗

arXiv2024

Redshift as a stretching factor in rotating graphene wormholes

In this paper, we discuss an extension of the geometric description of graphene wormholes in a non-inertial situation. We present an effective metric that describes the wormhole connection between two graphene sheets with matter content in rotation. Additionally, a stretching term as a function of the classical redshift of space has been found and discussed. We also explore the influence of a rotation term on quantum holonomy, recovering previous results found for the static case.

cond-mat.mes-hall↗

arXiv2021

Quantum Holonomy based in a Kaluza-Klein description for defects in $C_{60}$ fullerenes

In this paper, we discuss a new way to get a quantum holonomy around topological defects in $C_{60}$ fullerenes. For this, we use a Kaluza-Klein extra dimension approach. Furthermore, we discuss how an extra dimension could promote the formation of new freedom degrees which would open a discussion about a possible qubits computation.

cond-mat.mes-hall↗

arXiv2019

Analysis of the interaction of an electron with radial electric fields in the presence of a disclination

We consider an elastic medium with a disclination and investigate the topological effects on the interaction of a spinless electron with radial electric fields through the WKB (Wentzel, Kramers, Brillouin) approximation. We show how the centrifugal term of the radial equation must be modified due to the influence of the topological defect in order that the WKB approximation can be valid. Then, we search for bound states solutions from the interaction of a spinless electron with the electric field produced by this linear distribution of electric charges. In addition, we search for bound states solutions from the interaction of a spinless electron with radial electric field produced by uniform electric charge distribution inside a long non-conductor cylinder.

cond-mat.mes-hall↗

arXiv2018

Quantum Ring in Gapped Graphene Layer with Wedge Disclination in the Presence of an Uniform Magnetic Field

In this paper we investigate the relativistic quantum dynamics of a massive excitation in a graphene layer with a wedge disclination in the presence of an uniform magnetic field. We use a Dirac oscillator type coupling to introduce the confining potential for massive fermions in this system. We obtain the energy spectrum and eigenfunctions for the quantum ring pierced by Aharonov-Bohm flux resulting in appearance of persistent current and spontaneous magnetization.

cond-mat.mes-hall↗

arXiv2018

Landau Quantization for $ Λ$-Type Neutral Atoms in an Homogeneous Spin-Dependent Gauge Potential

We investigate the quantum dynamics of neutral atoms subject to a uniform spin-dependent gauge field. In particular, we analyze a simple experimental scheme to generate the Landau quantization in a two dimensional atomic gas with internal three-level $Λ$-type configuration. We show how energy eigenfunctions and eigenvalues are obtained and discuss the experimental conditions for which a variety of physical quantities of the atomic gas can exhibit quantum oscillations.

cond-mat.quant-gas↗

arXiv2017

Weyl fermions in a family of Gödel-type geometries with a topological defect

In this paper we study Weyl fermions in a family of Gödel-type geometries in Einstein general relativity. We also consider that these solutions are embedded in a topological defect background. We solve the Weyl equation and find the energy eigenvalues and eigenspinors for all three cases of Gödel-type geometries where a topological defect is passing through them. We show that the presence of a topological in these geometries contributes to modification of the spectrum of energy. The energy zero modes for all three cases of the Gödel geometries are discussed.

hep-th↗

arXiv2017

Magnetic oscillations for neutral atoms subject to an electromagnetic field

We show that the de Haas van Alphen effect can be induced in a two dimensional atomic gas by the He-McKellar-Wilkens interaction mediated via an electric dipole moment. Under an appropriate field-dipole configuration, we show that the neutral atoms subject to a synthetic magnetic field arrange themselves in Landau levels. An experimental arrangement for observation of the atomic analog of dHvA oscillations is proposed. In a strong effective magnetic field regime we present the quantum oscillations in the energy and effective magnetization of the two dimensional atomic gas. From the dHvA period we determine the area of the Fermi circle of the atomic cloud.

cond-mat.quant-gas↗

arXiv2017

Gap dependent mass of photon in photonic topological insulator

By using an analogy with axionic like systems, we study light propagation in periodic photonic topological insulator (PTI). The main result of this paper is an explicit expression for the PTI band structure. More specifically, it was found that for nonzero values of the topological phase difference $γ=θ_2-θ_1$ a finite gap $δ\proptoγ^2$ opens in the spectrum which is equivalent to appearance of nonzero effective photon mass $m^{*}(δ)\propto \frac{\sqrtδ}{δ+2}$.

cond-mat.mes-hall↗

arXiv2017

Dirac states in armchair- and zigzag-edged graphene Möbius strips

Edge structure plays an essential role in the nature of electronic states in graphene nanoribbons. By focusing on the interplay between this feature and non-trivial topology in the domain of the Dirac confinement problem, this paper proposes to examine how effects associated with edge shape manifest themselves in conjunction with the topological signature typical of Möbius strips within a low-energy regime. Aiming to provide an alternative to prevailing tight-binding approaches, zigzag and armchair Möbius strips are modeled by proposing compatible sets of boundary conditions, prescribing profiles of terminations in both transverse and longitudinal directions which are demonstrated to be coherent in describing consistently transverse edge patterns in combination with a proper Möbius periodicity. Of particular importance is the absence of constraints on the solution, in contrast with infinite mass analogues, as well as an energy spectrum with a characteristic dual structure responding exclusively to the parity associated with the transverse quantum number. Zigzag ribbons are predicted to possess an intrinsic mechanism for parity inversion, while the armchair ones carry the possibility of a coexistent gapless and gapped band structure. We also inspect the influence of the edge structure on persistent currents. In zigzag-edged configurations they are found to be sensitive to a length-dependent term which behaves as an effective flux. Armchair rings show a quite distinctive property: alternation of constant and flux-dependent currents according to the width of the ring, for a fixed transverse quantum number. In the flux-free case the effects of topology are found to be entirely suppressed, and conventional odd and even currents become undistinguishable.

cond-mat.mes-hall↗

arXiv2016

Two-Dimensional Quantum ring in a Graphene Layer in the presence of a Aharonov-Bohm flux

In this paper we study the relativistic quantum dynamics of a massless fermion confined in a quantum ring. We use a model of confining potential and introduce the interaction via Dirac oscillator coupling, which provides ring confinement for massless Dirac fermions. We obtain the energy levels and corresponding eigenfuctions for this model in graphene layer in the presence of Aharonov-Bohm flux in the centre of the ring and the expression for persistent current in this model. We also investigate the model for quantum ring in graphene layer in the presence of disclination and magnetic flux. The energy spectrum and wave function are obtained exactly for this case. We see that the persistent current depends in parameters characterizing the topological defect.

cond-mat.mes-hall↗

arXiv2016

de Haas van Alphen oscillations for neutral atoms in electric fields

In this work we study the de Haas van Alfhen (dHvA) effect for neutral atoms with a nonvanishing magnetic moment interacting with an electric field. Considering the particles confined in a two dimensional (2D) atomic cloud and using the Landau-Aharonov-Casher (LAC) theory, we obtain the effective magnetic field as well as the energy eigenfunctions and eigenvalues of the system. Assuming the neutral atoms as being $ ^{87}\mathrm{Rb} $ ultracold Rydberg atoms we calculate the degeneracy of the energy levels. Under a strong effective magnetic field regime we present the quantum oscillations in the energy and effective magnetization of the atomic gas. From the dHvA period we determine the area of the Fermi circle of the atomic cloud.

quant-ph↗

arXiv2016

Klein-Gordon Oscillator in Kaluza-Klein Theory

In this contribution we study the Klein-Gordon oscillator on the curved background within the Kaluza-Klein theory. The problem of interaction between particles coupled harmonically with a topological defects in Kaluza-Klein theory is studied. We consider a series of topological defects, that treat the Klein-Gordon oscillator coupled to this background and find the energy levels and corresponding eigenfunctions in these cases. We show that the energy levels depend on the global parameters characterizing these spacetimes. We also investigate a quantum particle described by the Klein-Gordon oscillator interacting with a cosmic dislocation in Som-Raychaudhuri spacetime in the presence of homogeneous magnetic field in a Kaluza-Klein theory. In this case, the spectrum of energy is determined, and we observe that these energy levels are the sum of the term related with Aharonov-Bohm flux and of the parameter associated to the rotation of the spacetime.

hep-th↗

arXiv2016

Description for rotating $C_{60}$ fullerenes via Gödel-type metric

In this contribution a geometric approach to describe a rotating fullerene molecule with Ih symmetry is developed. We analyze the quantum dynamics of quasiparticles in continuum limit considering a description of fullerene in a spherical solution of the Gödel-type space-time with a topological defect. As a result, we study the molecule in a rotating frame. Also we combine the well know non-Abelian monopole approach with this geometric description, including the case of the presence of the external Aharonov-Bohm flux. The energy levels and the persistent current for this study are obtained, and we show that they depend on the geometrical and topological properties of the fullerene. Also, we verify recovering of the well known results for limiting cases.

quant-ph↗