arXiv subjects

Edilberto O. Silva

Publications and source records attributed to Edilberto O. Silva.

At least 37 records · Page 2Linked to original sources

arXiv2026

Thermodynamics and emergent thermomechanical response of a quantum ring with nonminimal spin--orbit coupling

We investigate the thermodynamic and emergent thermomechanical properties of fermions confined to a one-dimensional quantum ring with effective spin--orbit interactions induced by nonminimal couplings to antisymmetric tensor fields. Using the exact spectrum obtained in the companion work, we develop canonical and grand-canonical descriptions and show that the coupling parameter~$ξ$ deforms the angular-momentum branches, reorganizing the low-energy spectrum and leaving clear signatures in the internal energy, entropy, heat capacity, and spin--orbit response functions. We also formulate an effective thermomechanical description by treating the ring circumference as a quasi-static thermodynamic variable. This leads to a pressure-like quantity and associated response coefficients, directly linked to the microscopic spectrum. In the grand-canonical ensemble, Fermi statistics strongly enhance the response, producing coupling-dependent instabilities and sign changes reminiscent of mesoscopic de~Haas--van Alphen oscillations. Finally, we introduce a phenomenological interacting extension based on an exponential resummation of the free energy, showing that collective effects can sharpen the thermomechanical response and induce anomalous thermal contraction. Our results connect spectral deformation, finite-size thermodynamics, and emergent mechanical behavior in spin--orbit-active quantum rings.

cond-mat.stat-mech↗

arXiv2026

Hawking Temperature, Sparsity and Energy Emission Rate of Regular Black Holes Supported by Primordial Dark Matter

In this paper, we investigate the thermodynamic and radiative properties of a regular black hole sourced by primordial dark matter (PDM), modeled effectively through a Dirac--Born--Infeld (DBI) scalar field. We compute the Hawking temperature, the entropy obtained from the first law at fixed PDM scale, the specific heat capacity, the sparsity parameter of the Hawking flux, and the spectral energy emission rate. Particular attention is devoted to the role played by the regularity scale parameter $α$ and to the recovery of the Schwarzschild limit. Using the normalization in which the integration constant $M$ is the ADM mass and $f(r)=1-2M/r+\mathcal{O}(r^{-3})$, we find that the PDM scale suppresses the Hawking temperature and the spectral energy emission rate relative to the Schwarzschild case. The fixed-$α$ heat capacity remains negative along the physical branch, indicating the persistence of local thermodynamic instability in the canonical ensemble. Moreover, within the effective-area prescription adopted here, the geometrical sparsity parameter receives a negative leading correction in the perturbative regime $α\ll 2M$, implying a slight reduction of the intermittency of the Hawking flux. We also distinguish between the near-horizon geometrical estimate and the shadow-based high-energy absorption cross-section used in the emission rate.

gr-qc↗

arXiv2026

Perturbations and greybody bounds of Euler-Heisenberg black holes surrounded by perfect fluid dark matter

We investigate the propagation of massless fields with spins $s=0$, $s=1$, and $s=1/2$ in the spacetime of an Euler-Heisenberg (EH) black hole surrounded by perfect fluid dark matter (PFDM). This background incorporates both the nonlinear electrodynamic correction associated with the EH effective theory and the logarithmic contribution induced by the surrounding dark matter distribution. After deriving the corresponding Schrödinger-like radial equations, we construct the effective potentials for scalar, electromagnetic, and Dirac perturbations and analyze how they are modified by the black hole charge, the EH parameter, and the PFDM parameter. The greybody factors are estimated through the rigorous Boonserm-Visser lower-bound method, and the associated partial absorption cross sections are obtained for different spin sectors using these bounds. Our results show that the nonlinear electrodynamic and dark matter parameters significantly deform the effective potential barrier, leading to potentially distinguishable changes in the transmission probabilities and absorption spectra within the model. In particular, the greybody lower bounds increase monotonically with the frequency and approach the high-frequency limit, while their low-frequency behavior is strongly affected by the geometry and by the spin of the perturbing field. Moreover, we utilize the greybody lower bound to calculate the energy emission rate. Finally, we make comparisons with the Schwarzschild, Reissner-Nordström, and pure EH limits, showing that the combined EH+PFDM background produces distinguishable corrections to black-hole scattering within the model. These results highlight greybody bounds as sensitive diagnostic probes of nonlinear electrodynamic effects and dark matter halos around compact objects.

gr-qc↗

arXiv2026

Thermodynamic and Radiative Properties of Euler-Heisenberg AdS Black Holes Surrounded by Quintessence and Dark Matter with a Cloud of Strings

We investigate the thermodynamics, criticality, and selected radiative and optical properties of an Euler-Heisenberg AdS black hole surrounded by quintessence, perfect fluid dark matter, and a cloud of strings. Within the extended phase-space formalism, we derive the thermodynamic quantities, verify the modified first law and Smarr relation, and analyze the corresponding equation of state and critical behavior. We show that the Euler--Heisenberg coupling and the surrounding matter fields substantially modify the temperature profile, the stability structure, and the location of the critical point. We also examine the sparsity of Hawking radiation, together with the photon sphere, black hole shadow, and the associated geometric-optics emission rate.

gr-qc↗

arXiv2026

Hawking Temperature, Sparsity and Energy Emission Rate of Dark Matter Halo Regular Black Holes

In this paper, we investigate the thermodynamic and radiative properties of a regular black hole sourced by a dark matter halo described by the Einasto density profile. The closed-form expressions for the Hawking temperature, specific heat capacity, sparsity parameter of Hawking flux, and the spectral energy emission rate were obtained. All these are examined as a function of the characteristic scale parameter $α$ of the dark matter distribution and compared with the standard Schwarzschild results. We show that the presence of a dark matter halo suppresses both the Hawking temperature and energy emission rate relative to the standard black hole result. Crucially, the specific heat capacity can be positive for a finite range of horizon radii, signaling a thermodynamically stable phase; the boundary of this stable region defines a Davies-type phase transition. The sparsity parameter is higher than in the standard black hole, indicating that the dark matter environment makes the Hawking flux even more intermittent.

gr-qc↗

arXiv2026

Shadow, Quasinormal Modes, Sparsity, and Energy Emission Rate of Euler-Heisenberg Black Hole Surrounded by Perfect Fluid Dark Matter

In this work, we investigate the optical, dynamical, and radiative properties of an Euler--Heisenberg black hole immersed in a perfect fluid dark matter (PFDM) background. We analyze the photon sphere and shadow, the scalar quasinormal-mode spectrum in the eikonal regime, the grey-body factor through the eikonal QNM correspondence, the sparsity of Hawking radiation, and the corresponding energy emission rate. Our results show that both the black-hole charge and the PFDM parameter significantly affect the photon sphere, shadow size, quasinormal frequencies, Hawking temperature, and emission profile, whereas the Euler--Heisenberg correction is typically subleading in the parameter range explored, although it may become more visible in strong-charge regimes for selected observables. Overall, the dark-matter environment provides the dominant imprint on the phenomenology of the system, indicating that shadow and ringdown-related quantities may serve as useful probes of PFDM effects within the approximations considered.

gr-qc↗

arXiv2026

Charged Black Holes in KR-gravity Surrounded by Perfect Fluid Dark Matter

In this work, we systematically investigate the null geodesics of electrically charged black holes in a gravitational framework that incorporates Lorentz violation induced by a background Kalb-Ramond (KR) field, in the presence of perfect-fluid dark matter. The properties of the photon sphere, black hole shadow, and photon trajectories are analyzed in detail. Furthermore, to explore the combined effects of Lorentz violation and dark matter on the motion of neutral test particles, we examine the innermost stable circular orbit (ISCO) in this spacetime. In addition, the epicyclic frequencies of test particles are studied to gain further insight into the dynamical behavior of particle motion around these black holes. The main analytical results are complemented by a phenomenological QPO analysis, a thermodynamic investigation, and a discussion of the sparsity of Hawking radiation, allowing us to connect optical, dynamical, and thermodynamic signatures within a single framework.

gr-qc↗

arXiv2026

Geometric Phases and Persistent Spin Currents from nonminimal couplings

We investigate a class of nonminimal derivative couplings between fermions and electromagnetic fields that generate Rashba-like spin--orbit interactions in one-dimensional quantum rings. Starting from a generalized Dirac Lagrangian containing two independent axial structures built from the field strength $F_{μν}$ and its dual $\tilde{F}_{μν}$, we perform a systematic nonrelativistic expansion and show that both couplings induce effective Hamiltonians of the form $\boldsymbol{\mathcal{F}}\cdot(\boldsymbol{p}\times\boldsymbolσ)$. This reveals that magnetic as well as electric background fields may give rise to Rashba-type interactions, in contrast with standard condensed-matter scenarios. Before passing to the nonrelativistic limit, we analyze the relativistic content of the model in detail: the canonical structure of the deformed Dirac operator, the admissible background classes, the effective bilinear current, and the branch splitting of the relativistic dispersion relation, which constitutes the primary relativistic signature of the theory. We derive exact analytical energy levels and normalized eigenspinors for the resulting ring Hamiltonian, compute Aharonov--Anandan geometric phases, and analyze persistent spin currents together with the associated differential spin response $\mathcal{G}_s = \partial\mathcal{J}_φ^z/\partialξ$. Exploiting the analytical control offered by the model, we derive the first systematic order-of-magnitude bounds on the two Lorentz-invariant couplings $\mathfrak{g}_1$ and $\mathfrak{g}_2$ from both spectroscopic and mesoscopic scenarios, identifying the experimental channels most sensitive to the new physics encoded in these operators. We discuss physical implications, signatures, and possible experimental analogs, and outline several promising directions involving disorder, noise, and nonequilibrium spin dynamics.

hep-th↗

arXiv2026

Thermodynamics and orbital structure of anti-de Sitter black holes in Palatini-inspired nonlinear electrodynamics

We construct a consistent anti-de Sitter completion of the static and spherically symmetric black-hole solution sourced by the Palatini-inspired nonlinear electrodynamics $Y^n$ model. Starting from the Einstein--Hilbert action with a negative cosmological constant and the first-order PINLED sector, we derive the full set of field equations and show that the nonlinear electromagnetic solution preserves its original parametric structure, while the lapse function acquires the standard AdS contribution. We then analyze the horizon structure, Hawking temperature, extended phase-space thermodynamics, and the associated equation of state. In addition, we investigate null and timelike geodesics, with emphasis on the effective potentials, photon sphere, shadow radius for a static observer at finite distance, and innermost stable circular orbit. The resulting framework furnishes the exact AdS extension of the asymptotically flat PINLED black hole and provides a coherent basis for numerical and phenomenological studies of its thermodynamic, optical, and orbital properties.

gr-qc↗

arXiv2026

Charged Black Holes in Bumblebee gravity with Global Monopole: Thermodynamics and Shadow

In this paper, we perform a detailed study of the thermodynamic properties of a charged black hole in bumblebee gravity in the presence of a global monopole. We also analyze the optical characteristics of this black hole solution, highlighting the influence of Lorentz symmetry violation and the global monopole on the black hole shadow. Furthermore, we examine the trajectories of both photons and test particles in this spacetime, showing how the geometric parameters alter their paths. Moreover, we study the dynamics of neutral test particles, with particular attention to the location of the innermost stable circular orbits (ISCOs). Finally, we investigate massless scalar perturbations and derive bounds on the greybody factors, illustrating how the black hole's geometric parameters affect field propagation, energy emission, and radiation sparsity in this background.

gr-qc↗

arXiv2026

Analytical Solutions of One-Dimensional ($1\mathcal{D}$) Potentials for Spin-0 Particles via the Feshbach-Villars Formalism

We present a unified analytical and numerical study of the one-dimensional Feshbach--Villars (FV) equation for spin-0 particles in the presence of several representative external potentials. Starting from the FV formulation of the Klein--Gordon equation, we derive the corresponding one-dimensional master equation and analyse its solutions for Coulomb, power-exponential, Cornell, Pöschl--Teller, and Woods--Saxon interactions. For the singular Coulomb and Cornell cases, a Loudon-type cutoff regularisation is implemented on the full line, allowing a mathematically controlled treatment of the origin and an explicit classification of the states by parity. The Coulomb problem exhibits the expected near-degenerate even--odd structure in the cutoff limit, while the Cornell potential combines short-distance Coulomb behaviour with long-distance confinement and produces a finite set of bound states for fixed parameters. The power-exponential potential with $p=1$ is reduced to a Whittaker-type equation and yields an intrinsically relativistic spectrum with no standard Schrödinger bound-state limit in the parameter regime considered. For the smooth short-range Pöschl--Teller and Woods-Saxon potentials, the FV formalism reveals, respectively, the effects of definite parity and spatial asymmetry on the spectrum, wave functions, and particle--antiparticle mixing. In all cases, we reconstruct the full FV spinor, analyse the associated charge density, and compare the relativistic behaviour with the corresponding non-relativistic expectations whenever such a limit exists. The results provide a coherent set of analytical and numerical benchmarks for relativistic scalar bound states in one dimension.

quant-ph↗

arXiv2026

Structured-light propagation in a medium with uniform torsion: polarization textures, geometric birefringence, and beam-resolved optical activity

We investigate finite-width optical-beam propagation in a medium with uniform torsion described by the geometric theory of a continuous distribution of screw dislocations. Starting from the Riemann--Cartan framework that yields torsion-induced circular birefringence for local plane waves, we construct a minimal paraxial beam model in which the same contortion-driven helicity splitting remains explicit. We show that uniform torsion breaks the degeneracy between the two circular-polarization sectors and induces a geometric rotation of the polarization that scales with both the propagation distance and the radial position in the beam. As a consequence, a finite-width beam develops spatially varying polarization textures across its transverse profile, naturally described by the Stokes parameters. We introduce beam-level observables based on the integrated Stokes vector, the transverse inhomogeneity of the polarization texture, and the number of resolved radial polarization domains, thereby connecting the torsion parameter to experimentally accessible beam diagnostics. The paper combines two complementary levels of description: an analytic short-distance regime, used to isolate the geometric mechanism, and full paraxial propagation including diffraction, used to test the robustness of the predicted textures. Within the cylindrically symmetric minimal model, the most robust structured-light signature of uniform torsion is beam-resolved polarization structuring, whereas strong orbital-angular-momentum conversion is not expected without additional azimuthal structure. We also identify the geometric ingredient required for genuine torsion-assisted spin--orbit conversion beyond the minimal radial model: an effective azimuthal geometric connection.

physics.optics↗

arXiv2026

Thermodynamic Analysis of Charged AdS Black Holes with Cloud of Strings in Einstein-Bumblebee Gravity via Tsallis Entropy

We investigate the thermodynamic properties of charged anti-de Sitter black holes surrounded by a cloud of strings in bumblebee gravity. In this framework, the cloud-of-strings parameter $α$ and the Lorentz-violating parameter $\ell$ modify the horizon structure, the Hawking temperature, the free energies, the specific heat, and the critical behavior in the extended phase-space description. We derive the corresponding equation of state and show that the system exhibits a small--large black-hole phase transition of Van der Waals type. In particular, the critical quantities are deformed by both the cloud of strings and the bumblebee background, while the universal ratio is explicitly altered by Lorentz symmetry breaking. We also examine the Joule--Thomson expansion and analyze the associated inversion and isenthalpic curves, showing how the deformation parameters shift the boundary between heating and cooling regions. In addition, we extend the thermodynamic analysis to a Tsallis entropy-based framework and show that the non-extensive parameter $δ$ significantly changes the temperature profile, stability windows, critical volume, free energies, and sparsity of Hawking radiation. Our results reveal that the combined effects of the string cloud, Lorentz violation, and non-extensive entropy lead to a substantially richer thermodynamic structure than that of the standard Reissner--Nordström--AdS black hole.

gr-qc↗

arXiv2026

Screened Simpson-Visser Black Holes with Asymptotically de-Sitter Core

In this work, we introduce a screened Simpson-Visser regular solution and perform a comprehensive study of its physical and observational properties. We begin by analyzing the thermodynamic behavior of the black hole, including detailed investigations of the Hawking temperature, Gibbs free energy, and specific heat, which provide insights into its stability and phase structure. Next, we examine the geodesic structure of the spacetime, considering both massless (photon) and massive (timelike) particles. In particular, we study the photon sphere, the corresponding black hole shadow, and the innermost stable circular orbits (ISCO), which are crucial for understanding the motion of matter and light around the black hole. Furthermore, we explore the black hole's energy-emission rate radiation, highlighting the effects of the modified geometry on observational signatures. Finally, we investigate the topological aspects of the black hole, analyzing both the thermodynamic topology and the photon sphere's topological properties. Our analysis demonstrates the intricate interplay between the spacetime geometry, geodesic motion, and black hole thermodynamics, offering a deeper understanding of this class of regular black holes and their potential observational consequences.

gr-qc↗

arXiv2026

Dyonic ModMax Black Holes in Kalb-Ramond gravity with a Cloud of Strings as Source

We investigate the geodesic structure, shadow, thermodynamics, and Hawking radiation from a dyonic ModMax black hole in Kalb-Ramond gravity with a cloud of strings. The combined presence of ModMax nonlinear electrodynamics, the Lorentz-violating Kalb-Ramond background, and the string cloud breaks asymptotic flatness and introduces a global conical deficit that modifies all observables through a single geometric prefactor. We derive analytic expressions for the photon sphere, critical impact parameter, and shadow radius, and show that the shadow size depends on both the non-flat asymptotics and the ModMax screening of the dyonic charge. For massive test particles, we determine the innermost stable circular orbit and the accretion efficiency as functions of all model parameters. We also establish the first law of black hole thermodynamics and the generalized Smarr relation for this solution, identify a Hawking-Page-type phase transition in the specific heat, and compute the spectral energy emission rate, which we show is directly governed by the shadow radius in the geometric-optics limit. Our results demonstrate that the interplay of these three ingredients produces a phenomenology observationally distinguishable from standard Reissner-Nordström black holes.

gr-qc↗

arXiv2026

Accelerating Bertotti-Robinson Black Holes in a Uniform Magnetic Field

We study the Hawking temperature, geodesic motion, and observable signatures of the accelerating Bertotti-Robinson (BR) spacetime, a vacuum black-hole solution deformed by a uniform magnetic field $B$ and an acceleration parameter $α$. In the timelike sector, we derive the effective potential for massive particles, determine the specific energy and angular momentum for equatorial circular orbits, and determine how $(B,α)$ shifts the ISCO; we also illustrate representative trajectories of massive particles. We then compute the radial and latitudinal epicyclic frequencies for small perturbations about circular orbits, quantifying how the magnetic field and acceleration modify local radial and vertical stability. In the null sector, we derive the photon effective potential and obtain analytical expressions for the photon-sphere radius, critical impact parameter, and shadow radius, complemented by photon trajectories, the effective radial force, and the Lyapunov exponent controlling the instability of circular null orbits; we also provide parameter-space maps for the photon sphere and shadow. Finally, we obtain the energy emission rate emitted from the black hole, showing how the acceleration parameter and the magnetic field affect this.

gr-qc↗

arXiv2026

Magnetoresistance and electric current oscillations induced by geometry in a two-dimensional quantum ring

In this work, we investigate the effects of a controlled conical geometry on the electric charge transport through a two-dimensional quantum ring weakly coupled to both the emitter and the collector. These mesoscopic systems are known for being able to confine highly mobile electrons in a defined region of matter. In particular, we consider a GaAs device having an average radius of $800\hspace{0.05cm}\text{nm}$ in different regimes of subband occupation at non-zero temperature and under the influence of a weak and uniform background magnetic field. Using the adapted Landauer formula for the resonant tunneling and the energy eigenvalues, we explore how the modified surface affects the Van-Hove conductance singularities, the magnetoresistance interference patterns resulting from the Aharonov-Bohm oscillations of different frequencies and the charge transport when an electric potential is applied in the terminals of the device. Magnetoresistance and charge current oscillations depending only on the curvature intensity are reported, providing a new feature that represents an alternative way to optimize the transport through the device by tuning its geometry.

cond-mat.mes-hall↗

arXiv2026

Numerical study of non-relativistic quantum systems and small oscillations induced in a helically twisted geometry

We investigate bound states of a non-relativistic scalar particle in a three-dimensional helically twisted (torsional) geometry, considering both the free case and the presence of external radial interactions. The dynamics is described by the Schrödinger equation on a curved spatial background and, when included, by minimal coupling to a magnetic vector potential incorporating an Aharonov--Bohm flux. After separation of variables, the problem reduces to a one-dimensional radial eigenvalue equation governed by an effective potential that combines torsion-induced Coulomb-like and centrifugal-like structures with magnetic/flux-dependent terms and optional model interactions. Because closed-form analytic solutions are not reliable over the parameter ranges required for systematic scans, we compute spectra and eigenfunctions numerically by formulating the radial equation as a self-adjoint Sturm--Liouville problem and solving it with a finite-difference discretization on a truncated radial domain, with explicit convergence control. We analyze four representative scenarios: (i) no external potential, (ii) Cornell-type confinement, (iii) Kratzer-type interaction, and (iv) the small-oscillation regime around the minimum of a Morse potential. We present systematic trends of the low-lying levels as functions of the torsion parameter, magnetic field, and azimuthal sector, and we show that geometric couplings alone can produce effective confinement even in the absence of an external interaction.

quant-ph↗