arXiv subjects

L. G. Barbosa

Publications and source records attributed to L. G. Barbosa.

10 recordsLinked to original sources

arXiv2026

Chiral symmetry and curvature bounds in de Sitter spacetime

We study chiral symmetry breaking in the Nambu-Jona-Lasinio model on a de Sitter background, treating it as a non-renormalizable effective field theory with a physical ultraviolet cutoff. Using exponential proper-time regularization, we obtain an exact solution for the constituent fermion mass in the strong-curvature regime via the Lambert $W$ function. The consistency condition for real-valued solutions leads to an upper bound on the cosmological constant, indicating a limitation of the mean-field description rather than a fundamental physical constraint on the spacetime geometry.

hep-th↗

arXiv2026

Black string immersed in perfect fluid dark matter

We present an exact four-dimensional black string solution immersed in perfect fluid dark matter within an anti-de Sitter background. By solving the Einstein field equations for an anisotropic fluid, we obtain a metric function that modifies the standard black string geometry through a logarithmic term governed by the dark matter parameter $α$. The event horizon radii are analytically determined using the Lambert $W$ function, and the Kretschmann scalar confirms a genuine curvature singularity at the origin alongside the expected asymptotic behavior. Furthermore, we evaluate the thermodynamic properties of the solution. The heat capacity diverges at a critical horizon radius for $α>0$, a behavior commonly associated with a thermodynamic phase transition in a regime where the weak energy condition is violated.

gr-qc↗

arXiv2026

Thermodynamics and quasinormal modes of the regular Dymnikova-Letelier black hole

In this work, we investigate the thermodynamic properties and quasinormal modes of a regular Dymnikova-Letelier black hole. Starting from the Einstein field equations sourced by an effective anisotropic fluid, we analyze the resulting spacetime geometry and derive the associated thermodynamic quantities, including the Hawking temperature, heat capacity, and Gibbs free energy. The thermodynamic analysis reveals the existence of phase transitions characterized by divergences in the heat capacity, whose location depends sensitively on the string fluid parameter. We then study the dynamical response of the system under scalar perturbations by computing the quasinormal mode spectrum using the sixth-order WKB approximation. Our results show that, for all considered values of the parameters, the imaginary part of the quasinormal frequencies remains negative, while the real part stays positive, indicating the stability of the black hole under scalar perturbations. Furthermore, the presence of the string fluid leads to systematic shifts in both the oscillation frequencies and damping rates. These results demonstrate that the string fluid significantly affects both the thermodynamic behavior and the dynamical stability of the Dymnikova-Letelier spacetime.

gr-qc↗

arXiv2026

Kiselev black strings in $f(R,T)$ gravity

In this work, we investigate exact black string solutions in the context of $f(R,T)$ gravity. Adopting the specific form $f(R,T) = R + 2χT$, we consider an anisotropic Kiselev fluid as the matter content and obtain static cylindrical solutions, which are then extended to the rotating case through a suitable coordinate transformation. The influence of the quintessence state parameter $w_q$ and the matter--geometry coupling constant $χ$ on the geometry is analyzed. We examine the weak, null, and strong energy conditions, identifying the regions in the parameter space where they are satisfied. Furthermore, we apply the Hamilton--Jacobi method to study the tunneling of scalar particles across the event horizon and derive the corresponding Hawking temperature. The thermodynamic stability of the solutions is investigated by computing the heat capacity, and the conditions for phase transitions are discussed. The results provide a characterization of black strings in $f(R,T)$ gravity surrounded by quintessence, highlighting the combined effects of anisotropic matter and modified gravity on their physical properties.

gr-qc↗

arXiv2026

Scalar Bosons with Coulomb Potentials in a Space with Dual Topological Defects in Rainbow Gravity

This work studies the relativistic quantum dynamics of scalar bosons in a spacetime containing both a cosmic string and a global monopole within the framework of Rainbow Gravity. An effective metric is constructed to describe the combined topological defects together with the energy-dependent deformation of spacetime. The Klein-Gordon equation is formulated in this background, including scalar, vector, and nonminimal couplings, and its solutions are obtained by separation of variables. Generalized Coulomb-type interactions are considered, allowing a unified analysis of scattering and bound states. The bound-state spectrum is determined from the poles of the corresponding $S$-matrix. Two specific choices of rainbow functions are examined, and their influence on the energy spectrum is analyzed through numerical calculations and, in suitable limits, analytical approximations. The results show how the interplay between topological defects and rainbow gravity corrections affects the spectral properties of scalar bosons, while known results are consistently recovered in appropriate limits.

gr-qc↗

arXiv2025

Charged scalar boson in Melvin universe

This work investigates the dynamics of a charged scalar boson in the Melvin universe by solving the Klein-Gordon equation with minimal coupling in both inertial and non-inertial frames. Non-inertial effects are introduced through a rotating reference frame, resulting in a modified spacetime geometry and the appearance of a critical radius that limits the radial domain of the field. Analytical solutions are obtained under appropriate approximations, and the corresponding energy spectra are derived. The results indicate that both the magnetic field and non-inertial effects modify the energy levels, with additional contributions depending on the coupling between the rotation parameter and the quantum numbers. A numerical analysis is also presented, illustrating the behavior of the solutions for two characteristic magnetic field scales: one that may be considered extreme, of the order of the ones proposed to be produced in heavy-ion collisions and another near the Planck scale.

gr-qc↗

arXiv2025

Cornell and Coulomb potentials in the double defect spacetime

We analyze the quantum dynamics of a scalar field in a spacetime incorporating dual topological defects, specifically a cosmic string and a global monopole. Utilizing a generalized metric that encapsulates the combined geometric effects of both defects, we solve the Klein--Gordon equation through separation of variables and examine the role of external potentials, with a focus on the generalized Cornell potential. A comparative analysis against the pure Coulomb potential is conducted to elucidate the modifications induced by the additional linear term. The presence of topological defects deforms the radial components of the wave equation, leading to energy spectrum shifts in bound states and alterations in scattering phase shifts. The results obtained provide a deeper theoretical foundation for understanding the behavior of spin-0 particles in nontrivial spacetime geometries, particularly in the presence of distinct potential interactions.

gr-qc↗

arXiv2025

Bound and Scattering States in a Spacetime with Dual Topological Defects: Cosmic String and Global Monopole

This paper explores the relativistic quantum motion of scalar bosons in the presence of mixed topological defects: cosmic strings and global monopoles. The Klein-Gordon equation with generalized Coulomb potentials is analyzed in this background. The effects of these topological defects on the equations of motion, phase shifts, and the S-matrix are examined in detail. Bound state solutions are derived from the poles of the S-matrix. We provide analytical expressions for the energy spectrum of bound states, with particular attention to how the parameters of scalar and vector potentials affect the behavior of the system. Furthermore, we explore particular cases involving pure scalar, vector, and mixed scalar-vector potentials, showing how these scenarios impose particular conditions on the existence of bound states. Our results indicate that the solutions obtained associated with scattering and bound states depend significantly on the parameters of the topological defects.

gr-qc↗

arXiv2025

Scalar bosons in Bonnor-Melvin-$Λ$ universe: Exact solution, Landau levels and Coulomb-like potential

In this work, we study spin-0 particles in a spacetime whose structure is determined by a homogeneous magnetic field and a cosmological constant. For this purpose, we take into account a framework based on the Bonnor-Melvin solution with the inclusion of the cosmological constant. We write the Klein-Gordon equation, solve it, and determine the Landau levels. The effects of scalar and vector potentials are considered, and we investigate the influence of the parameters of the theory on the results, which present observable effects. The implications of the physics of a stellar model based on this framework are also discussed.

gr-qc↗

arXiv2024

Klein-Gordon oscillator subject to a Coulomb-type potential in Bonnor-Melvin universe with a cosmological constant

In this work we study spin-0 particles described by the Klein-Gordon oscillator formalism in a spacetime which structure is determined by a homogeneous magnetic field and a cosmological constant. For this purpose we take into account a framework based on the Bonnor-Melvin solution with the inclusion of the cosmological constant. We write and solve the Klein-Gordon equation, and then find the energy spectrum by considering the effect of vector and scalar potentials.

gr-qc↗