arXiv subjects

Leonardo G. Barbosa

Publications and source records attributed to Leonardo G. Barbosa.

5 recordsLinked to original sources

arXiv2026

Regular fluid of strings black hole with non trivial core and asymptotic structure by gravitational decoupling

Cloud-of-strings (CS) geometries provide an effective description of one-dimensional string distributions. However, their central singularity cannot be removed through the standard regular black holes (RBH) mechanism based on an effective mass function, since the string sector contributes independently to the ultraviolet structure of the spacetime. Motivated by this observation, we investigate whether string-supported black holes can be consistently regularized while preserving the CS asymptotics and admitting a physically meaningful string-fluid interpretation. Using the gravitational decoupling method, we construct a RBH supported by an effective anisotropic string fluid. We show that the string sector deforms the de Sitter core, modifies the local topology of the spacelike slices, and introduces a longer-range correction dominating the usual Hayward/LQG term. The geometry admits non-extremal and extremal RBH, as well as a regular horizonless compact object. Moreover, the string parameter qualitatively modifies the thermodynamic evolution by shifting the Davies phase transition and the size of the black-hole remnant. Finally, the scalar quasinormal-mode spectrum exhibits systematic changes in both the oscillation frequencies and damping rates. These results show that regularizing string supported black holes is a physically distinct problem, with the matter sector governing the ultraviolet structure, thermodynamics, and dynamical response of the spacetime.

gr-qc↗

arXiv2026

Vacuum polarization in the Schwarzschild black hole with a global monopole

We investigate vacuum polarization on the event horizon of a Schwarzschild black hole carrying a global monopole. For a massless scalar field $Ψ$ in the Hartle-Hawking state and with arbitrary curvature coupling, we compute the renormalized vacuum expectation value $\langle Ψ^2 \rangle_{\textrm{ren}}$. The monopole produces a solid-angle deficit and makes the spacetime non-Ricci-flat. Working perturbatively in the monopole parameter $η$ and retaining terms through $O(η^2)$, we find that $\langle Ψ^2 \rangle_{\textrm{ren}}$ on the horizon splits into two contributions: a genuinely monopole-induced term evaluated at the horizon and the usual Schwarzschild result--with the event horizon radius modified by the presence of $η$. We also investigate whether an analogous decomposition holds for $\langle T^μ_{\phantomμμ}\rangle_\textrm{ren}$ when it is determined by this method. Our result parallels earlier analyses of Schwarzschild black holes pierced by a cosmic string.

gr-qc↗

arXiv2026

Charged black string immersed in a quintessence fluid and string cloud

We present a new static solution describing a charged black string immersed in a Kiselev-type quintessence fluid and a cloud of strings. The metric and field equations are solved for a general quintessence state parameter, with explicit results provided for the physically relevant case $w_q = -2/3$. We analyze the event-horizon structure and the Kretschmann scalar, verify energy-condition constraints, and derive thermodynamic properties including the Hawking temperature and heat capacity to identify stability regimes. Finally, we investigate the photon cylinder for null geodesics. The solution generalizes known charged black-string spacetimes by simultaneously including quintessence and a string-cloud parameter.

gr-qc↗

arXiv2025

Kiselev black strings: the charged rotating solutions

We investigate the properties of a charged rotating black string immersed in a Kiselev anisotropic fluid in anti-de Sitter (AdS) spacetime. The Einstein-Maxwell equations with an anisotropic stress-energy tensor and cosmological constant are analyzed and solved exactly. In this work, we calculate the Kretschmann scalar, obtaining a consistent result that agrees with the existing literature in the absence of charge and fluid. The rotating solution is obtained by applying a coordinate transformation on time and angular coordinates. The event horizon associated with specific values of the equation of state parameter $w_q$ is studied. The results show an important influence of the fluid parameters $N_{q}$ and $w_{q}$, the charge parameter $Q$, and the rotation parameter $a$ on the size of the black string horizon. In addition, we determine the conditions for the existence of closed timelike curves (CTCs) and compute the conserved charges, such as mass, angular momentum, and electric charge of the black string. Utilizing the Klein-Gordon equation, we employ the quantum particle tunneling approach to obtain the probability of charged scalar particles tunneling across the event horizon. We obtain the correspondent Hawking temperature as a consequence. Furthermore, we examine the thermodynamic properties, including entropy and heat capacity, to assess the effects of the quintessence field and charge on the black string. The results include particular cases such as the Lemos black string, providing a broader view of black string configurations in AdS spacetime.

gr-qc↗

arXiv2025

Black Strings and String Clouds Embedded in Anisotropic Quintessence: Solutions for Scalar Particles and Implications

We analyze the spacetime metric associated with a black string surrounded by a cloud of strings and an anisotropic fluid of quintessence in cylindrically symmetric AdS spacetime. We solve Einstein's equation to obtain the explicit form of the metric, investigate typical values for its parameters, and determine their role in the event horizon formation. Within our findings, we show that the intensity of the cloud of strings regulates the size of the event horizon and, when the cloud is absent, the horizon increases drastically for larger values of the quintessence's state parameter $α_{Q}$. Additionally, the metric shows that, unless $α_{Q}$ is close to its lower bound, the contribution from the quintessence fluid is only significant at large distances from the black string. Finally, to explore the quantum implications of this dark energy candidate, we use the confluent Heun function to solve the Klein-Gordon equation for a spin-0 particle near the event horizon. Our results indicate that the presence of quintessence alters the particle's radial wave function. This modification, in principle, could give rise to an observable that we termed as \enquote{dark phase}.

gr-qc↗