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Francisco Tiago Barboza Sampaio

Publications and source records attributed to Francisco Tiago Barboza Sampaio.

2 recordsLinked to original sources

Traversable Hyperbolic Wormholes with a Casimir-Memory Source: Complexity and Shell-Free Matching

Hyperbolically symmetric wormholes provide a setting in which negative energy densities arise from the throat geometry and finite matter configurations can be matched to the hyperbolic Schwarzschild vacuum. We construct such configurations from a matter-first perspective using an effective Casimir source corrected by a gravitational-memory contribution, $ρ(r)=-α/r^4+η/r^7$. The $r^{-7}$ term is motivated by the persistent shift of the Casimir vacuum energy after a transient gravitational perturbation, while its promotion to a radial source is treated phenomenologically. The density determines the shape function, and the temporal geometry is fixed through complexity-based conditions. Full vanishing complexity, $Y_{TF}=0$, is first imposed and then relaxed through a one-parameter deformation, $Y_{TF}=(p-3)r_0/(2r^3)$. Decomposing the complexity factor into local and throat contributions shows that local vanishing complexity occurs at $p=β'(r_0)$. At this value, besides the constant-redshift solution of the finite-$r$-derivative branch, a second lapse branch is regular in radial distance. We show that pressure-free Darmois matching in the finite-$r$-derivative family requires $p<β'(r_0)$, enforcing tangential null and strong-energy-condition violations at the throat throughout the matching domain. The density remains negative in the matter-supported region, implying weak- and dominant-energy-condition violations independently of the lapse branch. The memory parameter modifies the flare-out domain, redshift profile, and matching data, while finite pressure-free junctions permit smooth matching to the hyperbolic Schwarzschild vacuum without thin shells. The construction combines a memory-corrected Casimir source with a unified complexity framework in which the temporal sectors emerge as related branches of the same radial geometry.

gr-qc↗

Regularized Black Hole Solution from a New String Cloud Source

We construct a new family of regular black hole solutions supported by the novel Letelier-Alencar string cloud and regularized through a rational Dagum-type distribution. The regulator smooths the matter profile and ensures finite curvature invariants, yielding a geometry that interpolates between a string-cloud exterior and an anti--de Sitter core. We analyze the energy conditions, identifying where the null, weak, dominant and strong conditions hold or fail across the core and exterior. The parameter space for horizon formation is mapped and the thermodynamic propertie -- mass, Hawking temperature, entropy and heat capacity -- are derived; notably, the entropy depends only on the regularization scale while the string parameter modifies temperature and heat capacity. Employing Rényi non-extensive entropy and the topological thermodynamics approach, we show the non-extensive deformation stabilizes the system and removes the standard phase transition. Finally, we compute the shadow radius and derive constraints compatible with current Event Horizon Telescope bounds for Sgr~A* and M87*.

gr-qc↗