arXiv subjects

Francisco Bento Lustosa

Publications and source records attributed to Francisco Bento Lustosa.

10 recordsLinked to original sources

arXiv2026

Traversable Wormholes Supported by Entropy-Inspired Effective Matter Sectors

The thermodynamic interpretation of gravity suggests that modifications of horizon entropy can be encoded in effective geometries and matter distributions. Motivated by the entropy--geometry correspondence, we investigate Morris--Thorne wormholes constructed from density profiles associated with Barrow, Tsallis, Kaniadakis, logarithmic, and exponential black-hole entropies. The wormhole construction retains each entropy-induced density as input to the shape-function equation, while the radial and tangential pressures are reconstructed independently from the wormhole field equations, a barotropic radial equation of state, anisotropic conservation, and throat regularity. Barrow and Tsallis yield algebraic negative-density distributions; Kaniadakis and exponential corrections produce localized profiles; and the logarithmic sector admits both negative-density and positive-density phantom-like regimes. For every regular configuration considered, radial null energy condition violation at the throat follows from the flare-out condition. Its areal-volume integral is finite and negative for every nonzero deformation: it becomes unbounded when the regular Barrow, Tsallis, and Kaniadakis branches approach their undeformed values, but remains finite in the logarithmic and exponential limits. Removing the density deformation also fails to commute with taking the infinite-radius limit in the Barrow, Tsallis, and Kaniadakis sectors, whereas the two operations agree for the logarithmic and exponential sectors in their pole-free domains. The selected entropy-induced densities can therefore be embedded consistently in traversable-wormhole reconstructions, with the pressure sector fixed by the wormhole geometry and the global source behavior controlling both the asymptotic mass and the integrated radial exoticity.

gr-qc↗

arXiv2026

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↗

arXiv2026

Traversable Casimir Wormholes with Gravitational Memory

We investigate a class of traversable wormhole geometries supported by an effective Casimir source corrected by gravitational memory. The construction is motivated by the fact that a time-dependent gravitational background can leave a permanent positive shift in the vacuum polarization of a quantum field confined to a Casimir cavity. By promoting the plate separation to an effective radial scale in the Morris-Thorne spacetime, we obtain a density profile composed of the usual negative Casimir contribution, proportional to $r^{-4}$, and a positive memory-induced correction, proportional to $r^{-7}$. The corresponding shape function is derived directly from the Einstein equations and satisfies the throat condition by construction. We determine the redshift function from a constant barotropic equation of state together with the requirement of regularity at the throat, which fixes the barotropic parameter in terms of the Casimir and memory coefficients. The flare-out condition defines the admissible range of the memory parameter and separates a Casimir-dominated sector from a phantom-like sector, with the transition point associated with a singular limit of the constant-barotropic description. We analyze the curvature scalar, the embedding structure, the energy conditions, and the Tolman-Oppenheimer-Volkoff equilibrium of the anisotropic matter source. The radial null energy condition is necessarily violated at the throat, while the tangential sector depends sensitively on the redshift gradient. We also examine the shadow radius as a phenomenological diagnostic and show that admissible solutions can overlap the EHT range for M87*. The results indicate that gravitational memory can deform Casimir-supported wormholes by softening the ordinary Casimir contribution, modifying the near-throat geometry, and reshaping the internal stress balance required to sustain traversability.

gr-qc↗

arXiv2025

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↗

arXiv2025

Black holes inside cosmic voids

This study examines the gravitational and thermodynamic properties of static, spherically symmetric black holes within cosmic voids -- vast underdense regions of the universe. By deriving a novel solution based on a universal density profile for voids, we analyze its spacetime structure, which reveals two horizons: One of the black hole and the other related to the de Sitter-like behavior. As the void approaches a perfect vacuum, the black hole horizon diminishes, tending to that of the Schwarzschild solution, while the outer horizon increases. We also study the solution stability via sound speed of the fluid, as well as the thermodynamic properties, including Hawking temperature, evaporation time, entropy, and specific heat. Our results show that as the void empties, the Hawking temperature rises, shortening evaporation times. The entropy follows the area's law and specific heat exhibits a minimum for a given black hole size, indicating a thermal transition and highlighting the role of voids in the black hole evolution. These findings offer new insights into the relationship between local gravitational collapse and large-scale cosmic structure, enhancing our understanding of the black hole behavior in underdense environments. We also provide a glimpse of a potential thermodynamic interaction between the event horizon and the cosmological horizon.

gr-qc↗

arXiv2025

Quantum improved wormholes in the Dekel-Zhao dark matter halo

This work presents and investigates novel traversable wormhole solutions within the framework of Asymptotically Safe Gravity (ASG), sourced by a dark matter halo modeled by the Dekel--Zhao density profile. The scale-dependent gravitational coupling $G(k)$, derived from the ASG renormalization group flow in the infrared regime, is incorporated directly into the field equations, providing a consistent description of quantum gravitational corrections even at astrophysical scales. The combined effects of the running coupling (parameterized by $ξ$) and the dark matter characteristics determine the geometric structure and physical viability of the wormhole. The solutions satisfy the flare-out and asymptotic flatness conditions within restricted parameter domains, exhibiting enhanced curvature near the throat due to ASG corrections. Null Energy Conditions are necessarily violated at the throat, and stability analysis based on the adiabatic sound speed as well as the modified Tolman--Oppenheimer--Volkoff equation reveal that quantum effects from ASG counteract the destabilizing influence of dark matter. Phenomenologically, the wormhole shadow radius increases nearly linearly with $ξ$, lying within the Event Horizon Telescope bounds for Sgr~A$^*$ when $ξ/M \simeq 0.8--0.9$, thus suggesting that ASG-corrected wormholes may represent observable signatures of quantum gravity in the strong-field regime.

gr-qc↗

arXiv2025

Einstein-Yang-Mills Regular Black Holes in Rainbow Gravity

In this work, we investigate regular black hole solutions in nonminimal Einstein-Yang-Mills theory modified by Rainbow Gravity, focusing on the impact of quantum gravity effects on their thermodynamics, particle emission, energy conditions, curvature, and shadow formation. We find that the rainbow parameter $λ$ alters Hawking's temperature, entropy, and specific heat, leading to modified phase transitions and the possible formation of remnants. We calculate the graybody factor demonstrating that particle emission is enhanced with increasing $λ$, reflecting the behavior of the temperature and confirming the impact of the rainbow parameter on the evaporation process. Energy conditions are violated inside the black hole, with violations intensifying for larger $λ$. We also show that Rainbow Gravity mitigates singularity formation by softening the curvature near the origin, contributing to the regularity of the solution. Finally, we study the black hole shadow and demonstrate that its radius decreases as quantum gravity effects strengthen, suggesting potential observational tests for Rainbow Gravity. These results highlight the role of Rainbow Gravity in modifying black hole physics and provides a framework for exploring quantum gravitational corrections in astrophysical scenarios.

gr-qc↗

arXiv2025

Dynamical analysis of quantum matter bounces with dark sector mimickers

We study the effects of the inclusion of fluids In bounce scenarios driven by an exponential potential scalar field. Most solutions exhibit well known tracking behavior between the fluids and the scalar field. This tracking behavior can model transitions between different phases of cosmic evolution. We will focus on an interesting bouncing model with a dust matter fluid, where the scalar field can drive an early dark energy expanding period with a radiation-like dominated phase just after it, and then tracks the dust matter fluid with energy density compatible with the dark matter energy density. The model is dust dominated in the far past of the contracting phase, and has stiff matter behavior when approaching the singularity, allowing well known quantum bounce transitions to the expanding era. Hence, it is a quantum matter bounce scenario with an inflationary phase together with a smooth transition through a radiation era to matter domination with a possible scalar field dark matter candidate.

gr-qc↗

arXiv2023

Evolution of Quantum Nonequilibrium for Coupled Harmonic Oscillators

In the context of de Broglie-Bohm pilot-wave theory, violations of the Born rule are allowed and can be considered as describing nonequilibrium distributions. We study the effects of interactions on quantum relaxation towards equilibrium for a system of one-dimensional coupled harmonic oscillators. We show by numerical simulations that interactions can delay or even prevent complete relaxation for some initial states. We also discuss how this effect might be relevant for cosmological scenarios and how nonequilibrium could be detected in some models.

quant-ph↗

arXiv2019

On the Thermodynamical Black Hole Stability in the Space-time of a Global Monopole in $f(R)$-Gravity

In this work, we re-assess a class of black hole solutions in a global monopole spacetime in the framework of an $f(R)$-gravity model. Our main line of investigation consists in considering a region close enough to the black hole, but such that the weak field approximation is still valid. The stability of the black hole is studied in terms of its thermodynamical properties, with the radial coordinate written as a power law function with the status of the main factor underneath the stability of the model. We obtain the explicit expressions for the thermodynamical quantities of the black hole as functions of the event horizon, by considering both the Hawking and the local temperatures. The phase transitions that may occur in this system, including the Hawking-Page phase transition, are inspected with particular attention. We work out and contemplate a solution of special interest in which one of the parameters is related to the cosmological constant. Our main result sets out to establish a comparison between both the Hawking and the local formalisms for the black hole in the framework of the $f(R)$-gravity in the particular space-time adopted here.

hep-th↗