arXiv subjects

Jonathan A. Rebouças

Publications and source records attributed to Jonathan A. Rebouças.

12 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

Optical effects of one-sided Kiselev-type quintessence in reflection-asymmetric polymer thin-shell wormholes

Strong-field rays that traverse a wormhole can carry optical information about an exterior inaccessible to the observer. We investigate this mechanism in a reflection-asymmetric thin-shell wormhole formed by joining a pure-polymer exterior containing the observer and emitting disk to a polymer geometry with a Kiselev-type anisotropic environment on the opposite side. Equal masses and a common polymer scale, angular geometry, and throat position isolate the effect of one-sided quintessence. We derive the shell-frame optical matching and calculate matched critical scales, null-ray topologies, orbit numbers, transfer functions, and face-on intensity maps for three emission prescriptions. The matching projects the opposite-side photon barrier onto a distinct inner edge of the observer screen, while the outer cosmological-type horizon partitions cross-throat rays into returned and terminal families. Across the admissible parameter grid, increasing the environmental amplitude widens the returned screen interval, increasing the polymer correction contracts it, and changing the environmental exponent produces competing trends. Observer-side orbit numbers and ordinary transfer branches remain invariant under changes confined beyond the throat, providing an exact control, whereas returned branches move and broaden. Once these branches enter the emitting support, they generate additional inner annuli at source-dependent onset strengths. The combined geometric and radiative analysis identifies a controlled cross-throat optical response to one-sided quintessence and shows how environmental information beyond the throat is encoded in matched critical structure and image morphology.

gr-qc↗

arXiv2026

Thin-shell wormholes in cosmic voids

Cosmic voids are underdense regions that can provide an effective large-scale environment with a de Sitter-like gravitational behavior. Motivated by recent black-hole solutions embedded in void density profiles, we construct a symmetric thin-shell wormhole by gluing two copies of the positive-lapse region of a black hole inside a cosmic void. The surface stresses are obtained from the Darmois--Israel junction conditions, and the corresponding null, weak, dominant, and strong energy-condition combinations are written directly in terms of the void mass function and density profile. We further develop the thermodynamics of the static shell, deriving a first law that relates the shell entropy to the black-hole and cosmological-like horizon entropies. We then formulate the radial dynamics of the throat through an effective potential and study the local stability of static configurations when the exotic matter on the shell obeys either a generalized cosmic Chaplygin gas or a modified cosmic Chaplygin gas equation of state. In both models the Chaplygin parameter $B$ is fixed by the static junction condition, so that the remaining stability test is governed by the void geometry and by the equation-of-state parameters. Numerical results reveal that GCCG-supported configurations are generically unstable, whereas MCCG-supported wormholes can be stable for a sufficiently large linear term in the equation of state. The resulting framework connects the de Sitter-like structure of cosmic voids with the standard thin-shell wormhole formalism and provides a starting point for identifying stable or unstable wormhole configurations located between the black-hole and cosmological-like horizons of the void spacetime.

gr-qc↗

arXiv2026

Bayesian constraints on quadratic $f(Q)$ gravity from the ADM mass of white dwarfs

We calculate static equilibrium sequences for white dwarfs (WDs) in quadratic symmetric teleparallel gravity, f(Q)=Q+alpha Q^2, and perform a Bayesian comparison between the negative-coupling sector, general relativity (GR), and the positive-coupling sector using mass-radius measurements. Regular interior solutions are obtained by imposing the affine field equation and selecting the analytic branch C=r exp(B/2), and are matched to asymptotically flat exterior spacetimes to determine the ADM mass. The matter sector is described by a cold carbon-12 equation of state including relativistic electron degeneracy, nuclear rest energy, and Coulomb lattice corrections. Central density is marginalized at fixed alpha with a log-uniform prior. The sequences span 10^14 <= |alpha|/cm^2 <= 10^21. Positive couplings shift the compact branch toward larger radii and lower masses, whereas negative couplings produce high-mass extensions, including an admissible equilibrium configuration with M_ADM=14.34 solar masses. Using Sirius B, QS Vir, V471 Tau B, ZTF J1901+1458, and LHS 4033, we obtain conditional posterior medians alpha_-= -1.12x10^16 cm^2 and alpha_+=1.85x10^17 cm^2. With equal prior weights, the posterior probabilities for the negative, GR, and positive sectors are 0.228, 0.378, and 0.395, respectively, with ln(B_+/GR)=0.043. Current data therefore provide conditional constraints on the coupling but no direct evidence for modified gravity, emphasizing that the ADM mass prescription and admissible stellar domain must be consistently defined when using WD observations to constrain the theory.

gr-qc↗

arXiv2026

White Dwarf Stellar Structure from Effective Polymer Geometry in Loop Quantum Gravity

We construct an effective Tolman Oppenheimer Volkoff system for cold carbon white dwarfs using the areal radius form of a polymer metric sector motivated by loop quantum gravity. The two asymptotic mass parameters of the geometry are retained in the stellar prescription through $M_B\rightarrow m(R)$ and $M_W=ηm(R)$, while the polymer amplitude is controlled by $A_λ$. The matter sector is kept fixed and is described by the Chandrasekhar equation of state and by the same carbon model with the Coulomb lattice correction. The resulting equations recover the general relativistic TOV system and the symmetric polymer limit. For the undeformed sequences we obtain $M_{\max}=1.4166\,M_\odot$ for the Chandrasekhar model and $M_{\max}=1.3850\,M_\odot$ when the lattice correction is included. Turning on $A_λ$ shifts the massive part of the equilibrium sequence upward without stiffening the equation of state, reaching $M_{\max}=1.7125\,M_\odot$ and $1.6907\,M_\odot$ at $A_λ=100$ for the two matter models. These configurations remain within the matter domain imposed by the inverse beta decay boundary used in the scan. The asymmetric ratio $η=M_W/M_B$ changes the metric function near the polymer transition region, but its effect on white dwarf observables is small: across the selected configurations, $M_{\max}$ changes by less than $0.1\%$ and the corresponding radius by less than $0.33\%$. The calculation therefore identifies $A_λ$ as the parameter controlling the super Chandrasekhar displacement of the mass radius relation, while $η$ acts mainly as a geometric asymmetry parameter in the low compactness regime probed by white dwarfs.

astro-ph.SR↗

arXiv2026

Junction Conditions, Radial Stability, Thermodynamics, Optical Geometry and Appearance of Polymer-Quintessence Thin-Shell Wormholes

Thin-shell wormholes built from effective black hole geometries are sensitive not only to the lapse function but also to the choice of areal radius. We construct a reflection-symmetric thin-shell wormhole from the positive-lapse sector of a polymer black hole surrounded by Kiselev-type quintessence and keep the nonareal angular function throughout the junction, stability, thermodynamic, and optical analyses. The Israel junction conditions give a negative surface energy density for every static throat on the positive branch, while the tangential null and intrinsic strong energy combinations are controlled by the local lapse slope. The radial dynamics is written as an effective-potential problem in which the nonareal sector produces a momentum-flux term and modifies the local stability criterion for surface equations of state with explicit radius dependence. For the sampled calibrated configurations, the linear barotropic and variable phantomlike closures remain locally unstable, whereas the variable Chaplygin gas admits finite linear radial stability windows. The same geometric correction also modifies the local first-law balance and shell entropy bookkeeping, while the optical analysis shows that cross-throat propagation generates additional inner image branches despite the wormhole and black hole geometries sharing the same exterior critical curve. These results identify how polymer corrections and a quintessence environment jointly reorganize the matter content, radial response, thermodynamic bookkeeping, and optical appearance of the resulting thin-shell wormhole.

gr-qc↗

arXiv2026

Gravitational Lensing in a Kasner Background: Distinguishing Wormholes and Black Holes

We investigate gravitational lensing by compact objects embedded in anisotropic Bianchi-I cosmologies using directional Jacobi maps within the thin-lens approximation. The formalism is developed for a general diagonal Bianchi-I spacetime and specialized to the Kasner solution as an analytically tractable background. Using the Ellis--Bronnikov wormhole and the Schwarzschild black hole as representative lenses, we derive anisotropic lens equations, characteristic axis-aligned lensing scales, and the corresponding critical curves. We show that the directional splitting of the characteristic scales depends on the complete source--lens--observer optical propagation and provides a geometric probe of anisotropic expansion independent of the overall lens scale. By contrast, the exact critical curves exhibit a much weaker deformation, indicating that characteristic-scale splitting and critical-curve morphology probe distinct aspects of the lens mapping. The comparison between wormhole and black-hole lenses further reveals that identical anisotropic backgrounds are filtered differently by distinct weak-field deflection laws. These results provide a simple framework for disentangling cosmological anisotropy from the local geometry of compact lenses.

gr-qc↗

arXiv2026

Thin-Shell Wormholes from Entropy-Induced Black-Hole Geometries

Modified black-hole entropies can induce effective spacetime geometries and thereby provide a thermodynamic route for investigating thin-shell wormholes. In this work, we construct symmetric cut-and-paste wormholes from the generic entropic lapse function $F_{\mathcal S}(r)=1-4πM/\mathcal S'(r)$ and formulate the Darmois--Israel junction conditions directly in terms of the lapse and of the entropy derivatives. We derive the surface stresses, shell energy-condition combinations, conservation equation, and radial effective potential, and then apply the formalism to the Bekenstein--Hawking, Barrow, Tsallis--Cirto, Rényi, Kaniadakis, logarithmic, loop-quantum-gravity-inspired, and exponential entropy prescriptions. The analysis shows that the symmetric construction requires negative surface energy density throughout every admissible positive-lapse domain, although entropy deformations can significantly modify the horizon structure, the allowed throat region, and the localization of the surface stresses. Within the parameter domains considered here, all examined constant-barotropic branches are linearly radially unstable, despite quantitative changes in their near-horizon scales. In contrast, a variable Chaplygin shell can support stable configurations, with the stability domains determined jointly by the entropic geometry, the throat radius, and the radial exponent of the shell equation of state. These results establish a unified framework for comparing entropy-induced black-hole geometries as thin-shell wormhole seeds and show that stability is governed not by the entropy deformation alone, but by its interplay with the dynamical response of the matter localized at the throat.

gr-qc↗

arXiv2026

Distinguishing wormholes via Einstein rings and global curvature

In this work, we investigate the gravitational lensing properties of a static Ellis-Bronnikov wormhole embedded in a curved Friedmann-Lemaître-Robertson-Walker (FLRW) universe. By employing curvature-dependent cosmological distances, we derive the corresponding weak-field lens equation and demonstrate that the wormhole Einstein ring radius follows a characteristic cubic scaling with cosmological distances, in sharp contrast to the square-root behavior found for Schwarzschild black holes. This distinct scaling leads to a qualitatively different redshift evolution of the lensing signal, providing a model-independent geometric diagnostic to discriminate between wormhole and black hole lensing scenarios. Numerical analysis reveals that the interplay between the local wormhole geometry and the FLRW background produces an asymmetric response to spatial curvature that inverts at intermediate redshifts, exhibiting a non-negligible sensitivity even under tight modern constraints such as those from DESI 2024. We also find that Ellis-Bronnikov wormholes are substantially less efficient gravitational lenses than Schwarzschild black holes of comparable physical scale, implying that microarcsecond-scale Einstein rings require macroscopic throat radii. These results suggest that, should a population of cosmological wormholes exist, their lensing signatures could provide a sensitive, complementary probe of both exotic spacetime topology and the global geometry of the Universe.

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

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↗