arXiv subjects

Fabiano F. Santos

Publications and source records attributed to Fabiano F. Santos.

At least 19 recordsLinked to original sources

arXiv2026

Holographic Complexity as a Probe of Boundary Entropy in AdS/BCFT

We investigate how the sewing operations familiar from topological quantum field theory provide a useful organizational framework for semiclassical AdS/BCFT path integrals. Our purpose is not to identify AdS/BCFT with a topological field theory: the bulk geometry, the end-of-the-world brane, and the on-shell action remain intrinsically metric-dependent. Rather, we use the TQFT language of state preparation, orientation reversal, and gluing to separate interface data from local geometric contributions. For AdS$_3$/BCFT$_2$, we review how the Euclidean on-shell action and the Ryu--Takayanagi prescription reproduce the Affleck--Ludwig boundary entropy $\log g$ after holographic renormalization. We then formulate the Complexity=Action calculation in the presence of an end-of-the-world brane, carefully distinguishing bulk, brane, joint, and null-boundary contributions. We emphasize that finite terms in a relative Wheeler--DeWitt action depend on the choice of regulator matching and on the null-boundary counterterm scheme unless their scheme independence is established explicitly. Finally, we extend the geometric construction to a planar BTZ background and derive the brane embedding from the Neumann boundary condition. The resulting framework clarifies which aspects of holographic complexity are sensitive to boundary conditions and which require further renormalization input before they can be interpreted as universal boundary data.

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arXiv2026

Thermodynamics of Hairy Black Holes in Quantum Regimes: Insights from Horndeski Theory

We study non-perturbative quantum gravitational corrections to the thermodynamics and quantum work distribution of the $n$-dimensional Schwarzschild--Tangherlini--Anti-de Sitter black hole. Starting from the corrected entropy $S = S_0 + η\, e^{-S_0}$, where $S_0$ is the Bekenstein--Hawking entropy, we derive the modified specific heat, internal energy, Helmholtz free energy, and Gibbs free energy in closed form. The specific heat retains the classical divergence at $r_h^{*}=l\sqrt{(n-3)/(n-1)}$ for $n\geq 4$, but the quantum correction suppresses its magnitude by up to $78\%$ at small horizon radii. In the extended phase space, the uncharged black hole admits no van der Waals critical point; however, the non-perturbative correction induces a Hawking--Page transition for $n\geq 4$ that is absent in the semi-classical limit. The corrected Gibbs free energy turns negative at small $r_h$, opening a thermodynamic channel with no classical counterpart. Using the Jarzynski equality and Jensen inequality, we obtain the quantum work distribution during evaporation. The free energy difference $ΔF$ between two black hole states undergoes a sign reversal at small horizon radii for $n\geq 4$ when $η=1$, flipping the average quantum work from negative to positive. This sign reversal grows with the spacetime dimension, reaching $\langle W\rangle \approx +4.31$ for $n=10$. These findings demonstrate that non-perturbative quantum gravitational effects qualitatively alter the phase structure and evaporation energetics of AdS black holes, and they cannot be captured by perturbative corrections alone.

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arXiv2026

Building an AdS/BCFT Josephson junction within Horndeski gravity

This work explores the constriction and normal Josephson junctions of superconductors within Horndeski's gravitational theory framework. Through a single scalar field of this theory, we provide a dual holographic description via the AdS/BCFT correspondence. We identify a critical temperature below which a charged condensate forms through a second-order phase transition in constriction and normal junctions. Our findings reveal that the condensate comprises pairs of quasiparticles. The junctions between superconductors are characterized by weak links that lead to supercurrent flow, with their magnitude determined by the phase difference between the superconductors, which is modulated by the Horndeski parameters. The supercurrents are governed by the Josephson current-phase relation, highlighting the intricate interplay between gravitational theory and superconducting phenomena.

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arXiv2026

Black Hole Entropy and Complexity Growth in Horndeski Gravity within the AdS/BCFT Framework

This work investigates the connection between quantum complexity and gravitational dynamics within the framework of Horndeski gravity, extending the AdS/BCFT correspondence to include scalar-tensor interactions. By refining the "complexity=action" conjecture, we analyze how Horndeski gravity modifies the Wheeler-DeWitt patch and the causal structure relevant for holographic complexity. Our analysis shows that the linear growth of complexity, proportional to the product of black hole entropy and temperature, is recovered for the class of black hole configurations studied here, including rotating and charged solutions. We also study the effect of shock waves on complexity growth and find the appearance of the switchback effect. These conclusions hold in the regime in which the relevant effective characteristic cone of Horndeski gravity is compatible with the null structure used to define the Wheeler-DeWitt patch, so that the causal construction effectively matches that of the background metric. Within this domain of validity, our results provide evidence for the complexity=action conjecture in Horndeski gravity and illustrate how modified gravitational couplings affect holographic complexity in the AdS/BCFT framework.

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arXiv2026

A new rotating axionic AdS$_4$ black hole dressed with a scalar field

This paper presents a new four-dimensional axionically charged rotating black hole with a scalar field, which is defined by a structural function coupling the axionic field and a scalar potential. This configuration is characterized by an integration constant and two constant parameters. The thermodynamic quantities are obtained via the Euclidean procedure, where the validity of the first law of thermodynamics is ensured. These results indicate that the rotating configuration provides a useful framework for exploring holographic superconductors, where the angular constant parameter plays a central role.

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arXiv2025

A Cardy-like expression for charged rotating solitons and black holes

This paper aims to propose a Cardy-like formula characterized by the mass, charge, and angular components of the black hole, along with their corresponding solitonic configuration, obtained through a double Wick rotation. The expression also incorporates the dynamical exponent and effective spatial dimensionality as key elements. To validate the proposal, we first present a new concrete example in which recovering the semiclassical entropy requires the soliton to possess thermodynamic quantities beyond its mass. Additionally, we show more examples derived from static black hole solutions, employing a Lorentz boost to calculate their thermodynamic parameters. Finally, we include a case of a rotating configuration where the Lorentz boost is not required.

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arXiv2025

Probing the Black Hole Interior with Holographic Entanglement Entropy and the Role of AdS/BCFT Correspondence

This work explores the black hole information loss paradox, a fundamental challenge in theoretical physics. It proposes insights using Holographic Entanglement Entropy (HEE) and the AdS/BCFT correspondence within Horndeski gravity. The work revisits the time-dependent behavior of HEE to probe black hole interiors and examines its implications for the Page curve, which describes the entropy evolution of Hawking radiation. It also discusses the relationship between conformal field theory (CFT) microstates and black hole thermodynamics through the AdS/BCFT correspondence, suggesting that only a subset of microstates corresponds to black holes with smooth interiors, while others may involve firewalls. The study extends black hole thermal entropy to time-dependent entanglement entropy, offering a perspective on the interplay between quantum mechanics, thermodynamics, and gravity.

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arXiv2025

Holographic complexity and residual entropy of a rotating BTZ black hole within Horndeski gravity

This work explores the holographic complexity and residual entropy of a rotating BTZ black hole within the framework of Horndeski gravity. The investigation is motivated by the need to understand the emission of information from black holes, as encoded by quantum complexity, which persists even at zero temperature. Traditionally, black holes are considered to cease emitting information upon reaching zero temperature, yet our findings suggest a minimum level of information or minimal entropy. This challenges the classical notion of black hole death. Recent studies in the context of Horndeski gravity and the AdS/BCFT correspondence have identified a non-zero minimal entropy at zero temperature. Our work shows that complexity and entropy provide crucial insights into the information emission from black holes, extending beyond their classical death. These findings significantly affect our understanding of black hole thermodynamics and quantum information theory.

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arXiv2025

$κ$-Entanglement Entropy from Black Hole

In this work, we explore the entanglement entropy equipped with the $κ$-algebra. This entanglement entropy is computed through the geometric setup as performed by Hartman-Maldacena, which, in their prescription, finds that the entropy grows linearly in time. In our case, we show that the $κ$-algebra embedding provides a richer scenario where the third-order corrections in time added from $κ$-algebra to entanglement entropy imply that the growth of quantum correlations between subsystems is more intricate than a simple linear increase into the dynamics of black hole thermalization and quantum information flow. In the context of holography, such corrections suggest that the thermalization process is not instantaneous but involves higher-order interactions between subsystems.

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arXiv2025

Propagation of tensor perturbation in Horndeski-like gravity

Scalar-tensor theories have shown promise in many sectors of cosmology. However, recent constraints from the speed of gravitational waves have put severe limits on the breadth of models such classes of theories can realize. In this work, we explore the possibility of a Horndeski Lagrangian that is equipped with two dilaton fields. The evolution of a two-dilation coupled cosmology is not well-known in the literature. We explore the tensor perturbations in order to assess the behavior of the model again the speed of gravitational wave constraint. Our main result is that this model exhibits of a class of cosmological theories that is consistent with this observational constraint.

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arXiv2025

Cosmological scalar perturbations in Horndeski-like gravity

Scalar-tensor theories are promising dark energy models. A promising scalar-tensor theory, called Horndeski-like gravity, is coming from the application of the Horndeski gravity in string theory and cosmology that takes into account two dilaton fields. In this work we study the stability of the scalar sector of this theory and compare it with that coming from the previously studied tensor sector. With the first-order formalism we investigate the allowed background solutions. Focusing on the background solution with a single scalar field, the entropy coming from particle production $S_{in}$ and that of the apparent horizon $S$ will be studied, which translates into \textit{entropy bounds}. These entropy bounds are compared with the stability of the scalar and tensor sector as well. The gravitational slip (minus one) to entropy ratio is also considered as a possible replacement for the usual shear viscosity to entropy ratio for black holes.

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arXiv2025

Geometric Josephson junction

In this work, we present a gravitational dual to a constriction Josephson junction constructed from the AdS/BCFT correspondence. On the gravity side, we consider a planar AdS-Schwarzschild black hole. Our junction is connected by the boundary $\partialΩ$ with tension $Σ$ on the boundary CFT. This approach lead us to analytical solutions rather than usual numerical methods. Our computations on the gravity side reproduce the standard relation between the current across the junction and the phase difference of the condensate controlled by the tension $Σ$. We also study the maximum current's dependence on the junction's tension and size and reproduce familiar results.

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arXiv2024

Holographic Boundary Conformal Field Theory within Horndeski Gravity

We investigate entanglement islands and the Page curve in the framework of Horndeski gravity on a Karch-Randall braneworld background. In particular, treating the holographic boundary conformal field theory analytically we find that the Horndeski parameters significantly alter the behavior of the Page curve compared to standard general relativity, a feature caused by the nontrivial geometry induced by the Horndeski scalar field. Interestingly enough, the geometry far from the AdS limit plays a more significant role compared to previous studies. This suggests that Horndeski gravity introduces important modifications to the distribution of quantum information in the holographic model. Finally, we claim that holographic consistency can be used reversely to impose constraints on Horndeski gravity itself, providing a new tool for probing the validity of modified gravity theories.

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arXiv2024

q-Deformed glueballs spectrum in AdS/QCD correspondence

This work presents the application of the q-algebra in the glueballs spectrum. This algebra is implemented through Jackson derivatives in a Schrödinger-like equation resulting from the gravity fluctuations around the braneworld scenario in five dimensions. In our prescription, we consider a four-dimensional AdS$4$ brane, living in AdS$5$ bulk, that is also known for describing locally localized gravity via quasi-zero mode. At the appropriate limit, this background leads to confinement and allows us to find the shape of the $q$-deformed glueball spectrum in the AdS$5$/QCD$4$ correspondence. The introduction of the $q$-deformation provides us with a richer glueball spectrum.

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arXiv2024

From Einstein to Horndeski: Holographic Transport Coefficients in Modified Gravity

This paper examines the holographic computation of bulk and shear viscosity ratios in strongly coupled thermal plasmas using the AdS/BCFT correspondence within Horndeski gravity. We demonstrate that this framework leads to non-zero viscosity-to-entropy ratios ($ζ/S$ and $η/S$) at low temperatures, indicating a break in conformal symmetry. At high temperatures, these ratios approach zero, recovering the expected conformal behavior of quark-gluon plasma. Our findings provide new insights into the hydrodynamic properties of strongly coupled plasmas and offer a more nuanced understanding of QCD-like theories in holographic models.

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arXiv2024

Magnetized AdS/BCFT Correspondence in Horndeski Gravity

This work examines the thermodynamics and hydrodynamics behaviors of a five-dimensional black hole under the influence of an external magnetic field. The solution is the gravity dual to the Anti-de Sitter/Boundary Conformal Field Theory correspondence, enabling the study of properties within an anisotropic fluid framework. Utilizing holographic renormalization, we compute the free energy and the holographic stress tensor residing on the boundary denoted as $Q$. Within the fluid/gravity correspondence framework, we have a class of boundary extensions in $Q$, where the stress-energy tensor describes a magnetizing conformal fluid. We discuss the characteristics of this special solution as well as its thermodynamic properties, including the bulk and shear viscosity, the square of the speed of sound, as well as the anisotropic effects induced by the magnetic field in the magnetized conformal plasma.

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arXiv2024

Black branes in asymptotically Lifshitz spacetimes in $κ$-deformed Horndeski gravity

In this work we consider Horndesky gravity deformed by a parameter in its kinetic terms embedded in asymptotically Lifshitz spacetimes. We obtain black brane solutions in this geometry and study their thermodynamical properties. We show that the $κ$-deformation on the Horndeski kinetic terms allow for arbitrary values of the critical exponents characteristic of Lifshitz spacetimes. These solutions present local and global thermodynamical stabilites.

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arXiv2024

Thick branes in Horndeski gravity

We investigate thick brane solutions in the Horndeski gravity. In this setup, we found analytical solutions, applying the first-order formalism to two scalar fields where the first field comes from the non-minimal scalar-tensor coupling and the second is due to the matter contribution sector. With these analytical solutions, we evaluate the symmetric thick brane solutions in Horndeski gravity with four-dimensional geometry. In such a setup, we evaluate the gravity fluctuations to find ``almost massless modes'', for any values of the Horndeski parameters. These modes were used to compute the corrections to the Newtonian potential and evaluate the limit four-dimensional gravity.

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