arXiv subjects

Fabiano F. Santos

Publications and source records attributed to Fabiano F. Santos.

27 records · Page 2Linked to original sources

arXiv2024

de Sitter versus anti-de Sitter in Horndeski-like gravity

We present general solutions of Horndeski-like gravity that can interpolate between the de Sitter and anti-de Sitter regimes. In particular, we develop the first-order formalism with two scalar fields, and considering a black hole ansatz with flat slicing we investigate three different cases, namely exponential, vacuum, and smooth superpotential solutions, with no Minkowski extrema. Furthermore, with these solutions we show that a Renormalization Group flow is established, and we obtain a turnaround in the warp factor, where the transition is bounded by the area low. We discuss the ideal regimes to trap gravity, which are constructed using the holographic function, which provides stable and unstable regimes to localize gravity. Finally, we show that no ghost appear and that the matter sector that violates the $c$-theorem is physical.

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arXiv2023

AdS/BCFT correspondence and Horndeski gravity in the presence of gauge fields: holographic paramagnetism/ferromagnetism phase transition

This paper presents a dual gravity model for a (2+1)-dimensional system with a limit on finite charge density and temperature, which will be used to study the properties of the holographic phase transition to paramagnetism-ferromagnetism in the presence of Horndeski gravity terms. In our model, the non-zero charge density is supported by a magnetic field. As a result, the radius $ρ/B$ indicates a localized condensate, as we increase the Horndeski gravity parameter, that is represented by $γ$. Furthermore, such condensate shows quantum Hall-type behavior. This radius is also inversely related to the total action coefficients of our model. It was observed that increasing the Horndeski parameter decreases the critical temperature of the holographic model and leads to the harder formation of the magnetic moment at the bottom of the black hole. However, when removing the magnetic field, the ferromagnetic material presents a disorder of its magnetic moments, which is observed through the entropy of the system. We also found that at low temperatures, spontaneous magnetization and ferromagnetic phase transition.

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arXiv2023

Exploring the shear viscosity in four-dimensional planar black holes beyond General Relativity

The well known shear viscosity to entropy density ratio ($η/s$) cannot be computed when the black hole space-time has zero thermodynamic entropy. This is the case, for example, when General Relativity in four dimensions is complemented with Critical Gravity, or in particular scenarios within the Four-dimensional-scalar-Gauss-Bonnet theories. Recently, it has been shown that the zero entropy situation can be overcome in these examples by introducing suitable matter fields. With this at hand, in this paper we analyze each case and the impact of these extra sources in the ratio, in terms of their new parameters. We find that, while the $η/s$ ratio remains constant and insensitive in the former, this is not the case for the latter. To perform the calculations, we construct a Noether charge using a space-like Killing vector. The accuracy of the aforementioned findings is supported by the Kubo formalism.

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arXiv2022

Holographic complexity of braneworld in Horndeski gravity

This work investigates the influence of a probe string on the complexity of braneworld according to the CA (Complexity equals action) conjecture within the Horndeski gravity. In the current study, it is considered that scalar fields that source Horndeski gravity has a spatial dependence. In addition, our system contains a particle moving on the boundary, which corresponds to the insertion of a fundamental string in the higher dimensional bulk. Such an effect is given by the Nambu-Goto term, which also incorporates the time-dependence and evolution in our system. Both warp factor, scalar field, and superpotential values are derived numerically assuming appropriate initial conditions, and the growth rate of holographic complexity is analyzed within the so-called Wheeler-De Witt (WDW) patch with null-like hypersurfaces present.

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arXiv2022

Studies of transport coefficients in charged AdS$_{4}$ black holes on $κ$-deformed space

In this work, we study the effect of $κ$-deformed space on the thermodynamic quantities, this are find through the holographic renormalization that provide the free energy, which is fundamental to derive the another thermodynamic quantities. For this scenario we consider an charged AdS$_{4}$ black hole for an Einstein-Maxwell model where the derivative quadrivector is replaced by a deformed version inspired in Kaniadakis statistics. Besides, we extract the transport coefficient know as electrical conductivity.

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arXiv2022

Shear viscosity from black holes in generalized scalar-tensor theories in arbitrary dimensions

In higher dimensions, we study Degenerate-Higher-Order-Scalar-Tensor theories and we derive solutions that resemble the Schwarzschild Anti-de Sitter black holes. We compute their thermodynamic quantities following the Wald formalism, satisfying the First Law of Thermodynamics and a higher dimensional Smarr relation. Constructing a Noether charge with a suitable choice of a space-like Killing vector, we obtain the shear viscosity of the non-gravitational dual field theory, where for a suitable choice of the couplings functions, the Kovtun-Son-Starinets bound is violated. These results are corroborated by the calculation of the Green's functions following the Kubo formalism.

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arXiv2022

AdS/BCFT correspondence and BTZ black hole within electric field

This paper, presents the gravity duals of Conformal Field Theories with boundaries. This theory is known as AdS/BCFT correspondence. In this duality, our system has 3D gravity coupling with the Maxwell field dual to 2D BCFT. On the gravity side, we consider a 3D BTZ black hole. We analyze the effects of the chemical potential on the profile of the extra boundary for the black hole. Performing a holographic renormalization, we calculate the free energy and obtain the total entropy and corresponding area with chemical potential, and the boundary entropy for the black hole. These theories are specified by stress-energy tensors that reside on the extensions of the boundary to the bulk. In this way, the AdS/BCFT appears analogous to the fluid/gravity correspondence with the chemical potential. We discuss the solutions as well as their thermodynamic and fluid properties.

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arXiv2022

AdS/BCFT correspondence and Lovelock theory in the presence of canonical scalar field

In the current study, authors present the comprehensive analysis of the Anti-de Sitter/Boundary Conformal Field Theory (AdS/BCFT) correspondence for Lovelock theory of second order in the presence of canonical (and real) scalar field non-minimally coupled to modified gravitation sector. Authors consider the special case with three dimensional BTZ (Banados-Teitelboim-Zanelli) black hole and dual 2D Conformal Field Theory with the additional boundary for higher dimensional AdS spacetime. Moreover, for the given case additional boundary profile was investigated, as well as the holographic renormalization procedure for Lovelock-scalar theory. Besides, from holographic renormalization black hole entropy was obtained numerically. Finally, from the entropy and black hole temperature dual to BCFT some thermodynamical quantities, such as heat capacity, sound speed, energy-momentum trace and Hawking-Page phase transition were probed.

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arXiv2021

AdS/BCFT correspondence and BTZ black hole thermodynamics within Horndeski gravity

In this work, we study gravity duals of conformal field theories with boundaries known as AdS/BCFT correspondence, put forward by Takayanagi [1], within a scalar-tensor theory, as proposed by Horndeski in 4D [2]. We consider the case of 3D gravity dual to 2D BCFT, take a Gibbons-Hawking surface term modified by Horndeski's theory and find the corresponding 3D (BTZ) black hole solutions. We analyze the effects of Horndeski's gravity on the profile of the extra boundary for the black hole by using an approximate analytic solution. Performing a holographic renormalization, we have calculated the free energy and obtained the total entropy and the corresponding area, as well as the boundary entropy for the black hole. In particular, the boundary entropy found here, can be seen as an extension of the one proposed by Takayanagi. From the free energy, we have done a systematic study of the 3D black hole thermodynamics and present, among our results, an indication of restoration of conformal symmetry for high temperatures. Finally, we present a study on the influence of the Horndeski's gravity on the Hawking-Page phase transition where we can see the stable and unstable phases throughout the plane of free energy {\sl versus} temperature.

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