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Milko Estrada

Publications and source records attributed to Milko Estrada.

At least 37 records · Page 2Linked to original sources
arXiv2023

A new class of regular Black Holes in Einstein Gauss Bonnet gravity with localized sources of matter

We provide a new regular black hole solution (RBH) in Einstein Gauss-Bonnet (EGB) gravity with localized sources of matter in the energy--momentum tensor. We determine the necessary constraints in order for the solution to be regular. Although we use a specific form for the energy density as a test of proof, these constraints could serve as a recipe for constructing several new RBH solutions in EGB gravity with localized sources. Due to that the usual first law of thermodynamics is not valid for RBH, so we rewrite the first law for EGB, which leads to correct values of entropy and volume. The size of the extremal black hole, whose temperature vanishes, becomes smaller for larger dimensions, whose radius could be of the order of the Planck units, thus the evaporation would stop once the horizon radius contracts up to a value close to the Planck length, which could be related with the apparition of quantum effects. Furthermore, the presence of matter fields in the energy--momentum tensor induces two phase transitions, where there are two regions of stability. This differs from the vacuum EGB solution, where the specific heat is always negative without phase transition as occurs in Schwarzschild black hole.

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arXiv2023

New regular 2+1 black hole solutions from bilocal gravity

We obtain new regular black hole solutions for an action in 2+1 dimensions with bilocal Ricci scalar and negative cosmological constant. Besides their connection to the cosmological constant, these solutions depend on a fundamental length due to their non-local nature. The effective profile densities that result from the non-local geometries have quasi-localized mass/energy since they are finite at the origin and their integration in all space is convergent. The black holes obtained are free of singularities and present one, two, or none horizons depending on the values of the involved parameters. The new solutions can have either an AdS, dS, or even a flat core. In the case of a de-Sitter core, it could represent a repulsive force coming from quantum effects. Although the resulting (effective) cosmological constant is positive near the origin, the classical (naked) counterpart is still negative thus precluding a cosmological horizon. We investigate the energy conditions of the effective source and determine the region where exotic energy should be found. Thermodynamic quantities are also computed. On the one hand, Gibbs's potential shows that both solutions are globally unstable, as in the BTZ case. On the other, we show that for small values of the horizon radius the Hawking temperature is negatively divergent but a finite size remnant can be defined where $T_H$ crosses zero. At this point, the heat capacity sign changes from negative to positive, indicating that the black holes are locally stable while irradiating. Thus, such a quantity, along with $T_H$, presents crucial differences with the BTZ black hole for small horizon radii where quantum effects become relevant. Finally, we analyze the bilocal black hole geodesics and find stable circular orbits for massless and massive particles, another feature absent in the BTZ case.

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arXiv2023

Dymnikova-Schwinger traversable wormholes

In this paper, we obtain new $d$-dimensional and asymptotically flat wormhole solutions by assuming a specific form of the energy density distribution. This is addressed by considering the generalization of the so-called Dymnikova model, originally studied in the context of regular black holes. In this way, we find constraints for the involved parameters, namely, the throat radius, the scale associated to the matter distribution, and the spacetime dimension, to build those wormholes. Following, we study the properties of the obtained solutions, namely, embedding diagrams as well as Weak and Null Energy Conditions (WEC and NEC). We show that the larger the dimension, the larger the flatness of the wormhole and the more pronounced the violation of these energy conditions. We also show that the corresponding fluid behaves as phantom-like for $d \geq 4$ in the neighborhood of the wormhole throat. In addition, we specialize the employed model for $d=4$ spacetime, associating it with the gravitational analog of the Schwinger effect in a vacuum and correcting the model by introducing a minimal length via Generalized Uncertainty Principle (GUP). Thus, we obtain a novel traversable and asymptotically flat wormhole solution by considering that the minimal length is very tiny. The associated embedding diagram shows us that the presence of this fundamental quantity increases the slope of the wormhole towards its throat compared with the case without it. That correction also attenuates the WEC (and NEC) violations nearby the throat, with the fluid ceasing to be a phantom-type at the Planck scale, unlike the case without the minimal length.

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arXiv2022

A new class of regular black hole solutions with quasi-localized sources of matter in $(2 + 1)$ dimensions

This paper investigates a new class of regular black hole solutions in (2 + 1)-dimensions by introducing a generalization of the quasi-localized matter model proposed by Estrada and Tello-Ortiz. Initially, we try to physically interpret the matter source encoded in the energy-momentum tensor as originating from nonlinear electrodynamics. We show, however, that the required conditions for the quasi-locality of the energy density are incompatible with the expected behavior of nonlinear electrodynamics, which must tend to Maxwell's theory on the asymptotic limit. Despite this, we propose a generalization for the quasi-localized energy density that encompasses the existing models in the literature and allows us to obtain a class of regular black hole solutions exhibiting remarkable features on the event horizons and their thermodynamic properties. Furthermore, since the usual version of the first law of thermodynamics, due to the presence of the matter fields, leads to incorrect values of entropy and thermodynamics volume for regular black holes, we propose a new version of the first law for regular black holes.

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arXiv2022

Representation of compact stars using the black string set--up

This work is devoted to provide a way of representing $4D$ spherically symmetric and static compact stellar configurations into a $5D$ space time, using the black string framework. We write the four and five dimensional line elements and the four and five dimensional energy momentum tensor such that the four and five dimensional quantities are related by a function $A(z)$, where $z$ represents to the extra dimension. Remarkably, one consequence of our chosen form for the line element, for the energy momentum tensor and for $A(z)$, is the fact that the $5D$ equations are reduced to the usual form of the four dimensional equations of motion. Also, the five dimensional conservation equation adopts the form of the four dimensional conservation equation. It is worth mentioning that, although our methodology is simple, this form of reduction could serve to represent other types of four dimensional objects into an extra dimension in future works. Furthermore, under our assumptions the sign of the pressure along the extra dimension is given by the trace of the four dimensional energy momentum tensor. Furthermore, our simple election for the function $A(z)$ modifies some features of the induced 4--dimensional compact stellar configuration, such as the mass--radius relation, the momentum of inertia, the central values of the thermodynamic variables, to name a few. Besides, the topology of this model is ${S}^{2}\times {S}^{1}$ and not the ${S}^{3}$ topology of the 5--dimensional structures.

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arXiv2022

A toy model for representing regular black holes at the black string style

We provide a way of representing a four dimensional regular black hole geometry at the black string style. We enunciate a list of constrains in order to that the complete five dimensional geometry to be regular. Following these constraints were constructed both the four and the five dimensional geometries. The assumptions used to solve the equations of motion suggest a relation between the $4D$ and the $5D$ Newton constants, which coincides with relations previously showed in the literature. Furthermore, the $(μ,ν)$ components of the five dimensional equations of motion adopt the form of the four dimensional equations of motion. Also, the five dimensional conservation equation adopts the form of the four dimensional conservation equation. At the origin the topology of the five dimensional geometry corresponds to the product between the four dimensional de--Sitter space--time and $S^1$ with $z$ compact. This latter differs from the Kaluza-Klein black string, where, at the origin the topology corresponds to the product between the Schwarzschild singularity and $R(S^1)$ for $z$ non compact (compact). The topology of the complete five dimensional geometry corresponds to $S^2 \times S^1$. At the infinity of the radial coordinate the topology corresponds to the product between Minkowski and $S^1$. At the induced four dimensional geometry we compute the first law of thermodynamics with the correct values of temperature and entropy.

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arXiv2022

An alternative study about the geometry and the first law of thermodynamics for AdS Lovelock gravity, using the definition of conserved charges

In this work it is introduced an extension of the study of the first law of thermodynamics of black holes based on the geometry of the extended phase space for AdS Lovelock gravities which includes changes of scales. As expected, the result obtained coincides with the previously known four dimensional case. For higher dimensions, the result is the arise of two new contributions to the first law of thermodynamics. The first term corresponds to corrections of the usual definition of thermodynamics volume at the horizon, due to the presence of the higher curvature terms. The second term arises in odd dimensions, comes from the asymptotic region, and corresponds to a scale transformation of the form $\propto \hatδ \ln (l/\ell)$, with $l$ the AdS radius and $\ell$ a parameter. A particularly interesting case corresponds to the Chern Simons gravity where the change scale does not generate a contribution at the asymptotic region, likely due to the Chern Simons AdS local symmetry.

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arXiv2022

Gravitational Decoupling algorithm modifies the value of the conserved charges and thermodynamics properties in Lovelock Unique Vacuum theory

We provide an extension of the Gravitational Decoupling (algorithm) for the Lovelock theory with Unique Vacuum (LUV), which represents a simple way to solve the equations of motion. Due to the application of this algorithm, the energy of the system splits in the {\it energy of the seed solution} and the {\it energy of each quasi-LUV sector}. Under certain assumptions imposed, the total energy varies due to the contribution of energy of each quasi-LUV sector. It is provided a new solution, whose energy differs from the energy of the seed solution in a quantity that depends on the number of extra sources. The new solution has two inner horizons, which is a proper characteristic of itself. Furthermore, its thermodynamics differs from the seed solution, since our solution is always stable and does not have phase transitions. Since the first law of thermodynamics is modified by the presence of the matter fields, we provide a new version of the first law for LUV, where a local definition of the variation of energy is defined, and, where the entropy and temperature are consistent for LUV theory.

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arXiv2021

A new model of regular black hole in $(2+1)$ dimensions

We provide a new regular black hole solution in $(2+1)$ dimensions with presence of matter fields in the energy momentum tensor, having its core a flat or (A)dS structure. Since the first law of thermodynamics for regular black holes is modified by the presence of the matter fields, we provide a new version of the first law, where a local definition of the variation of energy is defined, and, where the entropy and temperature are consistent with the previously known in literature. It is shown that the signs of the variations of the local definition of energy and of the total energy coincide. Furthermore, at infinite, the usual first law $dM=TdS$ is recovered. It is showed that the formalism used is effective to compute the total energy of regular black holes in $(2+1)$ with presence of matter in the energy momentum tensor. This latter suggests the potential applicability of this formalism to calculate the mass of other models of regular black holes in $d \ge 4$ dimensions.

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arXiv2021

A new exact solution of black-strings-like with a dS core

We provide a new five dimensional black string--like solution by means of the embedding of a four dimensional regular black hole into a compact extra dimension. We enunciate a list of constraints in order to that the five dimensional black string--like solution to be regular, and, following these constraints we construct our solution. Instead of the usual singularity, it is formed a core whose topology corresponds to the product between the de--Sitter core of the four dimensional Hayward solution and $S^1$. The horizon has topology $S^2 \times S^1$. At infinity of the radial coordinate the regular four dimensional geometry is asymptotically flat, {\it i.e}, at this place the topology of the complete solution corresponds to the product between Minkowski and $S^1$. At the induced four dimensional geometry we compute the correct values of temperature and entropy.

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arXiv2020

A note of the first law of thermodynamics by gravitational decoupling

We provide a way of decoupling the first law of thermodynamics in two sectors : the standard first law of thermodynamics and the quasi first law of thermodynamics. It is showed that both sectors share the same thermodynamics volume and the same entropy. However, the total thermodynamics pressure, the total temperature and the total local energy correspond to a simple sum of the thermodynamics contributions of each sector. Furthermore, it is showed a simple example, where there is a phase transition due to the behavior of the temperature at the quasi sector.

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arXiv2019

Thermodynamic extended phase space and $P-V$ criticality of black holes at Pure Lovelock gravity

In this work the \textit{chemistry} of asymptotically AdS black hole, charged and uncharged, solutions of Pure Lovelock gravity is discussed. For this the mass parameter of black holes is identified with the enthalpy of the system together with the promotion of the cosmological constant to a thermodynamics variable proportional to the \textit{pressure} of the system. The equations of state for both, charged and uncharged, are obtained. It is shown that the charged case behaves as a Van der Waals fluid. The existence of a first order phase transition between small stable/large stable black hole, which is a reminiscent of the liquid/gas transition, is found. The critical exponents of the thermal evolution, for different cases of interest, are similar to those of the Van der Waals fluid.

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arXiv2019

A way of decoupling gravitational sources in pure Lovelock gravity

We provide an algorithm that shows how to decouple gravitational sources in Pure Lovelock gravity. This method allows to obtain several new and known analytic solutions of physical interest in scenarios with extra dimensions and with presence of higher curvature terms. Furthermore, using our method, it is shown that applying the minimal geometric deformation to the Anti de Sitter space time it is possible to obtain regular black hole solutions.

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arXiv2019

Regular black holes with $Λ>0$ and its evolution in Lovelock gravity

In this work it is shown that the thermodynamics of regular black holes with a cosmological horizon, which are solutions of Lovelock gravity, determines that they must evolve either into a state where the black hole and cosmological horizons have reached thermal equilibrium or into an extreme black hole geometry where the black hole and cosmological horizons have merged. This differs from the behavior of Schwarzschild de Sitter geometry which evolves into a de Sitter space, the ground state of the space of solutions. This occurs due to a phase transition of the heat capacity of the black hole horizon. To perform that analysis it is shown that at each horizon a local first law of thermodynamics can be obtained from the gravitational equations.

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arXiv2019

Regular black holes and its thermodynamics in Lovelock gravity

In this work two new families of non-singular or regular black hole solutions are displayed. These black holes behave as de Sitter space near its center and have a well defined AdS asymptotic region for negative cosmological constant. These solutions are constructed on a general ground through the introduction of a finite density of mass/energy. This removes the usual singularity of a black hole and also introduces a new internal geometry. The thermodynamic properties of these solutions are discussed as well.

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arXiv2018

A new family of analytical anisotropic solutions by gravitational decoupling

This work is focused in the study of analytic anisotropic solutions to Einstein's field equations, describing spherically symmetric and static configurations by way of the gravitational decoupling through the method of Minimal Geometric Deformation (MGD). For this we apply MGD to Heintzmann's solution obtaining two new analytic and well behaved anisotropic solutions, in which all their parameters such as the effective density, the effective radial and tangential pressure, as well as radial and tangential sound speed, fulfill each of the requirements for the physical acceptability available in the literature.

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arXiv2016

Black hole at Lovelock gravity with anisotropic fluid

In this work a new family of black hole solutions in Lovelock gravity is discussed. These solutions describe anisotropic fluids which extend to the spatial infinity. Though far from the horizon their geometries approach some previously known black holes solutions the location of the horizons differ. Furthemore, although the masses of these solutions match the masses of those previously known black holes, their temperatures and entropies differ.

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