arXiv subjects

Ernesto Contreras

Publications and source records attributed to Ernesto Contreras.

At least 19 recordsLinked to original sources

arXiv2026

Evading Cauchy horizon excision in scalarized regular black holes

Spontaneous scalarization provides a dynamical mechanism to evade the no-hair paradigm, but it has been argued to generically eliminate the Cauchy horizon in charged black holes. We show that this obstruction is not universal, but instead follows from the sign-definite structure of the Einstein-Maxwell source term. Within the $P$-dual formulation of nonlinear electrodynamics, we derive a general condition under which the effective scalar source changes sign between the horizons, allowing the integral constraint to be satisfied without destroying the Cauchy horizon. This establishes that the fate of the Cauchy horizon depends on the electromagnetic coupling and identifies candidate theories where scalarized horizons may persist. The resulting framework opens the possibility of studying scalarization in the interhorizon region and its interplay with mass inflation.

gr-qc↗

arXiv2026

Logarithmic corrections to black hole entropy from minimum-assumptions discretization

We introduce here a general model, under agnostic and minimum assumptions, to uniquely find the entropy area law with a corresponding fixed logarithmic correction term. In this approach, the horizon is discretized into generic Planck-scale cells representing coarse-grained indistinguishable geometric structures, and it is just the statistical combinatorial counting that determines the form of the entropy terms. We highlight the role of the assumptions and their comparison with known models providing fixed logarithmic contributions to the entropy.

gr-qc↗

arXiv2026

Horizon Microstructure Thermodynamics in AdS Black Holes: Smarr-Consistent Excitation Enthalpy

In this work we formulate a horizon-microstructure description of four-dimensional AdS black holes in which a horizon of area $A$ is resolved into $\mathcal{N}=A/a_p$ microscopic sites and $N$ occupied horizon sites. The central result is that the combinatorics of this partially occupied horizon sector yields the entropy directly: in the finite-filling regime the leading term is proportional to the area, and the maximal-entropy filling reproduces the Bekenstein--Hawking law with $a_p=4\ln 2\ \ell_{p}^{2}$. Subleading corrections include a subtractive logarithmic term and an inverse-area expansion. We then show that this partially occupied regime admits a thermodynamic justification from an extended first law with chemical potential $\mu$, a Smarr-consistent excitation enthalpy $\delta M(A,P,N)$, and an AdS control parameter $u=PS$. In this interpretation, the combinatorics provides the dominant horizon entropy, while the thermodynamic sector supplies a dressing that selects the equilibrium filling and assigns a finite excitation cost to departures from a reference partially occupied configuration.

hep-th↗

arXiv2025

Traversable ghost wormholes

Ghost stars are compact configurations characterized by an arbitrarily small total mass. Such objects require regions of negative energy density -a condition typically regarded as unphysical within the context of conventional stellar models. Nevertheless, negative energy densities arise naturally in traversable wormhole geometries, where the violation of the null energy condition is essential to sustain the flaring-out behavior at the throat. This connection suggests that ghost-like configurations may find a natural realization within wormhole physics. In this work, we investigate the existence of ghost configurations by analyzing their associated Hawking mass. Although in spherical symmetry the Misner and Hawking masses are known to coincide, we show that when the ghost condition is extended beyond spherical symmetry and applied to the Hawking mass, it faces topological obstructions that hinder its straightforward realization. As a concrete example, we demonstrate that a Casimir-like traversable wormhole can be naturally constructed within this framework. Finally, to illustrate the properties of the resulting geometry, we analyze its Penrose-Carter diagram.

gr-qc↗

arXiv2025

General Framework for the Spontaneous Scalarization of Regular Black Holes

We investigate the spontaneous scalarization of generic, static, and spherically symmetric regular black holes supported by nonlinear electrodynamics. Starting from an arbitrary seed metric, we employ the P-dual formalism to reconstruct the electromagnetic sector and subsequently couple a real scalar field nonminimally. As a worked example, we apply the framework to the regular Balart-Vagenas black hole, showing that scalarized and scalar-free branches can coexist in a region where the scalarized configurations are entropically preferred. We further assess possible observational imprints, finding percent-level deviations in both the shadow size and the fundamental scalar quasi-normal modes ($< 10\%$ for small charge-to-mass ratios), indicating that current electromagnetic and gravitational-wave observations do not rule out these solutions. Our construction thus provides a general route to explore scalarization on top of nonlinear-electrodynamics-supported spacetimes, extending beyond specific Reissner-Nordstr\"om-like cases.

gr-qc↗

arXiv2025

Hyperbolic Casimir-like wormhole

We present a systematic study of exact solutions for traversable wormhole geometries in a static and hyperbolic symmetric spacetime. In the conventional form of studying wormhole geometry, traversability requires the presence of exotic matter, which also provides negative gravity effects to keep the wormhole throat open. Using hyperbolic symmetry we obtain a solution already provided with negative energy density that replaces this effect and allows us to derive wormhole geometries that effectively violate the null energy condition. To achieve this goal, we use a generalized complexity factor for hyperbolic symmetry adapted to study wormhole geometries and with a suitable redshift function in order to construct a Casimir-like traversable hyperbolic wormhole. A detailed study has been conducted on the behavior of the matter sector, the energy conditions, and the traversability conditions.

gr-qc↗

arXiv2023

Quasi normal modes of a Casimir--like traversable wormhole through the semi-analytical WKB approach

In this work, we implement the semi-analytical WKB method to explore the behaviour of a scalar field on a traversable wormhole space--time with a Casimir--like complexity reported in Eur. Phys. J. C 82, 420 (2022). We estimate the error in the computation of the quasi--normal frequencies of the scalar field at each order in the WKB and show that the order with the best accuracy is not unique. We compute the value of the quasinormal frequencies for the smallest estimated error. As an aside, we find that the imaginary part of the quasinormal modes frequencies approach to zero for the fundamental mode mimicking the so--called quasi--resonance observed for massive scalar fields in the Reissner--Nordström background.

gr-qc↗

arXiv2023

Quasi Normal Modes of hairy black holes at higher--order WKB approach

In this work, we implement the $13^{th}$ order semi-analytical WKB method to explore the stability of hairy black holes obtained in the framework of Gravitational Decoupling. In particular, we perform a detailed analysis of the frequencies of the quasi-normal modes as a function of the primary hair of the solutions with the aim to bound their values. We explore a broad interval in a step of 0.1 of the hair parameters. We find that except for some cases where the method is expected to have poor accuracy, all the solutions seem to be stable and the role played by the primary hair is twofold: to modulate the damping factor of the perturbation and to decrease the frequency of its oscillation.

gr-qc↗

arXiv2023

GUP corrections to black hole thermodynamics in the extended phase space approach

In this work, we study corrections to black hole temperature and entropy in the context of the generalized uncertainty principle. In particular, we obtain corrected asymptotically anti de-Sitter black hole solutions following the extended phase space scheme in which the cosmological constant is considered as a thermodynamic pressure satisfying certain equation of state. Among all the possibilities, we consider that the cosmological pressure satisfies either a Polytropic or a Chaplygin equation of state. The physical plausibility of the solutions is studied based on the energy conditions and the associated heat capacity.

gr-qc↗

arXiv2022

$2+1$ Einstein-Klein-Gordon black holes by gravitational decoupling

In this work we study the 2+1 Einstein-Klein-Gordon system in the framework of Gravitational Decoupling. We associate the generic matter decoupling sector with a real scalar field so we can obtain a constraint which allows to close the system of differential equations. The constraint corresponds to a differential equation involving the decoupling functions and the metric of the seed sector and will be independent of the scalar field itself. We show that when the equation admits analytical solutions, the scalar field and the self-interacting potential can be obtained straightforwardly. We found that, in the cases under consideration, it is possible to express the potential as an explicit function of the scalar field only for certain particular cases corresponding to limiting values of the parameters involved.

gr-qc↗

arXiv2021

Thermodynamics of scale-dependent Friedmann equations

In this work, the role of a time-varying Newton constant under the scale-dependent approach is investigated in the thermodynamics of the Friedman equations. In particular, we show that the extended Friedman equations can be derived either from equilibrium thermodynamics when the non-matter energy momentum tensor is interpreted as a fluid or from non-equilibrium thermodynamics when an entropy production term, which depends on the time-varying Newton constant, is included. Finally, a comparison between black hole and cosmological thermodynamics in the framework of scale--dependent gravity is briefly discussed.

gr-qc↗

arXiv2021

Four dimensional Einstein-power-Maxwell black hole solutions in scale-dependent gravity

In the present work, we extend and generalize our previous work regarding the scale dependence applied to black holes in the presence of non-linear electrodynamics [1]. The starting point for this study is the Einstein-power-Maxwell theory with a vanishing cosmological constant in (3+1) dimensions, assuming a scale dependence of both the gravitational and the electromagnetic coupling. We further examine the corresponding thermodynamic properties and how these quantities experience deviations from their classical counterparts. We solve the effective Einstein's field equations using the "null energy condition" to obtain analytical solutions. The implications of quantum corrections are also briefly discussed. Finally, we analyze our solutions and compare them to related results in the literature.

gr-qc↗

arXiv2020

Regular decoupling sector and exterior solutions in the context of MGD

We implement the Gravitational Decoupling through the Minimal Geometric Deformation method and explore its effect on exterior solutions by imposing a regularity condition in the Tolman--Oppenheimer--Volkoff equation of the decoupling sector. We obtain that the decoupling function can be expressed formally in terms of an integral involving the $g_{tt}$ component of the metric of the seed solution. As a particular example, we implement the method by using the Schwarzschild exterior as a seed and we obtain that the asymptotic behavior of the extended geometry corresponds to a manifold with constant curvature.

gr-qc↗

arXiv2020

Extra packing of mass of anisotropic interiors induced by MGD

In this work we investigate the extra packing of mass within the framework of gravitational decoupling by means of Minimal Geometric Deformation approach. It is shown that, after a suitable set of the free parameters involved, the like--Tolman IV solution extended by Minimal Geometric Deformation not only acquire extra packing of mass but it corresponds to a stable configuration according to the adiabatic index criteria. Additionally, it is shown that the extra packing condition induce a lower bound on the compactness parameter of the seed isotropic solution and a stringent restriction on the decoupling parameter.

gr-qc↗

arXiv2020

Anisotropic 2+1 dimensional black holes by gravitational decoupling

In the present paper, we analyze the well-known 2+1 dimensional black holes (assuming a non-vanishing cosmological constant) in light of the gravitational decoupling by the minimal geometric deformation approach. To illustrate our results, we consider the BTZ geometry as the seed solution to generate new anisotropic ones. To complement the study, the curvature scalars and the energy conditions are analyzed.

gr-qc↗

arXiv2020

Gravitational Decoupling in Cosmology

Whereas the nature of dark components in the Universe remains unknown, alternative models of gravity have been developed to offer a geometric explanation to the origin of such components. In this work we use the Minimal Geometric Deformation approach to study extensions of the theory of General Relativity in a cosmological context. This is possible since such approach allows the decoupling of gravitational sources, and the Einstein field equations can be analytically solved with the presence of a new gravitational sector once a known GR solution is considered. In particular, we implement such approach in Friedmann-Robertson-Walker and Kantowski-Sachs universes. We demonstrate that the gravitational decoupling leads to modifications of well known cosmological solutions. For instance, we show that an effective spatial curvature in the Friedmann-Robertson-Walker metric, as well as several kind of matter components in the Kantowski-Sachs case, are obtained. Thus, we found that it is possible to obtain spatial curvature and new matter terms from geometry, which in cosmology they could be useful in addressing problems such as the spatial flatness of the Universe, dark matter and dark energy.

gr-qc↗

arXiv2020

Black hole shadow of a rotating scale--dependent black hole

In this work, starting from a spherically symmetric scale--dependent black hole, a rotating solution is obtained by following the Newman--Janis algorithm without complexification. Besides studying the horizon, the static conditions and causality issues of the rotating solution, we get and discuss the shape of its shadow.

gr-qc↗

arXiv2020

Beyond classical anisotropy and a new look to relativistic stars: a gravitational decoupling approach

In this article, we propose a physical condition to extend interior isotropic solutions to anisotropic domains by gravitational decoupling in the framework of the Minimal Geometric Deformation approach. In particular, it is found that by using an expression reminiscent of the classical anisotropy factor, we can close the decoupling system of equations and a new anisotropic solution can be found. As an example, we extend the well--known Tolman IV.

gr-qc↗