arXiv subjects

Ernesto Contreras

Publications and source records attributed to Ernesto Contreras.

At least 37 records · Page 2Linked to original sources

arXiv2020

Regularity condition on the anisotropy induced by gravitational decoupling in the framework of MGD

We use gravitational decoupling to establish a connection between the minimal geometric deformation approach and the standard method for obtaining anisotropic fluid solutions. Motivated by the relations that appear in the framework of minimal geometric deformation, we give an anisotropy factor that allows us to solve the quasi--Einstein equations associated to the decoupler sector. We illustrate this by building an anisotropic extension of the well known Tolman IV solution, providing in this way an exact and physically acceptable solution that represents the behavior of compact objects. We show that, in this way, it is not necessary to use the usual mimic constraint conditions. Our solution is free from physical and geometrical singularities, as expected. We have presented the main physical characteristics of our solution both analytically and graphically and verified the viability of the solution obtained by studying the usual criteria of physical acceptability.

gr-qc↗

arXiv2019

Radiative non-isothermal Bondi accretion onto a massive black hole

In this paper, we present the classical Bondi accretion theory for the case of non-isothermal accretion processes onto a supermassive black hole (SMBH), including the effects of X-ray heating and the radiation force due to electron scattering and spectral lines. The radiation field is calculated by considering an optically thick, geometrically thin, standard accretion disk as the emitter of UV photons and a spherical central object as a source of X-ray emission. In the present analysis, the UV emission from the accretion disk is assumed to have an angular dependence, while the X-ray/central object radiation is assumed to be isotropic. This allows us to build streamlines in any angular direction we need to. The influence of both types of radiation is evaluated for different flux fractions of the X-ray and UV emissions with and without the effects of spectral line driving. We find that the radiation emitted near the SMBH interacts with the infalling matter and modifies the accretion dynamics. In the presence of line driving, a transition resembles from pure type 1 & 2 to type 5 solutions (see Fig2.1 of Frank etal. 2002), which takes place regardless of whether or not the UV emission dominates over the X-ray emission. We compute the radiative factors at which this transition occurs, and discard type 5 solution from all our models. Estimated values of the accretion radius and accretion rate in terms of the classical Bondi values are also given. The results are useful for the construction of proper initial conditions for time-dependent hydrodynamical simulations of accretion flows onto SMBH at the centre of galaxies.

astro-ph.HE↗

arXiv2019

Minimal Geometric Deformation in a Reissner-Nordström background

This article is devoted to the study of new exact analytical solutions in the background of Reissner-Nordström space-time by using gravitational decoupling via minimal geometric deformation approach. To do so, we impose the most general equation of state, relating the components of the $θ$-sector in order to obtain the new material contributions and the decoupler function $f(r)$. Besides, we obtain the bounds on the free parameters of the extended solution to avoid new singularities. Furthermore, we show the finitude of all thermodynamic parameters of the solution such as the effective density $\tildeρ$, radial $\tilde{p}_{r}$ and tangential $\tilde{p}_{t}$ pressure for different values of parameter $α$ and the total electric charge $Q$. Finally, the behavior of some scalar invariants, namely the Ricci $R$ and Kretshmann $R_{μνωε}R^{μνωε}$ scalars are analyzed. It is also remarkable that, after an appropriate limit, the deformed Schwarzschild black hole solution always can be recovered.

gr-qc↗

arXiv2019

Anisotropic neutron stars by gravitational decoupling

In this work we obtain an anisotropic neutron star solution by gravitational decoupling starting from a perfect fluid configuration which has been used to model the compact object PSR J0348+0432. Additionally, we consider the same solution to model the Binary Pulsar SAX J1808.4-3658 and X-ray Binaries Her X-1 and Cen X-3 ones. We study the acceptability conditions and obtain that the MGD--deformed solution obey the same physical requirements as its isotropic counterpart. Finally, we conclude that the most stable solutions, according to the adiabatic index and gravitational cracking criterion, are those with the smallest compactness parameters, namely SAX J1808.4-3658 and Her X-1.

gr-qc↗

arXiv2019

Scale-dependent planar Anti-de Sitter black hole

In this work, we investigate four-dimensional planar black hole solutions in anti-de Sitter spacetimes in light of the so-called scale-dependent scenario. To obtain this new family of solutions, the classical couplings of the theory, i.e., the gravitational coupling and the cosmological constant, are not taken to be fixed values anymore. Thus, those classical parameters evolve to functions which change along the "height" coordinate, z. The effective Einstein field equations are solved, and the results are analyzed and compared with the classical counterpart. Finally, some thermodynamic properties of the presented scale--dependent black hole are investigated.

gr-qc↗

arXiv2019

Gravitational decoupling in $2+1$ dimensional space--times with cosmological term

In this work we implement the Minimal Geometric Deformation method to obtain the isotropic sector and the decoupler matter content of any anisotropic solution of the Einstein field equations with cosmological constant in $2+1$ dimensional space--times. We obtain that the solutions of both sectors can be expressed analytically in terms of the metric functions of the original anisotropic solutions instead of formal integral as in its $3+1$ counterpart. As a particular example we study a regular black hole solution and we show that, depending on the sign of the cosmological constant, the solutions correspond to regular black holes violating the null energy condition or to a non--regular black hole without exotic hair. The exotic/non--exotic and the regular/non--regular black hole dualities are discussed.

gr-qc↗

arXiv2018

Minimal Geometric Deformation in asymptotically (A-)dS space-times and the isotropic sector for a polytropic black hole

In the context of the Minimal Geometric Deformation method, in this paper we implement the inverse problem in a black hole scenario. In order to deal with an anisotropic polytropic black hole solution of the Einstein field equations with cosmological constant, the deformation method is slightly extended. After obtaining the isotropic sector and the decoupler for an anisotropic (A-)dS polytropic black hole solution, we emphasize a possible relation between anisotropization/isotropization and the violation of the energy conditions.

gr-qc↗

arXiv2018

Relativistic dust accretion onto a scale--dependent polytropic black hole

In this work we study steady and spherical relativistic dust accretion onto a static and spherically symmetric scale--dependent black hole. In particular we consider a polytropic scale--dependent black hole as a central object and obtain that the radial velocity profile and the energy density are affected when scale--dependence of the central object is taken into account and such a deviation is controlled by the so called running parameters of the scale--dependence models.

gr-qc↗

arXiv2018

Minimal Geometric Deformation: the inverse problem

In this paper we show that any static and spherically symmetric anisotropic solution of the Einstein field equations can be thought as a system sourced by certain deformed isotropic system in the context of Minimal Geometric Deformation-decoupling approach. To be more precise, we developed a mechanism to obtain an isotropic solution from any anisotropic solution of the Einstein field equations. As an example, we implement the method to obtain the sources of a simple static anisotropic and spherically symmetric traversable wormhole.

gr-qc↗

arXiv2018

Scale-dependent (2+1) - dimensional electrically charged black holes in Einstein-power-Maxwell theory

In this work we extend and generalize our previous work on the scale dependence at the level of the effective action of black holes in the presence of non-linear electrodynamics. In particular, we consider the Einstein-power-Maxwell theory without a cosmological constant in (2+1) dimensions, assuming a scale dependence of both the gravitational and the electromagnetic coupling and we investigate in detail how the scale--dependent scenario affects the horizon and thermodynamic properties of the classical black holes for any value of the power parameter. In addition, we solve the corresponding effective field equations imposing the "null energy condition" in order to obtain analytical solutions. The implications of quantum corrections are also briefly discussed.

hep-th↗

arXiv2018

Minimal geometric deformation decoupling in $2+1$ dimensional space-times

We study the minimal geometric deformation decoupling in $2+1$ dimensional space--times and implement it as a tool for obtaining anisotropic solutions from isotropic geometries. Interestingly, both the isotropic and the anisotropic sector fulfill Einstein field equations in contrast to the cases studied in $3+1$ dimensions. In particular, new anisotropic solutions are obtained from the well known static BTZ solution.

gr-qc↗

arXiv2018

Exact solutions of Einstein equations for anisotropic magnetic sources

In this work, we have obtained exact solutions of Einstein equations for static and axially symmetric magnetized matter, specifically in plane-symmetric and almost-plane symmetric cases. Although these solutions impose constraints on the components of the energy-momentum tensor, some physically interesting situations, like the magnetized vacuum, might be described. Plane-symmetric solutions in presence of a non-vanishing cosmological constant have remarkable features. In particular, the system can be driven continuously to the isotropic case by an appropriate tuning of the cosmological constant, sweeping the magnetic field from weak to strong magnetic field regimes. The role of the cosmological constant in magnetic collapse is discussed with an emphasis in the description of jets from compact objects. For illustrative purposes, specific calculations for a magnetized electron gas have been developed.

gr-qc↗

arXiv2018

A self-sustained traversable scale-dependent wormhole

A self--sustained traversable wormhole is obtained as a vacuum solution of a scale-dependent gravitational theory. Comparison with other approaches towards wormhole self--sustainability are presented, with emphasis on the running of the gravitational coupling and on a possible effective description of gravity near the Planck scale.

gr-qc↗

arXiv2018

Scale-dependent polytropic black hole

In the present work we study the scale--dependence of polytropic non-charged black holes in (3+1)-dimensional space--times assuming a cosmological constant. We allow for scale--dependence of the gravitational and cosmological couplings, and we solve the corresponding generalized field equations imposing the null energy condition. Besides, some properties, such as horizon structure and thermodynamics, are discussed in detail.

gr-qc↗

arXiv2017

A regular scale-dependent black hole solution

In this work, we present a regular black hole solution, in the context of scale-dependent General Relativity, satisfying the weak energy condition. The source of this solution is an anisotropic effective energy-momentum tensor which appears when the scale dependence of the theory is turned-on. In this sense, the solution can be considered as a semiclassical extension of the Schwarzschild one.

gr-qc↗

arXiv2017

Scale dependent three-dimensional charged black holes in linear and non-linear electrodynamics

In the present work we study the scale dependence at the level of the effective action of charged black holes in Einstein-Maxwell as well as in Einstein-power-Maxwell theories in (2+1)-dimensional spacetimes without a cosmological constant. We allow for scale dependence of the gravitational and electromagnetic couplings, and we solve the corresponding generalized field equations imposing the "null energy condition". Certain properties, such as horizon structure and thermodynamics, are discussed in detail.

hep-th↗

arXiv2017

A monoidal representation for linearized gravity

We propose an alternative representation for linear quantum gravity. It is based on the use of a structure that bears some resemblance to the Abelian loop representation used in electromagnetism but with the difference that space of extended object on which waves functions take values have a structure of commutative monoid instead of Abelian group. The generator of duality of the theory is realized in this representation and a geometrical interpretation is discussed.

hep-th↗

arXiv2016

Effective geometries and generalized uncertainty principle corrections to the Bekenstein-Hawking entropy

In this work we construct several black hole metrics which are consistent with the generalized uncertainty principle logarithmic correction to the Bekenstein-Hawking entropy formula. After preserving the event horizon at the usual position, a singularity at the Planck scale is found. Finally, these geometries are shown to be realized by certain model of nonlinear electrodynamics, which resembles previously studied regular black hole solutions.

gr-qc↗