arXiv subjects

Nora Breton

Publications and source records attributed to Nora Breton.

At least 19 recordsLinked to original sources

arXiv2026

Nonlinear electrodynamics in Kerr-Newman-NUT-$\Lambda$ spacetime: exact solutions, horizons, and energy conditions

We construct two exact nonlinear-electrodynamic generalizations of the Kerr-Newman-NUT-$\Lambda$ spacetime. Imposing alignment between the principal directions of the electromagnetic field and the metric tetrad reduces the Maxwell-Faraday sector to a pair of potentials constrained by a single integrability condition, the key equation. Within the polynomial aligned ansatz considered here, the key equation selects two admissible families, corresponding to electromagnetic potentials that are cubic and quartic polynomials. For each family the Einstein equations reduce to a single radial ordinary differential equation that gives a deformation of the Kerr-like radial metric function which is exactly solved. We derive the corresponding metrics, electromagnetic fields, stress tensors, horizon structure, and we analyze the associated energy conditions. The nonlinear sector breaks conformal invariance and, in the cubic family, can mimic an effective cosmological contribution. The explicit Lagrangians as functions of the electromagnetic invariants are obtained in selected static subsectors. The curvature invariants show that the nonlinear contribution does not remove the Kerr-like curvature singularity, while the solutions present the NUT axial conical singularity.

gr-qc↗

arXiv2026

Remarks on electrical Penrose process for magnetized Reissner-Nordstr\"om black hole

The energy extraction from a magnetized Reissner-Nordstr\"om black hole is analyzed within the framework of the electric Penrose mechanism. The presence of an external magnetic field induces an axisymmetric configuration and an ergosphere (the region where energy extraction is possible) arises, allowing for negative energy states even in an otherwise static spacetime. By analyzing the decay of particles at turning points of the radial motion, we derive the general expression for the efficiency of the process in terms of the metric coefficients and the electromagnetic potential. The resulting efficiencies are interpreted as Killing energy efficiencies associated with the local splitting process, while the escape of the positive energy fragment is treated as an additional effective-potential requirement. This formulation provides a direct criterion for identifying the ergoregions and we show that the magnetic field acts as a control parameter that governs both the configuration of the ergosphere and the efficiency of the process. In particular, analytical expressions for the critical magnetic fields that determine the onset and suppression of energy extraction are determined. Our results extend previous analysis of the electric Penrose process for magnetized configurations and clarify the role of the external field in enhancing or inhibiting energy extraction from charged black holes.

gr-qc↗

arXiv2025

Four-function generalization and separable structures of the Plebanski spacetime with sources

We determine a four-function generalization of the Plebanski spacetime, depending on three arbitrary functions of the radial coordinate, and one function on the angular coordinate. For the generalized Plebanski spacetime, we analyze the separability of the Hamilton--Jacobi equations, and the trajectories of charged test particles are derived from the motion constants. The Klein-Gordon equation separability is established and the Killing horizons are presented as well. Then we introduce a conformal factor to the Plebanski metric and discuss the conditions that preserve the separability. Finally we show a possible stress--energy tensor that may be the source of some of the generalized metrics.

gr-qc↗

arXiv2024

Comparative of light propagation in Born-Infeld, Euler-Heisenberg and ModMax nonlinear electrodynamics

We compare light propagation through an intense electromagnetic background as described by three different nonlinear electrodynamics: Born-Infeld (BI), Euler-Heisenberg (EH), and Modified Maxwell (MM). We use the concept of effective metric to determine the phase velocities of a propagating wave from the BI and EH nonlinear electrodynamics and use them to set constraints on the MM nonlinear parameter. In a second part of the paper, we consider the black hole solutions of the nonlinear electrodynamics coupled with General Relativity and determine the shadows cast by the static black holes. Confronting the observations of the shadows of M87$^*$ and Sagittarius A$^*$ with our theoretical results allows us to set restrictions on the nonlinear parameters.

gr-qc↗

arXiv2024

Nonlinear electromagnetic generalization of the Kerr-Newman solution with cosmological constant

We present the two exact solutions of the Einstein-Nonlinear electrodynamics equations that generalize the Kerr-Newman solution. We determined the generalized electromagnetic potentials using the alignment between the tetrad vectors of the metric and the eigenvectors of the electromagnetic field tensor. It turns out that there are only two possible nonlinear electromagnetic generalizations of the Kerr-Newman geometry, corresponding to different electromagnetic potentials. The new solutions possess horizons and satisfy physical energy conditions such that they can represent black holes with nonlinear electromagnetic charges, characterized by the parameters of mass, angular momentum, charge, and one nonlinear parameter; the nonlinear parameter resembles the effect of a cosmological constant, negative or positive, such that the solutions are asymptotically AdS or dS. The canonical form of the electromagnetic nonlinear energy-momentum tensor is analyzed in relation with the energy conditions; it is shown that the conformal symmetry is broken by the electromagnetic nonlinear matter; the corresponding nonlinear electromagnetic Lagrangian as a function of the coordinates is presented as well.

gr-qc↗

arXiv2024

Energy extraction from the Reissner-Nordstr\"om de Sitter black hole

The energy extraction from an electrostatic black hole by the decay or splitting of electrically charged particles is analyzed. We determine the energetic conditions that make the extraction process viable and present a general expression for the efficiency in terms of the parameters of the electrostatic black hole and the decaying particles. We also examine the conditions that optimize the efficiency of the extraction process. We analyze two particular cases, the first one is the extraction process from a Reissner Nordstr\"om black hole, for charged test particles with nonvanishing angular momentum; the second one and more interesting corresponds to the energy extraction from a Reissner Nordstr\"om de Sitter black hole. For the latter there are two regions where the energy extraction is possible, the generalized ergosphere and a cosmological ergosphere induced by the cosmological horizon. Under certain conditions the two ergospheres get connected and cover the whole region between the event horizon and the cosmological horizon, and therefore the energy extraction is possible at any point in the vicinity of the black hole. Moreover, the efficiency of the energy extraction can be the same for different break up points and also there is the possibility of a different efficiency for the same break up point. The conditions that maximize the efficiency are determined as well.

gr-qc↗

arXiv2023

Light Propagation in the vicinity of the ModMax black hole

ModMax is a nonlinear electrodynamics theory with the same symmetries as Maxwell electrodynamics. Static spherically symmetric solutions have been derived by coupling ModMax electrodynamics with the Einstein equations, which can represent a black hole. In this paper, we analyze light propagation in the vicinity of the ModMax black hole. We determine birefringence, light trajectories, deflection, redshifts, as well as the shadow of the black hole using the effective or optical metric to determine the optical paths of light; comparison is done with the corresponding effects in the neighborhood of the Reissner-Nordstrom black hole, that is the solution to the Einstein-Maxwell equations.

gr-qc↗

arXiv2022

Motion of the charged test particle in the spinning nonlinear electromagnetic black hole

In this paper the motion of charged and uncharged test particles in the rotating nonlinearly charged black hole is examined. Its asymptotics can be de Sitter or anti-de Sitter, depending on the value of the nonlinear parameter; consequently this BH can present one, two or three horizons, the third one being the cosmological horizon in the de Sitter case. Angular and radial test particle motions are analyzed and compared with its linear electromagnetic counterpart, the Kerr-Newman black hole (KN-BH). Several differences arise with the KN-BH, namely, the equatorial asymmetry is enhanced by the NLE field and for charged particles the access to one of the poles is forbidden; besides, a second circular orbit in the neighborhood of the external horizon appears; the presence of the nonlinear electromagnetic field increses the curvature producing bounded orbits closer to the horizon.

gr-qc↗

arXiv2022

Light propagating in a Born-Infeld background as seen by an accelerated observer

We study the propagation of light in the Born-Infeld (BI) background as seen by an accelerated observer. In a Born-Infeld electromagnetic field, light trajectories are governed by the null geodesics of the effective optical metric. The accelerated observer is in a Rindler frame, a situation that, according to the Einstein Equivalence Principle, is equivalent to being in a uniform gravitational field. The phase velocity of light propagating through a purely magnetic or electric BI background is determined as measured by the Rindler observer. The BI field and the acceleration of the frame have opposite effects on the propagating light: while the intense electric or magnetic BI background slows down the velocity of light, in the accelerated frame light may exceed its velocity in vacuum. We consider light propagating parallel or transversal to the acceleration direction of the Rindler frame. The redshift of light pulses sent from one Rindler observer to another, in the BI background, is calculated as well.

gr-qc↗

arXiv2020

Euler-Heisenberg waves propagating in a magnetic background

We derive the Euler-Heisenberg solutions that describe electromagnetic waves propagating through very intense uniform magnetic or electric background, with the effective metric approach. We first explore the case of a magnetic background: as a result of the interaction between the wave and the background there is birefringence and a longitudinal electric field component arises. The two phase velocities depend on the intensity of the external magnetic field and on the polarization of the wave; phase velocities can be slowed down up to the order of hundred thousandths for fields $B/B_{\rm cr} << 1$. The analogous study is done when the wave propagates through a uniform electric field. We then consider the situation when the background is in movement by means of a Lorentz boost, modeling then a magnetized flowing medium. We determined how this motion affects the speed of propagation of the electromagnetic wave, in this case the phase velocities depend on both the magnetic background and the direction and velocity of the boost.

hep-th↗

arXiv2020

Non-linear electrodynamics generalization of the rotating BTZ black hole

We obtain two exact solutions of Einstein gravity coupled to nonlinear electrodynamics (NLED) in $(2+ 1)$-dimensional Anti-de Sitter (AdS) spacetime. The solutions are characterized by the mass $M$, angular momentum $J$, cosmological constant or (anti) de Sitter parameter $Λ$, and an electromagnetic parameter $Q$, that is related to an electric field in the first solution and to a magnetic charge for the second solution. Depending on the range of the parameters, the solutions admit a charged rotating asymptotically AdS black hole (BH) interpretation or a charged rotating asymptotically AdS traversable wormhole (WH). If the electromagnetic field is turned off, the stationary Bañados-Teitelboim-Zanelli (BTZ) BH is recovered; in such a way that our BH-WH solutions are nonlinear charged generalizations of the stationary BTZ-BH. Moreover, in contrast to the BTZ metric, the derived AdS solutions are singular at certain radius $r_{s} \neq 0$, resembling the ring singularity of the Kerr-Newman spacetime; while if $Λ$ is positive the curvature invariants of the second solution are finite.

gr-qc↗

arXiv2019

(2+1)-dimensional Static Cyclic Symmetric Traversable Wormhole: Quasinormal Modes and Causality

In this paper we study a static cyclic symmetric traversable wormhole in $(2+1)-$dimensional gravity coupled to nonlinear electrodynamics in anti-de Sitter spacetime. The solution is characterized by three parameters: mass $M$, cosmological constant $Λ$ and one electromagnetic parameter, $q_α$. The causality of this spacetime is studied, determining its maximal extension and constructing then the corresponding Kruskal-Szekeres and Penrose diagrams. The quasinormal modes (QNMs) that result from considering a massive scalar test field in the wormhole background are determined by solving in exact form the Klein-Gordon equation; the effective potential resembles the one of a harmonic oscillator shifted from its equilibrium position and, consequently, the QNMs have a pure point spectrum.

gr-qc↗

arXiv2019

New exact traversable wormhole solution to the Einstein-scalar-Gauss-Bonnet Equations coupled to a power-Maxwell electrodynamics

We present a novel, exact, traversable wormhole (T-WH) solution for $(3+1)$-dimensional Einstein-scalar-Gauss-Bonnet theory (EsGB) coupled to a power-Maxwell nonlinear electrodynamics (NLED). The solution is characterized by two parameters, $\mathcal{Q}\!_{\rm e}$ and $\mathcal{Q}\!_{_{ \mathcal{S} }}$, associated respectively with the electromagnetic field and the scalar field. We show that for $\mathcal{Q}^2_{\rm e} - \mathcal{Q}\!_{_{ \mathcal{S} }}>0$ the solution can be interpreted as a traversable wormhole. In the general case, with non-vanishing electromagnetic field, the scalar-Gauss-Bonnet term (sGB) is the only responsible for the negative energy density necessary for the traversability. In the limiting case of vanishing electromagnetic field, the scalar field becomes a phantom one keeping the WH throat open and in this case the Ellis WH solution \cite{Ellis} is recovered.

gr-qc↗

arXiv2019

Black Hole-Wormhole transition in (2+1) Einstein -- anti-de Sitter Gravity Coupled to Nonlinear Electrodynamics

In this paper we present two results in $(2+1)$ gravity coupled to nonlinear electrodynamics. First it is determined the general form of the electromagnetic field tensor in $(2+1)$ gravity coupled to nonlinear electrodynamics in stationary cyclic spacetimes. Secondly, it is determined a family of exact solutions in $(2+1)$ gravity sourced by a nonlinear electromagnetic field. The solutions are characterized by five parameters: mass $M$, angular momentum $J$, cosmological constant $Λ$ and two electromagnetic charges, $q_α$ and $q_β$. Remarkably, the solution can be interpreted as a traversable wormhole, provided the fulfillment of certain inequalities by the characteristic parameters; fine tunning of the cosmological constant leads to an extreme black hole, whereas by switching off one of the electromagnetic charges, we obtain the Bañados-Teitelboim-Zanelli (BTZ) black hole.

gr-qc↗

arXiv2017

Quasinormal modes and absorption cross sections of Born-Infeld-de Sitter black holes

In this paper, we have studied QNM modes and absorption cross sections of Born-Infeld-de Sitter black holes. WKB approximation is employed to compute the QNM modes of massless scalar fields. We have also used null geodesics to compute quasi-normal modes in the eikonal approximation. In the eikonal limit QNMs of black holes are determined by the parameters of the circular null geodesics. Unstable circular null orbits are derived from the effective metric which is obeyed by light rays under the influence of a nonlinear electromagnetic field. Comparison is shown with the QNM of the linear electromagnetic counterpart, the Reissner-Nordström black hole. Furthermore, the null geodesics are employed to compute the absorption cross sections in the high frequency limit via the sinc approximation.

gr-qc↗

arXiv2016

Energy Extraction from the Einstein-Born-Infeld Black Hole

The energy extraction from a Einstein-Born-Infeld (EBI) black hole is addressed determining the extension of the ergosphere as well as the extractable energy using the irreducible mass concept. These results are compared with the Reissner-Nordstrom (RN) ones; RN is the linear electromagnetic counterpart of the BI black hole. It turns out that for a fixed charge Q, more energy can be extracted from the RN black hole than from the EBI one. The extreme case is investigated as well, presenting remarkable features, for instance that more energy can be extracted from extreme EBI black holes than from extreme RN, however, extreme EBI black holes lack of a linear electromagnetic black hole limit.

gr-qc↗

arXiv2008

Some properties of evolving wormhole geometries within nonlinear electrodynamics

In this paper we review some properties for the evolving wormhole solution of Einstein equations coupled with nonlinear electrodynamics. We integrate the geodesic equations in the effective geometry obeyed by photons; we check out the weak field limit and find the traversability conditions. Then we analyze the case when the lagrangian depends on two electromagnetic invariants and it turns out that there is not a more general solution within the assumed geometry.

gr-qc↗

arXiv2007

Nonlinear Electrodynamics and black holes

It is addressed the issue of black holes with nonlinear electromagnetic field, focussing mainly in the Born-Infeld case. The main features of these systems are described, for instance, geodesics, energy conditions, thermodynamics and isolated horizon aspects. Also are revised some black hole solutions of alternative nonlinear electrodynamics and its inconveniences.

hep-th↗