Nonlinear Electrodynamics Field Research Articles

Thermodynamics of 4-dimensional charged black holes in Brans-Dicke-Born-Infeld gravity theory

In this work, the charged black hole solution to the Brans-Dicke gravity theory in the presence of the nonlinear electrodynamics has been investigated. To simplify the field equations, a suitable conformal transformation has been used which transforms the Brans-Dicke-Born-Infeld Lagrangian to that of Einstein-dilaton theory with new nonlinear electrodynamics field. A new class of 4-dimensional black hole solution has been constructed out as the exact solution to the Brans-Dicke theory in the presence of the Born-Infeld nonlinear electrodynamics. The physical properties of the solutions have been studied. The black hole charge and temperature have been calculated making use of the Gauss’s law and the concept of surface gravity, respectively. Also, the black hole mass and entropy have been obtained from geometrical methods. Through a Smarr-type mass formula as a function of the black hole charge and entropy the black hole temperature and electric potential, as the intensive parameters conjugate to the black hole entropy and charge, have been calculated.

Membrane paradigm and holographic DC conductivity for nonlinear electrodynamics

Membrane paradigm is a powerful tool to study properties of black hole horizons. We first explore the properties of the nonlinear electromagnetic membrane of black holes. For a general nonlinear electrodynamics field, we show that the conductivities of the horizon usually have off-diagonal components and depend on the normal electric and magnetic fields on the horizon. Via the holographic duality, we find a model-independent expression for the holographic DC conductivities of the conserved current dual to a probe nonlinear electrodynamics field in a neutral and static black brane background. It shows that these DC conductivities only depend on the geometric and electromagnetic quantities evaluated at the horizon. We can also express the DC conductivities in terms of the temperature, charge density and magnetic field in the boundary theory, as well as the values of the couplings in the nonlinear electrodynamics at the horizon.

Falsifying cosmological models based on a non-linear electrodynamics

Recently, the nonlinear electrodynamics (NED) has been gaining attention to generate primordial magnetic fields in the Universe and also to resolve singularity problems. Moreover, recent works have shown the crucial role of the NED on the inflation. This paper provides a new approach based on a new model of NED as a source of gravitation to remove the cosmic singularity at the big bang and explain the cosmic acceleration during the inflation era on the background of stochastic magnetic field. Also, we found a realization of a cyclic Universe, free of initial singularity, due to the proposed NED energy density. In addition, we explore whether a NED field without or with matter can be the origin of the late-time acceleration. For this we obtain explicit equations for H(z) and perform a MCMC analysis to constrain the NED parameters by using 31 observational Hubble data (OHD) obtained from cosmic chronometers covering the redshift range 0< z < 1.97; and with the joint-light-analysis (JLA) SNIa compilation consisting in 740 data points in the range 0.01<z<1.2. All our constraints on the current magnetic field give B_{0}sim 10^{-31}mathrm {cm^{-1}}, which are larger than the upper limit 10^{-33}mathrm {cm^{-1}} by the Planck satellite implying that NED cosmologies could not be suitable to explain the Universe late-time dynamics. However, the current data is able to falsify the scenario at late times. Indeed, one is able to reconstruct the deceleration parameter q(z) using the best fit values of the parameters obtained from OHD and SNIa data sets. If the matter component is not included, the data sets predict an accelerated phase in the early Universe, but a non accelerated Universe is preferred in the current epoch. When a matter component is included in the NED cosmology, the data sets predict a q(z) dynamics similar to that of the standard model. Moreover, both cosmological data favor up to 2sigma confidence levels an accelerating expansion in the current epoch, i.e., the Universe passes of a decelerated phase to an accelerated stage at redshift sim 0.6. Therefore, although the NED cosmology with dust matter predict a value B_{0} higher than the one measured by Planck satellite, it is able to drive a late-time cosmic acceleration which is consistent with our dynamical systems analysis and it is preferred by OHD and SNIa data sets.

Effects of Exponential Nonlinear Electrodynamics and External Magnetic Field on Holographic Superconductors

We investigate the effects of an external magnetic field as well as exponential nonlinear electrodynamics on the properties of s-wave holographic superconductors. Our strategy for this study is the matching method, which is based on the match of the solutions near the horizon and on the boundary at some intermediate point. When the magnetic field is turned off, we obtain the critical temperature as well as the condensation operator and show that the critical exponent is still 1/2, which is the universal value in the mean field theory. Then, we turn on the magnetic field and obtain the critical magnetic field, B c , in order to study its behavior in terms of the temperature. Interestingly enough, we find that in the presence of exponential nonlinear electrodynamics, the critical temperature decreases, while the critical magnetic field increases compared to the Maxwell case. We also observe that the critical magnetic field increases with increasing the nonlinear parameter b.

Black holes in nonlinear electrodynamics: Quasinormal spectra and parity splitting

We discuss the quasi-normal oscillations of black holes which are sourced by a nonlinear electrodynamic field. While previous studies have focused on the computation of quasi-normal frequencies for the wave or higher spin equation on a fixed background geometry described by such black holes, here we compute for the first time the quasi-normal frequencies for the coupled electromagnetic-gravitational linear perturbations. To this purpose, we consider a parametrized family of Lagrangians for the electromagnetic field which contains the Maxwell Lagrangian as a special case. In the Maxwell case, the unique spherically symmetric black hole solutions are described by the Reissner-Nordstr\"om family and in this case it is well-known that the quasi-normal spectra in the even- and odd-parity sectors are identical to each other. However, when moving away from the Maxwell case, we obtain deformed Reissner-Nordstr\"om black holes, and we show that in this case there is a parity splitting in the quasi-normal mode spectra. A partial explanation for this phenomena is provided by considering the eikonal (high-frequency) limit.

Thermodynamic geometry and thermal stability ofn-dimensional dilaton black holes in the presence of logarithmic nonlinear electrodynamics

In this paper, we construct a new class of black hole solutions which is coupled to the logarithmic nonlinear electrodynamics in the context of dilaton gravity. We consider an $n$-dimensional action in which gravity is coupled to the logarithmic nonlinear electrodynamics field and a scalar dilaton field to obtain the equations of motion of the gravitational, dilaton and electromagnetic fields. This leads to finding a new class of $n$-dimensional static and spherically symmetric black hole solutions in the presence of two Liouville-type dilaton potentials. The asymptotic behavior of these solutions is neither flat nor (anti-)de Sitter [(A)dS], and in the limiting case where the nonlinear parameter $\ensuremath{\beta}$ goes to infinity, our solutions reduce to the black holes of Einstein-Maxwell-dilaton gravity in higher dimensions. Thermodynamic quantities such as mass, temperature, electric potential and entropy are also computed, and it is shown that they agree with the first law of thermodynamics. Furthermore, we find that for small values of the electric charge parameter $q$, and the dilaton coupling constant $\ensuremath{\alpha}$, as well as small dimension $n$, the solutions are thermally stable. By increasing $n$, the region of stability stands for smaller values of $\ensuremath{\alpha}$ independent of $q$. Finally, we use the method of thermodynamical geometry and find the phase transition points by calculating the Ricci scalar of a thermodynamic metric.

Einstein–Born–Infeld black holes with a scalar hair in three dimensions

We present black hole solutions in (2+1)-dimensional Einstein’s theory of gravity coupled with Born–Infeld (BI) nonlinear electrodynamic and a massless self-interacting scalar field. The model has five free parameters: mass [Formula: see text], cosmological constant [Formula: see text], electric [Formula: see text] and scalar [Formula: see text] charges and BI parameter [Formula: see text]. To attain exact solution for such a highly nonlinear system we adjust, i.e. finely tune, the parameters of the theory with the integration constants. In the limit [Formula: see text], we recover the results of Einstein–Maxwell–Scalar theory, obtained before. The self-interacting potential admits finite minima apt for the vacuum contribution. Hawking temperature of the model is investigated versus properly tuned parameters. By employing this tuned-solution as basis, we obtain also a dynamic solution which in the proper limit admits the known solution in Einstein gravity coupled with self-interacting scalar field. Finally, we establish the equations of a general scalar–tensor field coupled to nonlinear electrodynamics (NED) field in 2+1 dimensions without searching for exact solutions.

Magnetically charged regular black hole in a model of nonlinear electrodynamics

We obtain a magnetically charged regular black hole in general relativity. The source to the Einstein field equations is nonlinear electrodynamic field in a physically reasonable model of nonlinear electrodynamics (NED). “Physically” here means the NED model is constructed on the basis of three conditions: the Maxwell asymptotic in the weak electromagnetic field limit; the presence of vacuum birefringence phenomenon; and satisfying the weak energy condition (WEC). In addition, we analyze the thermodynamic properties of the regular black hole in two ways. According to the usual black hole thermodynamics, we calculate the heat capacity at constant charge, from which we know the smaller black hole is more stable. We also employ the horizon thermodynamics to discuss the thermodynamic quantities, especially the heat capacity at constant pressure.

Dilaton black holes coupled to nonlinear electrodynamic field

The theory of nonlinear electrodynamics has got a lot of attentions in recent years. It was shown that Born-Infeld nonlinear electrodynamics is not the only modification of the linear Maxwell's field which keeps the electric field of a charged point particle finite at the origin, and other type of nonlinear Lagrangian such as exponential and logarithmic nonlinear electrodynamics can play the same role. In this paper, we generalize the study on the exponential nonlinear electrodynamics by adding a scalar dilaton field to the action. By suitably choosing the coupling of the matter field to the dilaton field, we vary the action and obtain the corresponding field equations. Then, by making a proper ansatz, we construct a new class of charged dilaton black hole solutions coupled to the exponential nonlinear electrodynamics field in the presence of two Liouville-type potentials for the dilaton field. Due to the presence of the dilaton field, the asymptotic behavior of these solutions are neither flat nor (A)dS. In the limiting case where the nonlinear parameter $\beta^2$ goes to infinity, our solution reduces to the Einstein-Maxwell dilaton black holes. We obtain the mass, temperature, entropy and electric potential of these solutions. We also study the behaviour of the electric field as well as the electric potential of these black holes near the origin. We find that the electric field has a finite value \textit{near} the origin, which is the same as the electric field of Born-Infeld nonlinear electrodynamics, but it can diverge exactly at $r=0$ depending on the model parameters. We also investigate the effects of the dilaton field on the behaviour of the electric field and electric potential. Finally, we check the validity of the first law of black hole thermodynamics on the black hole horizon.

Charge screening by thin shells in a 2+1-dimensional regular black hole

We consider a particular Bardeen black hole in 2+1-dimensions. The black hole is sourced by a radial electric field in non-linear electrodynamics (NED). The solution is obtained anew by the alternative Hamiltonian formalism. For $r\rightarrow \infty $ it asymptotes to the charged BTZ black hole. It is shown that by inserting a charged, thin-shell (or ring) the charge of the regular black hole can be screened from the external world.

Stability of Thin-Shell Wormholes in Nonlinear Electrodynamics

In this paper, we construct thin-shell wormholes by applying the cut and paste procedure to a regular charged black hole in nonlinear electrodynamics field. We discuss different physical aspects of wormholes such as, the possible equation of state to matter shell, attractive or repulsive nature of wormhole and total amount of exotic matter required. The thin-shell equation of motion with and without cosmological constant is also investigated under linearized perturbation. Finally, we explore the stability regions interpreted by the parameter β (speed of sound) and conclude that there are realistic stability regions for some fixed values of parameters.

Role of Entropy-Corrected New Agegraphic Dark Energy in Hořava-Lifshitz Gravity

In this work, we have considered the entropy-corrected new agegraphic dark energy (ECNADE) model in Horava-Lifshitz gravity in FRW universe. We have discussed the correspondence between ECNADE and other dark energy models such as DBI-essence,Yang-Mills dark energy, Chameleon field, Non-linear electrodynamics field and hessence dark energy in the context of Horava-Lifshitz gravity and reconstructed the potentials and the dynamics of the scalar field theory which describe the ECNADE.

Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics

The first regular exact black hole solution in general relativity is presented. The source is a nonlinear electrodynamic field satisfying the weak energy condition, which in the limit of weak field becomes the Maxwell field. The solution corresponds to a charged black hole with $|q|\ensuremath{\le}{2s}_{c}m\ensuremath{\approx}0.6m$, having the metric, the curvature invariants, and the electric field regular everywhere.

Generation of multipole moments by external field in Born-Infeld nonlinear electrodynamics

The mechanism for the generation of multipole moments due to an external field is presented for the Born-Infeld charged particle. The `polarizability coefficient' for arbitrary l-pole moment is calculated. It turns out that , where and b is the Born-Infeld nonlinearity constant. Some physical implications are considered.

Generation of a dipole moment by external field in Born-Infeld non-linear electrodynamics

The mechanism for generation of a dipole moment due to an external field is presented for the Born-lnfeld charged particle. The ‘polarizability coefficient’ is calculated: κ = 1.85407 r 0 3, where r 0 : = | e | / 4 π b and b is the Bom-Infeld non-linearity constant.