Narrow Results

It is well known that the Smarr formula does not hold for black holes in nonlinear electrodynamics. The main reason for this is the fact that the trace of the energy–momentum tensor for nonlinear electrodynamics does not vanish as it is for Maxwell’s electrodynamics. Starting from the Komar integral, we derived a new Smarr-type formula for spherically symmetric static electrically charged black hole solutions in nonlinear electrodynamics. We show that this general formula is in agreement with some that are obtained for black hole solutions with nonlinear electrodynamics.

Let a particle move in the flat spacetime under the action of the electric potential. If it decays to two fragments, the energy of debris can be larger than the original energy and, moreover, the efficiency of such a process can be unbounded. This effect can be considered as a limit of the Denardo–Ruffini process near the Reissner–Nordström black hole when the gravitational constant and/or black hole mass tend to zero. There are scenarios in which the energy of debris at infinity is much larger than the initial one. Comparison with other close but distinct effects is discussed.

We investigate the dynamical motion of test particles and accretion processes around spherically symmetric charged black hole. We first show the derivation of the Paczyňski–Wiita (PW) potential for any spherically symmetric spacetime and present analytical form of the PW potential in the Reissner–Nordström (RN) spacetime and the RN-type spacetime. We study the dependence of the characteristic orbits of test (neutral and charged) particles around a charged black hole from two main parameters, namely, charge of RN black hole and the interaction of charged particle with the external electromagnetic field of the black hole and present graphical trajectories of test particles around the black hole. It is shown that with increasing the absolute value of interaction parameter, $\left|qQ\right|$, the innermost stable circular orbit (ISCO) radius for charged particle always increases. It is also shown that the energy efficiency for a charged particles can reach up to $60\%$ in the presence of an external charged black hole, while for neutral particles it can reach up to $8\%$ for neutral particles. The capture cross-section of the photon is by the charged black and the optical appearance of the thin accretion disk around the charged black. Finally, we have studied the flux energy and the thermal spectrum of the accretion disk consisting of the polytropic gas, around the charged black hole.

This paper probes the geodesic structure of spherically symmetric charged black holes using modified theory of gravity. We explore the geodesic structures of different black holes in the background of Palatini $f(R)$ theory as well as Eddington-inspired Born–Infeld gravity. We have examined the stability of orbits with the analysis of effective potential. The impacts of modified gravity on particle dynamics specially the circular orbits, the deflection angle and trajectory followed by lightlike as well as for timelike particles are scrutinized. We find that the orbits are more stable for the large values of charge and Born–Infeld parameter.

We investigate a new model of nonlinear electromagnetic field coupled with the gravitation field. The black hole solution is obtained possessing the asymptotic Reissner–Nordström solution. The electric field has the finite value at the origin and there are not singularities.

In this paper, the Einstein-nonlinear electromagnetic theory has been studied in the four-dimensional de Sitter (dS) and anti-de Sitter (AdS) spacetimes. A new class of nonlinearly charged A(dS) black hole solution, in the presence of quadratically-extended Maxwell field, has been obtained and the thermodynamical properties have been analyzed. The black hole entropy, temperature and electric potential have been calculated, making use of the geometric methods. Through a Smarr mass formula the black hole mass has been written as a function of the complete set of extensive parameters (i.e. charge and entropy). It has been found that the intensive parameters (i.e. electric potential and temperature) obtained from the mass formula coincide with their values obtained from geometric approaches. It confirms the validity of the first law of black hole thermodynamics. A black hole stability analysis has been performed from the canonical ensemble approach, regarding the black hole heat capacity with the black hole charge as a constant. The points of type one and type two phase transitions, and the ranges at which the new charged A(dS) black holes are locally stable have been determined. Also, for the new charged black holes to be physically reasonable, their charge has been restricted to some specific ranges.

This paper provides an extension for Hawking temperature of Reissner–Nordström-de Sitter (RN-DS) black hole (BH) with global monopole as well as $5$D charged black hole. We consider the black holes metric and investigate the effects of quantum gravity ($\alpha$) on Hawking radiation. We investigate the charged boson particles tunneling through the horizon of black holes by using the Hamilton–Jacobi ansatz phenomenon. In our investigation, we study the quantum radiation to analyze the Lagrangian wave equation with generalized uncertainty principle and calculate the modified Hawking temperatures for black holes. Furthermore, we analyze the charge and correction parameter effects on the modified Hawking temperature and examine the stable and unstable condition of RN-DS BH with global monopole as well as $5$D charged black hole.

We investigate possible end-points of the superradiant instability for a charged black hole with a reflecting mirror. By considering a fully coupled system of gravity and a charged scalar field, hairy black hole solutions are obtained. The linear stability of these black hole solutions is studied.

We explore the connection between the distribution of particles spontaneously produced from an electric field or black hole and the vacuum persistence, twice the imaginary part of the one-loop effective action. Employing the reconstruction conjecture, we find the effective action for the Bose-Einstein or Fermi-Dirac distribution. The Schwinger effect in AdS₂ is computed via the phase-integral method in the static coordinates. The Hawking radiation and Schwinger effect of a charged black hole is rederived and interpreted via the phase-integral. Finally, we discuss the relation between the vacuum persistence and the trace or gravitational anomalies.