No Arabic abstract
In the present article we study the Inverse Electrodynamics Model. This model is a gauge and parity invariant non-linear Electrodynamics theory, which respects the conformal invariance of standard Electrodynamics. This modified Electrodynamics model, when minimally coupled to General Relativity, is compatible with static and spherically symmetric Reissner-Nordstrom-like black-hole solutions. However, these black-hole solutions present more complex thermodynamic properties than their Reissner-Nordstrom black-hole solutions counterparts in standard Electrodynamics. In particular, in the Inverse Model a new stability region, with both the heat capacity and the free energy negative, arises. Moreover, unlike the scenario in standard Electrodynamics, a sole transition phase is possible for a suitable choice in the set of parameters of these solutions.
We study black holes produced by the collapse of a spherically symmetric charged scalar field in asymptotically flat space. We employ a late time expansion and show decaying fluxes of radiation through the event horizon imply the black hole must contain a null singularity on the Cauchy horizon and a central spacelike singularity.
In this work we address the study of null geodesics in the background of Reissner-Nordstrom Anti de Sitter black holes. We compute the exact trajectories in terms of elliptic functions of Weierstrass, obtaining a detailed description of the orbits in terms of charge, mass and the cosmological constant. The trajectories of the photon are classified using the impact parameter.
Reissner-Nordstrom Anti-de Sitter (RNAdS) black holes are unstable against the charged scalar field perturbations due to the well-known superradiance phenomenon. We present the time domain analysis of charged scalar field perturbations in the RNAdS black hole background in general dimensions. We show that the instabilities of charged scalar field can be explicitly illustrated from the time profiles of evolving scalar field. By using the Prony method to fit the time evolution data, we confirm the mode that dominates the long time behavior of scalar field is in accordance with the quasinormal mode from the frequency domain analysis. The superradiance origin of the instability can also be demonstrated by comparing the real part of the dominant mode with the superradiant condition of charged scalar field. It is shown that all the unstable modes are superradiant, which is consistent with the analytical result in the frequency domain analysis. Furthermore, we also confirm there exists the rapid exponential growing modes in the RNAdS case, which makes the RNAdS black hole a good test ground to investigate the nonlinear evolution of superradiant instability.
The Joule-Thomson expansion is studied for Reissner-Nordstrom-Anti-de Sitter black holes with cloud of strings and quintessence, as well as its thermodynamics. The cosmological constant is treated as thermodynamic pressure, whose conjugate variable is considered as the volume. The characteristics of the Joule-Thomson expansion are studied in four main aspects with the case of $omega=-1$ and $omega=-frac{2}{3}$, including the Joule-Thomson coefficient, the inversion curves, the isenthalpic curves and the ratio between $T_{i}^{min}$ and $T_{c}$. The sign of the Joule-Thomson coefficient is possible for determining the occurrence of heating or cooling. The scattering point of the Joule-Thomson coefficient corresponds to the zero point of the Hawking temperature. Unlike the van der Waals fluids, the inversion curve is the dividing line between heating and cooling regions, above which the slope of the isenthalpic curve is positive and cooling occurs, and the cooling-heating critical point is more sensitive to $Q$. Concerning the ratio $frac{T_{i}^{min}}{T_{c}}$, we calculate it separately in the cases where only the cloud of strings, only quintessence and both are present.
We investigate spherically symmetric, steady state, adiabatic accretion onto a Tangherlini-Reissner-Nordstrom black hole in arbitrary dimensions by using $D$-dimensional general relativity. We obtain basic equations for accretion and determine analytically the critical points, the critical fluid velocity, and the critical sound speed. We lay emphasis on the condition under which the accretion is possible. This condition constrains the ratio of mass to charge in a narrow limit, which is independent of dimension for large dimension. This condition may challenge the validity of the cosmic censorship conjecture since a naked singularity is eventually produced as the magnitude of charge increases compared to the mass of black hole.