Dariescu

The present paper deals with the Schwarzschild black holes with quintessence whose geometry is sourced by a magnetic monopole in the context of non-linear electrodynamics. After briefly discussing the timelike geodesics and radial motion, a special attention is given to the Dirac equation. In the massless case, the radial function is expressed in terms of Heun general functions. The outgoing wave solutions are used to compute the Hawking temperatures on the horizons and the corresponding heat capacities.

For the static spherically symmetric dilatonic black hole described by the Gibbons-Maeda-Garfinkle-Horowitz-Strominger geometry, we analyze the timelike trajectories for charged particles. Both cases of an electric black hole and a magnetic one are considered. Finally, we are obtaining the solution to the Klein-Gordon equation in terms of Heun confluent functions and the corresponding energy spectrum. A special attention is given to the role of the dilaton parameter.

In this work we analyze the motion of charged particles in the background of the Kiselev geometry, which is considered here as an exact solution in the context of power-Maxwell electrodynamics. As it is well known, one can use either an electric ansatz or a magnetic one for the nonlinear electromagnetic field. We study the motion of an electrically charged particle for an electrically charged black hole and also for a magnetically charged black hole. In the second case the motion is restricted to Poincaré cones of various angles, as expected.

We present two solution-generating techniques, which are direct generalizations of certain Ehlers-Harrison transformations in the Ernst formalism, while adapted to work in presence of an anisotropic fluid source with axial symmetry. Based on these procedures, we were able to construct the electrically charged and the magnetized solution for any static axially symmetric geometry, which is sourced in general by an anisotropic fluid described by a nondiagonal anisotropic stress-energy tensor. As our main examples we derived and analyzed two new exact solutions with axial symmetry that describe the electrically charged Zipoy-Vorhees interior solution as well as the magnetized Zipoy-Vorhees interior solution, and presented some of their properties. As further examples of our solution-generating techniques we show how to derive two new solutions describing the electrically charged version of the Bowers and Liang …

Recently, Cardoso et al. [14] constructed an exact solution of Einstein's equations that describes a supermassive black hole immersed into a dark matter halo. In this work use a solution-generating technique, which is a direct generalization of some of the Ehlers-Harrison transformation in the Ehlers formalism in order to construct in an exact analytical form the charged version of the Cardoso et al. solution. We describe some of its physical properties and, finally, we also present its magnetized version.

In this work we reconsider the solution describing black holes surrounded by a quintessencelike fluid. This geometry was introduced by Kiselev in 2003 and its physical source was originally modeled by an anisotropic fluid. We show that the Kiselev geometry is actually an exact solution of the Einstein equations coupled to nonlinear electrodynamics. More specifically, we show that the Kiselev geometry becomes an exact solution in the context of power-Maxwell electrodynamics, using either an electric ansatz or a magnetic one. In both cases the physical source can be modeled by a power-Maxwell Lagrangian, albeit with different powers corresponding to the electric or the magnetic charges. We briefly investigate the motion of charged particles in this geometry. Finally, we give the proper interpretation of the black-hole thermodynamics in this context. Similarly to the Schwarzschild-de Sitter case, we note the …

Abstract The Ellis-Bronnikov solution provides a simple toy model for the study of various aspects of wormhole physics. In this work we solve the Klein-Gordon equation in this background and find an exact solution in terms of Heun's function. This may describe ‘scalar clouds’(i. e. localized, particle-like configuration) or scalar waves. However, in the former case, the radial derivative of the scalar field is discontinuous at the wormhole's throat (except for the spherical case). This pathology is absent for a suitable scalar field self-interaction, and we provide evidence for the existence of spherically symmetric and spinning Q-balls in a Ellis-Bronnikov wormhole background.

In order to explain the flat galaxy’s rotation curves, in the present work, we are employing a modified Schwarzschild exterior solution for describing the regions outside the core of spiral galaxies. In this respect, the explicit form of the timelike geodesics and the effective potential are derived. The final part of the paper is devoted to the Klein–Gordon equation for relativistic particles evolving in this spacetime. Analytical solutions can be obtained only in the long-range approximation or in the massless case.

The present paper is using a general relativistic approach to deal with the well-known problem of flat galaxy’s rotation curves. The steep increase of the circular velocity in the core is obtained by using the Schwarzschild interior solution. The corresponding Gordon equation is satisfied by Heun general functions. On the other hand, at large distances from the core, one can employ a newly proposed metric, describing the Schwarzschild black hole immersed in dark matter. Analytic solutions to the Gordon equation can be obtained only in particular cases.

The present paper deals with the Mannheim-Kazanas metric which is supposed to offer a reliable explanation on the observed galaxy rotation curves. The effective potential and the geodesic deviations are discussed. For a particular form of the metric, depending only on two parameters, the Gordon equation for massless bosons is satisfied by the Heun general functions. A special attention is given to the physically important local Minkowskian region, which has no analogue in the Schwarzschild case.

We are considering the spacetime described by the metric proposed by Mannheim and Kazanas. The effective potential and the circular orbits are discussed. The rotational velocity derived from the geodesics equation agrees with the observed flat galactic rotation curves. Finally, solutions to the Gordon equation for massless bosons evolving in this spacetime are obtained in terms of Heun general functions.

By employing a pseudoorthonormal coordinate-free approach, the Dirac equation for particles in the Kerr–Newman spacetime is separated into its radial and angular parts. In the massless case to which a special attention is given, the general Heun-type equations turn into their confluent form. We show how one recovers some results previously obtained in literature, by other means.

In the present paper, we are developing an analytical method for solving the time-dependent Kompaneets equation in its generalized form. The technique is generalizing the Dubinov and Kitayev method. In the particular case of a low photon number density, for the corresponding linear equation, the solutions are expressed in terms of Heun functions.

We study the solutions of the Dirac equation in the background of a static black string in four dimensions. We point out the presence of an additional term which was omitted in previous studies in the literature. We show how the Dirac equation can be separated for massive fermions. Finally, in the massless case, we obtain an exact solution of the Dirac equation in terms of the general Heun functions.

We start our study by writing down the Klein–Gordon equation for charged bosons evolving in magnetars described by spherically prolate metrics. For massless particles, the variables can be separated and the radial equation can be solved for physically interesting cases of metric functions. For the interior Schwarzschild solution immersed in a magnetic universe, the corresponding wave function is expressed in terms of the general Heun functions. For the outer region of the magnetar, one has to consider besides the magnetic field, an electric intensity. A general relation between the metric functions is derived. For , this is leading to the Schwarzschild exterior electro-magnetized metric and to confluent Heun functions, as solutions to the corresponding Klein–Gordon equation.

Employing a pseudo-orthonormal coordinate-free approach, we write down the Dirac equation in spacetimes with static general prolate metrics. As examples, we consider the electrically charged C-metric, the vacuum C-metric, the Reissner–Nordström and Schwarzschild spacetimes and the BBMB black hole and show that the solutions to the Dirac equations for particles in these spacetimes can be derived in terms of Heun’s general functions and their confluent and double confluent forms. By imposing boundary conditions to the radial solutions, the so-called resonant frequencies are obtained.