B. Malakolkalami | Searcharxiv

arXiv2024

Real particle geodesics and thermodynamics of a black hole in Regular Schwarzschild-Anti de Sitter space-time

Regular Schwarzschild Anti-de-Sitter (RSch-AdS) spacetime, which is a maximally symmetric and Lorentzian manifold of negative curvature, is a solution of Einstein's field equations with a negative cosmological constant and a matter source with a Gaussian distribution. Studying of black hole (BH) in such a spacetime, known as RSch-AdS black hole, can be instructive from various aspects and lead to a better understanding of them. In this regard, geodesics of real particles around RSch-AdS black holes and RSch-AdS thermodynamics of BH are two important issues that we are going to evaluate in this research. For this purpose, we first obtain the geodesics of real particles based on the changes in the values of effective parameters such as mass distribution, angular momentum and cosmological constant numerically according to boundary conditions and interpret their behavior. Second, using the laws of thermodynamics, some aspects of BH, defined in this spacetime, such as temperature, entropy, heat capacity and Gibbs free energy are studied and discussed

gr-qc↗

arXiv2017

Geodesics around oscillatons made of exponential scalar field potential

Oscillatons are spherically symmetric solutions to the Einstein Klein Gordon (EKG) equations for soliton stars made of real time dependent scalar fields. These equations are non singular and satisfy flatness conditions asymptotically with periodic time dependency. In this paper, we investigate the geodesic motion of particles moving around an oscillaton related to a time dependent scalar field. Bound orbital is found for these particles under the condition of particular values of angular momentum L and initial radial position. We discuss this topic for an exponential scalar field potential which could be of the exponential form with a scalar field and investigate whether the radial coordinates of such particles oscillate in time or not and thereby we could predict the corresponding oscillating period as well as amplitude. It is necessary to recall, in general relativity, a geodesic generalizes the notion of a straight line to curved space time. Importantly, the world line of a particle free from all external, non gravitational forces, is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic. In general relativity, gravity can be regarded as not a force but a consequence of a curved space time geometry where the source of curvature is the stress energy tensor (representing matter, for instance). Thus, for example, the path of a planet orbiting around a star is the projection of a geodesic of the curved 4D space time geometry around the star onto 3D space.

gr-qc↗