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Cristina Blaga

Publications and source records attributed to Cristina Blaga.

9 recordsLinked to original sources
arXiv2026

Jacobi stability of circular orbits around conformally invariant Weyl gravity black holes

Weyl conformal gravity was originally proposed in the early twentieth century as an attempt to unify gravitation and electromagnetism. Since 1989, renewed interest in this fourth-order theory of gravity has emerged following the discovery of several exact black hole solutions. In this work, we investigate the timelike circular geodesics of a spherically symmetric Weyl black hole. The effective potential, the circular geodesics and their Jacobi and Lyapunov stability are discussed. Our analysis provides new insights into the stability properties of Weyl black holes and the role of the free parameters appearing in their solutions.

gr-qc↗
arXiv2023

Jacobi and Lyapunov stability analysis of circular geodesics around a spherically symmetric dilaton black hole

We analyze the stability of the geodesic curves in the geometry of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole, describing the space time of a charged black hole in the low energy limit of the string theory. The stability analysis is performed by using both the linear (Lyapunov) stability method, as well as the notion of Jacobi stability, based on the Kosambi-Cartan-Chern theory. Brief reviews of the two stability methods are also presented. After obtaining the geodesic equations in spherical symmetry, we reformulate them as a two-dimensional dynamic system. The Jacobi stability analysis of the geodesic equations is performed by considering the important geometric invariants that can be used for the description of this system (the nonlinear and the Berwald connections), as well as the deviation curvature tensor, respectively. The characteristic values of the deviation curvature tensor are specifically calculated, as given by the second derivative of effective potential of the geodesic motion. The Lyapunov stability analysis leads to the same results. Hence, we can conclude that in the particular case of the geodesic motion on circular orbits in the Gibbons-Maeda-Garfinkle-Horowitz-Strominger, the Lyapunov and the Jacobi stability analysis gives equivalent results.

gr-qc↗
arXiv2021

Jacobi stability analysis of the classical restricted three body problem

The circular restricted three body problem, which considers the dynamics of an infinitesimal particle in the presence of the gravitational interaction with two massive bodies moving on circular orbits about their common center of mass, is a very useful model for investigating the behavior of real astronomical objects in the Solar System. In such a system, there are five Lagrangian equilibrium points, and one important characteristic of the motion is the existence of linearly stable equilibria at the two equilibrium points that form equilateral triangles with the primaries, in the plane of the primaries' orbit. We analyze the stability of motion in the restricted three body problem by using the concept of Jacobi stability, as introduced and developed in the Kosambi-Cartan-Chern (KCC) theory. The KCC theory is a differential geometric approach to the variational equations describing the deviation of the whole trajectory of a dynamical system with respect to the nearby ones. We obtain the general result that, from the point of view of the KCC theory and of Jacobi stability, all five Lagrangian equilibrium points of the restricted three body problem are unstable.

astro-ph.IM↗
arXiv2018

Phase-plane analysis of the timelike geodesics around a spherically symmetric static dilaton black hole

In this note we take a dynamical systems approach to the equations of motion of a free test particle moving around a spherically symmetric static dilaton black hole, written in the Einstein frame. The equations of motion are obtained using the Euler-Lagrange formalism. Using the first integrals of motion, we reach the conclusion that the free test particles are moving in a plane, named \emph{plane of motion}. In it we analyze the existence and nature of the equilibrium points and compare the behavior of free test particles near the equilibrium points using the dynamics systems approach. The study revealed that in the exact phase-plane exist distinct regions of motion, separated through a curve named \emph{separatrix}. In the end we obtained a relation between the parameters describing the black hole and the free test particle that holds on a parabolic separatrix.

gr-qc↗
arXiv2016

Circular orbits, Lyapunov stability and Manev-type forces

In this article we study the stability in the sense of Lyapunov of the circular orbits in the generalized Manev two bodies problem. First, we explore the existence of the circular orbits and determine their radius. Then, using the first integrals of motion we build a positive definite function, known as a Lyapunov function. It's existence proves that the circular orbit is stable in the sense of Lyapunov. In the end, we consider several real systems of two bodies and compare the characteristics of the circular orbits in Newtonian and modified Manev gravitational field, arguing about our possibilities to observe the differences between the motion in these two fields.

gr-qc↗
arXiv2015

Stability in sense of Lyapunov of circular orbits in Manev potential

In this article we consider the motion of two bodies under the action of a Manev central force. We obtain the radius of the circular orbit and analyze its stability in sense of Lyapunov. Drawn on the first integrals of angular momentum and energy, we build a positive definite function which satisfies the Lyapunov's theorem of stability. The existence of the Lyapunov function prove that the circular orbits in Manev two body problem are stable at any perturbation. In the end we compare these results with those valid for the circular orbits in the Newtonian gravitational field.

gr-qc↗
arXiv2015

Timelike geodesics around a charged spherically symmetric dilaton black hole

In this paper we study the timelike geodesics around a spherically symmetric charged dilaton black hole. The trajectories around the black hole are classified using the effective potential of a free test particle. This qualitative approach enables us to determine the type of the orbit described by the test particle without solving the equations of motion, if the parameters of the black hole and the particle are known. The connections between these parameters and the type of orbit described by the particle are obtained. To visualize the orbits we solve numerically the equation of motions for different values of the parameters envolved in our analysis. The effective potential of a free test particle looks different for a non-extremal and an extremal black hole, therefore we have examined separately these two types of black holes.

gr-qc↗
arXiv2012

Inverse problem, precessing orbits and autonomous forces

In the framework of the inverse problem of Dynamics we investigate the compatibility between a two-parametric family of precessing orbits and autonomous force fields. In a previous work, for a specific choice of the two parameters in the precessing family of orbits, we obtained that if the family is compatible with a central force, than this is derived from a Manev's type potential. In this work we consider another choice of the parameters in the two-parametric family of precessing orbits, for which we know that there is no central force compatible and study its compatibility with an autonomous force field.

math.DS↗