Národní úložiště šedé literatury Nalezeno 6 záznamů.  Hledání trvalo 0.00 vteřin. 
Can extended bodies follow geodesic trajectories?
Lukes-Gerakopoulos, Georgios ; Mukherjee, Sajal
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a pole-dipole-quadrupole approximation under the Ohashi-Kyrian-Semer´ak spin supplementary condition moving in the Schwarzschild and Kerr background. Using orbital setups under which a pole-dipole body can follow geodesic motion, we explore under which conditions this can also take place in the pole-dipole-quadrupole approximation when only the mass quadrupole is taken into account. For our analysis, we employ the assumption that the dipole contribution and the quadrupole contribution vanish independentlly.
Growth of orbital resonances around a black hole surrounded by matter
Stratený, Michal ; Lukes-Gerakopoulos, Georgios
This work studies the dynamics of geodesic motion within a curved spacetime around a Schwarzschild black hole, perturbed by a gravitational field of a far axisymmetric distribution of mass enclosing the system. This spacetime can serve as a versatile model for a diverse range of astrophysical scenarios and, in particular, for extreme mass ratio inspirals as in our work. We show that the system is non-integrable by employing Poincaré surface of section and rotation numbers. By utilising the rotation numbers, the widths of resonances are calculated, which are then used in establishing the relation between the underlying perturbation parameter driving the system from integrability and the quadrupole parameter characterising the perturbed metric. This relation allows us to estimate the phase shift caused by the resonance during an inspiral.
Recurrence analysis of spinning particles in the Schwarzschild background
Zelenka, Ondřej ; Lukes-Gerakopoulos, Georgios ; Witzany, Vojtěch
In this work the dynamics of a spinning particle moving in the Schwarzschild background is studied. In particular, the methods of Poincaré section and recurrence analysis are employed to discern chaos from order. It is shown that the chaotic or regular nature of the orbital motion is reflected on the gravitational waves.
Probing dark energy through perfect fluid thermodynamics
Lukes-Gerakopoulos, Georgios ; Acquaviva, G. ; Markakis, K.
We demonstrate that the thermodynamics of a perfect fluid describing baryonic matter can, in certain limits, lead to an equation of state similar to that of dark energy. We keep the cosmic fluid equation of state quite general by just demanding that the speed of sound is positive and less than the speed of light. In this framework, we discuss some propositions by looking at the asymptotic behaviour of the cosmic fluid.
Dynamical analysis approaches in spatially curved FRW spacetimes
Kerachian, M. ; Acquaviva, G. ; Lukes-Gerakopoulos, Georgios
We summarize two agnostic approaches in the framework of spatially curved Friedmann-Robertson-Walker (FRW) cosmologies discussed in detail in (Kerachian et al., 2020, 2019). The first case concerns the dynamics of a fluid with an unspecified barotropic equation of state (EoS), for which the only assumption made is the non-negativity of the fluid’s energy density. The second case concerns the dynamics of a non-minimally coupled real scalar field with unspecified positive potential. For each of these models, we define a new set of dimensionless variables and a new evolution parameter. In the framework of these agnostic setups, we are able to identify several general features, like symmetries, invariant subsetsand critical points, and provide their cosmological interpretation.
Chaotic motion in the Johannsen-Psaltis spacetime
Zelenka, Ondřej ; Lukes-Gerakopoulos, Georgios
The Johannsen-Psaltis spacetime is a perturbation of the Kerr spacetime designed to avoid pathologies like naked singularities and closed timelike curves. This spacetime depends not only on the mass and the spin of the compact object, but also on extra parameters, making the spacetime deviate from Kerr. In this work we consider only the lowest order physically meaningful extra parameter. We use numerical examples to show that geodesic motion in this spacetime can exhibit chaotic behavior. We study the corresponding phase space by using Poincaré sections and rotation numbers to show chaotic behavior, and we use Lyapunov exponents to directly estimate the sensitivity to initial conditions for chaotic orbits.

Chcete být upozorněni, pokud se objeví nové záznamy odpovídající tomuto dotazu?
Přihlásit se k odběru RSS.