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Gravitační vlny v expandujících vesmírech
Pavičevič, Mak ; Bičák, Jiří (advisor) ; Kofroň, David (referee)
in English In the present work we are analysing the asymptotic behaviour of vacuum spacetimes describing gravitational waves in universes with anisotropic expansion. The thesis is divided into two main parts. In the first chapter we review cylindrical gravitational waves and their cosmological generalizations; Bondi-Sachs formalism, Penrose's null infinity and the peeling property of the Riemann tensor are summarized. Symmetry reduction, a (2+1)-dimensional formalism, is presented in detail and used in calculations. Generalization of the symmetry reduction to other dimensions and relation to Brans-Dicke theory is carried out. In the second chapter we analyse solutions describing cosmological gravitational waves proposed in the literature and discuss their relation to boost-rotation symmetric spacetimes. After utilizing the symmetry reduction, Kasner and Bianchi VI models are chosen as background solutions. The behaviour of the metric is encoded in a single function, a solution to the linear wave equation. The full solution is then a superposition of the gravitational wave representing, for example, pulses, and the background one. We calculate the Riemann and the Cotton tensor components of the 3-spacetimes and discuss the conformal completion. A comparison with four-dimensional behaviour is also...
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Matter Models in General Relativity with a Decreasing Number of Symmetries
Gürlebeck, Norman ; Bičák, Jiří (advisor) ; Fraundiener, Jörg (referee) ; Ledvinka, Tomáš (referee)
Title: Matter Models in General Relativity with a Decreasing Number of Sym- metries Author: Norman Gürlebeck Institute: Institute of theoretical physics Supervisor: Prof. RNDr. Jiří Bičák, DrSc., dr.h.c. Abstract: We investigate matter models with different symmetries in general relativity. Among these are thin (massive and massless) shells endowed with charge or dipole densities, dust distributions and rotating perfect fluid solutions. The electromagnetic sources we study are gravitating spherical symmetric condensers (including the implications of the energy conditions) and arbitrary gravitating shells endowed with a general test dipole distribution. For the latter the Israel formalism is extended to cover also general discontinuous tangential components of the electromagnetic test field, i.e., surface dipole densities. The formalism is applied to two examples and used to prove some general properties of dipole distributions. This is followed by a discussion of axially symmetric, stationary rigidly rotating dust with non-vanishing proper volume. The metric in the interior of such a configuration can be determined completely in terms of the mass density along the axis of rotation. The last matter models we consider are non-axially symmetric, stationary and rotating perfect fluid solutions. This is done with a...
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Electromagnetic Waves in Dispersiveand Refractive Relativistic Systems
Bezděková, Barbora ; Bičák, Jiří (advisor) ; Heyrovský, David (referee)
Study of light rays (light world lines) plays a significant role in many of astro- physical applications. Light rays are mainly studied in terms of so-called grav- itational lensing. However, the majority of studies are mainly focused on light propagation in vacuum. If the refractive and dispersive medium characterised by refractive index n is considered, effects occurring due to the medium presence need to be taken into account, which significantly complicates the problem. In the present thesis, rays propagating through simple refractive and dispersive systems, such as plane differentially sheared medium, are studied. In order to simplify the problem, the Hamiltonian equations of motion are used. The ray trajectories in the vicinity of Kerr black hole as well as accessible regions for the rays are also studied. Radial variation of the medium velocity is considered. Due to the recent increase of publications focused on the gravitational lensing in plasma, a detailed review summarizing the results obtained recently is included. 1
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Radiation problems of relativistic systems with symmetries
Bohata, Martin ; Bičák, Jiří (advisor) ; Ledvinka, Tomáš (referee)
The thesis deals with system of interacting particles producing eld with helical symmetry within linear theories of scalar and electromagnetic elds in Minkowski spacetime. Advanced and retarded elds are found of a particle on a circular orbit in space - thus moving along a helical trajectory in spacetime. The results are used in a dynamic (self-consistent) two-body problem under the assumption that the interaction between the particles is mediated by both retarded and advanced elds. As a consequence no radiation reaction force arise and the helical symmetry is maintained. The two-body problem of scalar and electromagnetic elds is discussed in a noninertial system in which particles are at rest. In both cases equilibrium conditions are found and the existence and uniqueness of solution is proved. The equilibrium radius is found explicitly in case of two-body electromagnetic problem in an aproximation of small velocities. In the next part the problem is generalized to the case of N particles producing electromagnetic eld with helical symmetry. The existence of equilibrium conguration is proved in general, and the uniqueness is shown in the aproximation of small velocities.
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Model Problems of the Theory of Gravitation
Pilc, Marián ; Bičák, Jiří (advisor) ; Langer, Jiří (referee) ; Balek, Vladimír (referee)
Title: Model Problems of the Theory of Gravitation Author: Marián Pilc Department: Institute of Theoretical Physics Faculty of Mathematics and Physics Supervisor: prof. RNDr. Jiří Bičák, DrSc., dr. h. c., Institute of Theoretical Physics Faculty of Mathematics and Physics Abstract: Equations of motion for general gravitational connection and orthonormal coframe from the Einstein-Hilbert type action of the Einstein-Cartan theory are derived. Ad- ditional gauge freedom is geometrically interpreted. Our formulation does not fix coframe to be tangential to spatial section hence Lorentz group is still present as part of gauge freedom. 3+1 decomposition introduces tangent Minkowski structures hence Hamilton-Dirac approach to dynamics works with Lorentz connection over spatial sec- tion. The second class constraints are analyzed and Dirac bracket is defined.Reduction of phase space is performed and canonical coordinates are introduced. The second part of this thesis is dedicated to quantum formulation of Einstein-Cartan theory. Point version of Einstein-Cartan phase space is introduced. Basic variables, crucial for quan- tization, are derived via groups acting on the phase space and their selfadjoint represen- tation is found. Representation of basic variables of Einstein-Cartan theory is derived via infinite...
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Helical symmetry and the non-existence of asymptotically flat periodic solutions in general relativity
Scholtz, Martin ; Bičák, Jiří (advisor) ; Krtouš, Pavel (referee) ; Fraundiener, Jörg (referee)
1 Title Helical symmetry and the non-existence of asymptotically flat periodic solutions in general relativity Author Martin Scholtz Department Institute of theoretical physics Faculty of Mathematics and Physics Charles University in Prague Supervisor Prof. RNDr. Jiří Bičák, DrSc., dr. h.c. Abstract. No exact helically symmetric solution in general relativity is known today. There are reasons, however, to expect that such solutions, if they exist, cannot be asymptotically flat. In the thesis presented we investigate a more general question whether there exist periodic asymptotically flat solutions of Einstein's equations. We follow the work of Gibbons and Stewart [3] who have shown that there are no periodic vacuum asymptotically flat solutions an- alytic near null infinity I. We discuss necessary corrections of Gibbons and Stewart proof and generalize their results for the system of Einstein-Maxwell, Einstein-Klein-Gordon and Einstein-conformal-scalar field equations. Thus, we show that there are no asymptotically flat periodic space-times analytic near I if as the source of gravity we take electromagnetic, Klein-Gordon or conformally invariant scalar field. The auxilliary results consist of corresponding confor- mal field equations, the Bondi mass and the Bondi massloss formula for scalar fields. We also...
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Selected problems in relativistic cosmology
Kerachian, Morteza ; Bičák, Jiří (advisor) ; Balek, Vladimír (referee) ; Vikman, Alexander (referee)
In this work, we studied three selected problems in FRW spacetime. In the first part, we analysed the motion of a test particle in the homogeneous and isotropic universe. We presented a framework in which one can derive the uniformly accelerated trajectory and geodesic motion if a scale factor for a given spacetime is provided as a function of coordinate time. By applying the confomal time transformation, we were able to convert second order differential equations of motion in FRW spacetime to first order differential equations. From this, we managed to obtain a formalism to derive the uniformly accelerated trajectory of a test particle in spatially curved FRW spacetime. The second part of this work is devoted to dynamical cosmology. In particular, we analyse the cases of barotropic fluids and non-minimally coupled scalar field in spatially curved FRW spacetime. First, we set up the dynamical systems for an unspecified EoS of a barotropic fluid case and an unspecified positive potential for a non-minimal coupled scalar field case. For both of these systems, we determined well-defined dynamical variables valid for all curvatures. In the framework of these general setups we discovered several characteristic features of the systems, such as invariant subsets, symmetries, critical points and their...
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Conservation laws with respect to curved backgrounds associated with black holes and cosmological models
Pavičevič, Mak ; Bičák, Jiří (advisor) ; Schmidt, Josef (referee)
in English We review the problem of defining energy, momentum etc. and their con- servation in curved spacetimes and a possible resolution in the form of a background spacetime. Our focus is set on superpotentials, which, when in- tegrated on a spatial boundary, yield conserved charges, while a conserved vector current is a divergence of a superpotential. Within this thesis, we build a minimal mathematical formalism necessary to prove and interpret Noether's theorem which unites symmetries and conservation laws. We em- phasize the significance of Killing vector fields - generators of isometries. After a short historical overview, the KBL superpotential is presented in de- tail, which makes it possible to define conserved quantities with respect to a curved background spacetime. We then employ its generalization within the Horndeski scalar-tensor theory of gravity. We concentrate on a subclass con- taining non-minimal derivative coupling of the Einstein tensor and a scalar field. We find superpotentials for spherically symmetric, static spacetimes (e.g. exterior of black holes) and time-dependent cosmological spacetimes, in particular with respect to (Anti-)de Sitter backgrounds. 1
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Electromagnetic Waves in Dispersiveand Refractive Relativistic Systems
Bezděková, Barbora ; Bičák, Jiří (advisor) ; Heyrovský, David (referee)
Study of light rays (light world lines) plays a significant role in many of astro- physical applications. Light rays are mainly studied in terms of so-called grav- itational lensing. However, the majority of studies are mainly focused on light propagation in vacuum. If the refractive and dispersive medium characterised by refractive index n is considered, effects occurring due to the medium presence need to be taken into account, which significantly complicates the problem. In the present thesis, rays propagating through simple refractive and dispersive systems, such as plane differentially sheared medium, are studied. In order to simplify the problem, the Hamiltonian equations of motion are used. The ray trajectories in the vicinity of Kerr black hole as well as accessible regions for the rays are also studied. Radial variation of the medium velocity is considered. Due to the recent increase of publications focused on the gravitational lensing in plasma, a detailed review summarizing the results obtained recently is included. 1
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