|
|
The mathematical theory of perturbations in cosmology
Novák, Jan ; Pravda, Vojtěch (advisor) ; Chopovsky, A. (referee) ; Scholtz, Martin (referee)
We deal with cosmological perturbation theory in my work. We investigate General Theory of Relativity in Higher Dimensions in the Chapter 1. I mention GHP-formalism and algebraical classification of spacetimes. I use spinors to show that spacetimes of dimension 4 are special. I discuss also Kundt spacetimes, which are interesting for perturbation theory of black holes. I work with perturbations of FLRW ST's in GHP formalism in Chapter 2, which we want to use in Cosmological Inflation. The final part of my thesis is connected with scalar perturbations in f(R)-cosmologies, that can be used for explaining accelerated expansion in the last 5 billion years. I investigate the Universe at the scales of 150 Mpc, where I could not use the hydrodynamical approach. Thus I work with the generalization of the Landau's mechanical approach. I need quasi-static approximation for getting the potentials Φ and Ψ, since the equations are too complicated for direct integration. I plan to use the result also for numerical simulation of motions of dwarf galaxies in these potentials. Powered by TCPDF (www.tcpdf.org)
|
|
|
Calculus of variation in Physics and Geometry
Kuchařík, Jan ; Krýsl, Svatopluk (advisor) ; Scholtz, Martin (referee)
Název práce: Variační počet ve fyzice Autor: Jan Kuchařík Katedra / Ústav: Matematický ústav UK Vedoucí bakalářské práce: RNDr. Svatopluk Krýsl, Ph.D. Abstrakt: Ve své práci shrnuji některá základní použití variačního počtu v praktických aplikacích. Odvozuju zde nezbytný matematický aparát. Zavádím pojem matematického funkcionálu a jeho extremalizaci, odvozuji Euler-Lagrangeovu rovnici a její důsledek - Beltramiho identitu; dále se věnuji odvození metody řešení izoperimetrických úloh, která zobecňuje metodu Lagrangeových multiplikátorů. Ačkoliv se v práci vyskytují řešené úlohy nejrůznějšího typu, zaměřuju se na čtyři hlavní oblasti: Fermatův princip, Hamiltonův princip nejmenší akce, isoperimetrické úlohy a hledání geodetik. Title: Variational calculus in physics Author: Jan Kuchařík Department: Supervisor: RNDr. Svatopluk Krýsl, Ph.D. Abstract: In my research work, I try to collect some basic usage of variational calculus in practical applications. I derive all the necessary mathematical tools. I explain what is a fuctional and what it means to extremalize it, I derive Euler- Lagrange equation and its corollary - Beltrami identity. I also try to derive a method for solving isoperimetric problems which generalizes the one of the Lagrange multipliers. Although there is a variety of several different...
|
|
|
Rovnice geodetiky v prostoročasech s helikální symetrií
Tomášik, Miroslav ; Scholtz, Martin (advisor) ; Žofka, Martin (referee)
In this bachelor thesis we investigate geodesics in helically symmetric spacetimes in the framework of linearized Einstein's gravity. Work is an extension of paper by Bičák, Scholtz and Bohata [2], which is under preparation. First we introduce standard numerical methods for solving systems of ordinary differential equations. Next we present helically symmetric solution of linearized Einstein's equations and numerical code solving the geodesic equation on given background. We discuss conditions of existence of helically symmetric solution and finally we present selected results obtained by numerical simulations. We give present few particular examples of geodesics, selected phase portraits obtained by the method of the Lyapunovov exponents and visualize the causal structure of helically symmetric spacetime.
|
|
|
The mathematical theory of perturbations in cosmology
Novák, Jan ; Pravda, Vojtěch (advisor) ; Scholtz, Martin (referee) ; Chopovsky, A. (referee)
We have been studying Cosmological Perturbation Theory in this thesis. There was presented the Standard General Relativity in higher dimensions. Then we used the apparatus of so called GHP formalism and this is a generalization of the well-known NP-formalism. Scalar perturbations in f(R)-cosmology in the late Universe is the final topic, which was a logical step how to proceed further and to continue in work where was shown that four-dimensional spacetimes are special. We get the potentials φ and ψ for the case of a box 150 Mpc. We used the so called mechanical approach for the case of a cosmological background. Our approach of getting these potentials is in observable Universe new. It is interesting also in the context of simulations in these, so called nonlinear theories. Powered by TCPDF (www.tcpdf.org)
|
|
|
Termodynamika černých děr. Entropie a informace.
Liška, Marek ; Acquaviva, Giovanni (advisor) ; Scholtz, Martin (referee)
The aim of the thesis is to provide a review of black hole thermodynamics and its relation with concepts of entropy and physical information. We start by deriving the four laws of black hole thermodynamics in the context of classical general relativity. To supplement this, we use semiclassical limit of quantum mechanics to show that black holes radiate and have non-zero thermodynamic temperature. In the second part of the thesis we describe the concepts of the Shannon and von Neumann entropy and of physical information. Lastly, we discuss the use of these concepts in the context of black hole mechanics. 1
|
|
|
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...
|
|
|
Geometry of isolated horizons
Flandera, Aleš ; Scholtz, Martin (advisor)
While the formalism of isolated horizons is known for some time, only quite recently the near horizon solution of Einstein's equations has been found in the Bondi-like coordinates by Krishnan in 2012. In this framework, the space-time is regarded as the characteristic initial value problem with the initial data given on the horizon and another null hypersurface. It is not clear, however, what ini- tial data reproduce the simplest physically relevant black hole solution, namely that of Kerr-Newman which describes stationary, axisymmetric black hole with charge. Moreover, Krishnan's construction employs the non-twisting null geodesic congruence and the tetrad which is parallelly propagated along this congruence. While the existence of such tetrad can be easily established in general, its explicit form can be very difficult to find and, in fact it has not been provided for the Kerr-Newman metric. The goal of this thesis was to fill this gap and provide a full description of the Kerr-Newman metric in the framework of isolated horizons. In the theoretical part of the thesis we review the spinor and Newman-Penrose formalism, basic geometry of isolated horizons and then present our results. Thesis is complemented by several appendices.
|
|
|
Conformally related spacetimes
Knoška, Šimon ; Švarc, Robert (advisor) ; Scholtz, Martin (referee)
The main objective of this thesis is to investigate the possibility of creating Robinson-Trautman spacetimes from Kundt class of geometries. In the first chap- ter, properties of the Robinson-Trautman and Kundt geometries in arbitrary dimension are summarised. Natural coordinates adapted to the null spacetime foliation generated by non-twisting shear-free affinely parametrized null geodesic congruence are introduced. In the following chapter, general conformal trans- formation and specific conformal relation between the Robinson-Trautman and Kundt classes of spacetimes is discussed. Finally, attempts to find solutions to the field equations by employing this conformal relation in Einstein's theory of gravity as well as in 4-dimensional quadratic gravity are shown in the last chapter. 1
|
|
|
Parameterization of the Kerr solution
Miškovský, David ; Švarc, Robert (advisor) ; Scholtz, Martin (referee)
In this thesis we are exploring basic properties of the Kerr solution using se- veral coordinate systems. Later on, we are deriving general metric form of the spacetime foliated by null hypersurfaces. Employing the formalism of optical sca- lars we shall see, that geometry of a such a spacetime is non-twisting, that is it admits existence of a non-twisting affinely parametrized null geodesic congru- ence. Subsequently, we are trying to express the Kerr solution in the form of non-twisting coordinates. This form would have many applications e.g. in forma- lism of weakly isolated horizons (WHIs) for use in more realistic astrophysical models of black holes.
|
|
|
Weyl and Conformal Symmetries
Haman, Pavel ; Iorio, Alfredo (advisor) ; Scholtz, Martin (referee)
The problem whether scale invariance implies full conformal invariance, for special relativistic classical field theories, was resolved in the literature by exploiting the Weyl and diffeomorphic symmetries held simultaneously by the suitably improved corresponding theories. In a recent study it was conjectured that, for Liouville field theory, the case is different, as such theory could not have both symmetries (Weyl and diffeomorphic) at once. In this thesis we investigate that conjecture. In the first part the conformal symmetry, and the associated Witt and Virasoro algebras, are revised. Next, we review the relationship between scale and conformal invariance, using the approach of Weyl and Ricci gauging. The last part is devoted to the Liouville field theory. We prove there the incompatibility of Weyl and diffeomorphic invariance, by showing that the particular choice of the Weyl potential, necessary to have traceless energy-momentum tensor, gives rise to an action that is not a scalar under diffeomorphisms. A preliminary study of this "classical gravitational anomaly" is also performed.
|
guest ::
RSS feed.