Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2015. / Made available in DSpace on 2015-05-19T04:08:47Z (GMT). No. of bitstreams: 1 333395.pdf: 9089220 bytes, checksum: 384a3d93823f2347ba29d434f24b1de1 (MD5) Previous issue date: 2015 / Neste trabalho efetuamos um estudo das soluções de equações de onda em espaços curvos. Abordamos a formulação das equações de Dirac e Klein-Gordon em uma geometria arbitrária. Como resultado, encontramos uma solução analítica para equação de Klein-Gordon no espaço tempo de uma corda cósmica. Na sequência resolvemos a equação de Dirac em 1+1 dimensões em um referencial acelerado para duas situações de interesse. Na primeira solução obtida, resolvemos a equação sem potencial escalar e obtemos soluções que representam energia discreta. No segundo caso, resolvemos para o potencial do tipo exponencial. Um resultado interessante foi a ocorrência de estados de energia nula em ambas soluções. Por fim estudamos a equação de Dirac no espaço- tempo de Melvin. Neste problema consideramos a métrica de um espaço que possui um campo magnético constante em uma direção.<br> / Abstract : In this work, we presents solutions for the wave equations in curved space-time. We use general relativity principles to formulate quantum wave equations for bosons and fermions. We find an exact solution of the Klein-Gordon equation and determine the energy spectrum of the particle in the cosmic string space-time. In addition, we obtain two exact solutions for the 1+1 dimensional Dirac equation in Rindler space-time. In the last chapter, we consider the Dirac equation in Melvin space-time. The energy spectra are computed and we show their dependence on the magnetic field.

It is known that there are nonlinear wave equations with localized solitary wave solutions. Some of these solitary waves are stable (with respect to a small perturbation of initial data)and have nonzero spin (nonzero intrinsic angular momentum in the centre of momentum frame). In this paper we consider vector-valued solitary wave solutions to a nonlinear Klein-Gordon equation and investigate the behavior of these spinning solitary waves under the in&#64258;uence of an externally imposed uniform magnetic &#64257;eld. We &#64257;nd that the only stationary spinning solitary wave solutions have spin parallel or antiparallel to the magnetic &#64257;eld direction.

Some eigenvalue inequalities for Klein-Gordon operators and fractional Laplacians restricted to a bounded domain are proved. Such operators became very popular recently as they arise in many problems ranging from mathematical finance to crystal dislocations, especially relativistic quantum mechanics and symmetric stable stochastic processes. Many of the results obtained here are concerned with finding bounds for some functions of the spectrum of these operators. The subject, which is well developed for the Laplacian, is examined from the spectral theory perspective through some of the tools used to prove analogous results for the Laplacian. This work highlights some important results, sparking interest in constructing a similar theory for Klein-Gordon operators. For instance, the Weyl asymptotics and semiclassical bounds for the Klein-Gordon operator are developed. As a result, a Berezin-Li-Yau type inequality is derived and an improvement of the bound is proved in a separate chapter. Other results involving some universal bounds for the Klein-Gordon Hamiltonian with an external interaction are also obtained.

Darmstadt, Techn. Hochsch., Habil.-Schr., 1995. / Includes bibliographical references (p. [199]-210.

Viele Problemstellungen der Naturwissenschaften führen zur Betrachtung von nichtlinearen Wellengleichungen. Dabei ist von großem Interesse, ob zu vorgegebenen kleinen Daten Lösungen eindeutig existieren und ob diese stetig von den Daten abhängen. Hilfsmittel für diese Probleme sind Aussagen über lineare Wellengleichungen. In der vorliegenden Arbeit werden lineare Klein-Gordon Gleichungen, also Wellengleichungen mit Potentialterm, mit zeitabhängiger Masse bzgl. des Verhaltens ihrer Lösungen untersucht. Von speziellem Interesse sind Resultate mit Bezug auf verallgemeinerte Energieerhaltung und sogenannte Lp – Lq decay-Abschätzungen. Aus der Arbeit geht hervor, dass man eine Klassifizierung für Gleichungen mit fallendem Masseterm finden kann. Für Gleichungen vom Wellentyp ist der Einfluss des Potentialterms gering und die Lösungen verhalten sich wie Lösungen der Wellengleichung. Dem gegenüber stehen Gleichungen vom Klein-Gordon-Typ mit erkennbarem Einfluss des Masseterms. Ausgangspunkt für die Klassifizierung ist das kritische Verhalten der Lösungen einer skaleninvarianten Gleichung mit speziellem Masseterm.

Lee Joy Yan Agatha. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves [112]-114). / Text in English; abstracts in English and Chinese. / Lee Joy Yan Agatha. / Abstract --- p.ii / Acknowledgement --- p.iii / Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xii / Chapter Chapter 1. --- Introduction --- p.1 / Chapter Chapter 2. --- The Transfer Integral Equation Method --- p.3 / Chapter 2.1 --- The System --- p.3 / Chapter 2.1.1 --- The Hamiltonian --- p.4 / Chapter 2.1.2 --- The length parameter --- p.5 / Chapter 2.1.3 --- The temperature parameter --- p.5 / Chapter 2.2 --- The Transfer Integral Equation --- p.6 / Chapter 2.2.1 --- The partition function --- p.6 / Chapter 2.2.2 --- The transfer integral equation --- p.6 / Chapter 2.2.3 --- The pseudo-Schrodinger equation approximation --- p.7 / Chapter 2.2.4 --- Distribution function of the displacements --- p.9 / Chapter 2.3 --- The Thermodynamics --- p.10 / Chapter 2.3.1 --- Internal energy and heat capacity --- p.10 / Chapter 2.3.2 --- Displacement fluctuation --- p.12 / Chapter 2.3.3 --- Displacement correlation function --- p.12 / Chapter Chapter 3. --- The Φ4 Chain --- p.14 / Chapter 3.1 --- Soliton In The Chain --- p.15 / Chapter 3.1.1 --- Kink soliton and antikink soliton --- p.15 / Chapter 3.1.2 --- Energy of a static kink --- p.18 / Chapter 3.2 --- Low Temperature WKB Approximation for the Φ4 Chain --- p.20 / Chapter 3.2.1 --- The ground state energy ε0 and tunneling-splitting contribution --- p.20 / Chapter 3.2.2 --- First order WKB approximation of ΨRo( φ) --- p.22 / Chapter 3.2.3 --- Second order WKB wavefunction ΨRo( φ)） --- p.26 / Chapter 3.2.4 --- Third order WKB wavefunction for ΨRo( φ) --- p.27 / Chapter 3.3 --- Thermodynamics --- p.28 / Chapter 3.3.1 --- Ground state energy ε0 and wavefunction Ψo( φ) --- p.28 / Chapter 3.3.2 --- Internal energy and heat capacity --- p.33 / Chapter 3.3.3 --- Displacement correlation function --- p.36 / Chapter Chapter 4. --- Other Nonlinear Klein-Gordon Models --- p.42 / Chapter 4.1 --- The φ8 Chain --- p.42 / Chapter 4.1.1 --- The potential --- p.42 / Chapter 4.1.2 --- The ground state energy εo and wavefunction Ψo( φ) --- p.44 / Chapter 4.1.3 --- Internal energy and heat capacity --- p.49 / Chapter 4.1.4 --- Displacement correlation function cyy(n) --- p.51 / Chapter 4.2 --- The Gaussian-Double-Well Chains --- p.53 / Chapter 4.2.1 --- The potential --- p.53 / Chapter 4.2.2 --- The ground state energy εo and wavefunction ψo --- p.55 / Chapter 4.2.3 --- Internal energy and heat capacity --- p.58 / Chapter 4.2.4 --- Displacement correlation function cyy(n) --- p.59 / Chapter 4.3 --- Comparison Between Different NKG Models --- p.61 / Chapter 4.3.1 --- The potentials --- p.61 / Chapter 4.3.2 --- Ground state energy εo and wavefunction ψo(ψ) --- p.65 / Chapter 4.3.3 --- Internal energy and heat capacity --- p.68 / Chapter 4.3.4 --- Displacement fluctuation --- p.70 / Chapter 4.3.5 --- Displacement correlation function cyy(n) --- p.71 / Chapter 4.4 --- Linear Response of a NKG Chain to a Static Perturbing Field --- p.75 / Chapter 4.4.1 --- The external perturbing field --- p.75 / Chapter 4.4.2 --- The linear response --- p.75 / Chapter 4.4.3 --- Linear response of an array of weakly coupled NKG chains --- p.80 / Chapter Chapter 5. --- Quantum Corrections --- p.86 / Chapter 5.1 --- The Effective Potential --- p.86 / Chapter 5.1.1 --- The smearing parameter --- p.86 / Chapter 5.1.2 --- The effective potential --- p.88 / Chapter 5.2 --- Quantum Corrections on Thermodynamics --- p.90 / Chapter 5.2.1 --- The ground state energy εo and wavefunction ψo(ψ) --- p.90 / Chapter 5.2.2 --- The heat capacity --- p.94 / Chapter 5.2.3 --- Displacement correlation function and displacement fluctuation --- p.97 / Chapter Chapter 6. --- Conclusion --- p.103 / Appendix A. Infinite-Square-Well Basis Diagonalization --- p.105 / Appendix B. Oscillator Basis Diagonalization --- p.110 / Bibliography --- p.112

Orientador: Edmundo Capelas de Oliveira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-09-25T13:12:35Z (GMT). No. of bitstreams: 1 Gomes_Denilson_D.pdf: 2902377 bytes, checksum: 93ed340e89d6a94739429631eed2a4d4 (MD5) Previous issue date: 2002 / Resumo: Neste trabalho são apresentadas e discutidas as chamadas equações de Klein-Gordon e Dirac generalizadas, associadas ao grupo de Fantappié-de Sitter - isometrias do espaço-tempo de Robertson- Walker. A equação de Klein-Gordon generalizada é obtida a partir do operador de Casimir de segunda ordem associada ao grupo de Fantappié-de Sitter. Por sua vez, a equação de Dirac generalizada é obtida fatorando o operador de Casimir de segunda ordem num produto de dois operadores de primeira ordem. A solução destas duas equações é obtida por separação de variáveis. Também é discuta a imersão do espaço-tempo de Robertson-Walker, desprovido de matéria e radiação, num espaço pseudo-euclidiano, tanto no caso de curvatura positiva como no caso de curvatura negativa. Apresentam-se ainda, os geradores da álgebra de Lie do grupo de Fantappié-de Sitter e seus respectivos operadores diferenciais / Abstract: We consider and discuss the so-called Klein-Gordon and Dirac generalized wave equations, related to Fantappié-de Sitter group - Robertson- Walker space-time isometries. The generalized Klein-Gordon wave equation is obtained by means of the second order Casimir invariant operator related to the Fantappié-de Sitter group. The generalized Dirac wave equation is obtained by writing the second order Casimir invariant operator as the product of two first order operators. The solution oí these equations is obtained by variable separation. We also discuss the Robertson- Walker space-time, without matter and radiation, embedded in a pseudo-euclidian space in both cases: positive and negative curvatures. We present the Lie algebra generator related to the Fantappié-de Sitter group and its differential operators / Doutorado / Doutor em Matemática Aplicada

In this thesis, we will study non-linear dispersive equations. The primary focus will be on the construction of the positive-time wave operator for such equations. The positive-time wave operator problem arises in the study of the asymptotics of a partial differential equation. It is a map from a space of initial data X into itself, and is loosely defined as follows: Suppose that for a solution Ψlin to the dispersive equation with no non-linearity and initial data Ψ+ there exists a unique solution Ψ to the non-linear equation with initial data ΨO such that Ψ behaves as Ψlin as t→ ∞. Then the wave operator is the map W + that takes Ψ+/sub; to Ψ0. By its definition, W+ is injective. An important additional question is whether or not the map is also surjective. If so, then every non-linear solution emanating from X behaves, in some sense, linearly as it evolves (this is known as asymptotic completeness). Thus, there is some justification for treating these solutions as their much simpler linear counterparts. The main results presented in this thesis revolve around the construction of the wave operator(s) at critical non-linearities. We will study the #8220; semi-relativistic ” Schrëdinger equation as well as the Klein-Gordon-Schrëdinger system on R2. In both cases, we will impose fairly general quadratic non-linearities for which conservation laws cannot be relied upon. These non-linearities fall below the scaling required to employ such tools as the Strichartz estimates. We instead adapt the "first iteration method" of Jang, Li, and Zhang to our setting which depends crucially on the critical decay of the non-linear interaction of the linear evolution. To see the critical decay in our problem, careful analysis is needed to treat the regime where one has spatial and/or time resonance.

Thesis (Ph.D)--Mathematics, Georgia Institute of Technology, 2010. / Committee Chair: Harrell, Evans; Committee Member: Chow, Shui-Nee; Committee Member: Geronimo, Jeffrey; Committee Member: Kennedy, Brian; Committee Member: Loss, Michael. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Universiẗat, Diss., 1998--Halle.