In this dissertation, we generalize the work of Bender and co-workers to derive new partially-integrable hierarchies of various PT -symmetric, nonlinear partial differential equations. The possible integrable members are identified employing the Painlev´e Test, a necessary but not sufficient integrability condition, and are indexed by the integer n, corresponding to the negative of the order of the dominant pole in the singular part of the Painlev´e expansion for the solution. For the PT -symmetric Korteweg-de Vries (KdV) equation, as with some other hierarchies, the first or n = 1 equation fails the test, the n = 2 member corresponds to the regular KdV equation, while the remainder form an entirely new, possibly integrable hierarchy. Integrability properties of the n = 3 and n = 4 members, typical of partially-integrable systems, including B¨acklund Transformations, a ’near-Lax Pair’, and analytic solutions are derived. The solutions, or solitary waves, prove to be algebraic in form, and the extended homogeneous balance technique appears to be the most efficient in exposing the near-Lax Pair. The PT -symmetric Burgers’ equation fails the Painlev´e Test for its n = 2 case, but special solutions are nonetheless obtained. Also, PT -Symmetric hierarchies of 2+1 Burgers’ and Kadomtsev-Petviashvili equations, which may prove useful in applications are analyzed. Extensions of the Painlev´e Test and Invariant Painlev´e analysis to 2+1 dimensions are utilized, and BTs and special solutions are found for those cases that pass the Painlev´e Test.

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Orientador: Abraham Hirsz Zimerman / Banca: Dionisio Bazeia Filho / Banca: Cesar Rogério de Oliveira / Banca: Iberê Luiz Caldas / Banca: Antônio Lima Santos / Resumo: Esta tese aborda a conexão entre modelos integráveis e as equações de Painlevé. Começamos estendendo o método do truncamento modificado afim de encontrar transformações de Bäcklund para a hierarquia mKdV-Liouville e sua redução por auto-similaridade. Com este método, resolvemos parcialmente a conjectura de Kudryashov. Em seguida, estudamos o modelo misto AKNS-Lund-Regge estendido e mostramos que este modelo pode ser reduzido às equações PIV e PV para valores particulares dos parâmetros. Nós também construimos o modelo PIII-PV simétrico afim de unificar alguns casos da equação PIII com a equação PV. Posteriormente, buscamos os vínculos canônicos apropriados que reduzem o modelo 4-bósons ao modelo PIII-PV simétrico. Para isso, elaboramos o método do ansatz de vínculos. Complementarmente, apresentamos um método para encontrar soluções de equações diferenciais em D dimensões no adendo e aplicamos ao modelo 'lâmbda'fi'POT.4 / Abstract: This thesis studies the connection among integrable models and Painlev'e equations. We begin by extending the modified truncation approach in order to find B¨acklund transformations for the mKdV-Liouville hierarchy and its self-similarity reduction. With this method, we solve Kudryashov's conjecture partially. Then we study the extended mixed AKNS-Lund-Regge model and show this model can be reduced to PIV and PV equation for particular values of the parameters. We also construct the symmetric PIII-PV model in order to unify some cases of the PIII equation with the PV equation. After, we search for canonical constraints for reduce the 4-bose model to the symmetric PIII-PV model. For find the correct constraints, we construct the method of ansatz of constraints. In addition, we show a method for finding solutions for differential equations inD dimensions in the addendum. We also apply this method for the 'lâmbda'fi'POT.4 model / Doutor

Αποδείξεις θεωρημάτων για την τάξη των λύσεων των εξισώσεων ρητού τύπου και πολυωνυμικού τύπου με την βοήθεια της Θεωρίας NENVALINNA / -

The Painleve analysis plays an important role in investigating local structure of the solutions of differential equations, while Lie symmetries provide powerful tools in global solvability of equations. In this research, the method of Painleve analysis is applied to discrete nonlinear Schrodinger equations and to a family of second order nonlinear ordinary differential equations. Lie symmetries are studied together with the Painleve property for second order nonlinear ordinary differential equations.In the study of the local singularity of discrete nonlinear Schrodinger equations, the Painleve method shows the existence of solution blow up at finite time. It also determines the rate of blow-up. For second order nonlinear ordinary differential equations, the Painleve test is introduced and demonstrated in detail using several examples. These examples are used throughout the research. The Painleve property is shown to be significant for the integrability of a differential equation.After introducing one-parameter groups, a family of differential equations is determined for discussing solvability and for drawing more meaningful conclusions. This is the most general family of differential equations invariant under a given one-parameter group. The first part of this research is the classification of the integrals in the general solutions of differential equations obtained by quadratures. The second part is the application of Riemann surfaces and algebraic curves in the projective complex space to the integrands. The theories of Riemann surfaces and algebraic curves lead us to an effective way to understand the nature of the integral defined on a curve. Our theoretical work then concentrates on the blowing-up of algebraic curves at singular points. The calculation of the genus, which essentially determines the shape of a curve, becomes possible after a sequence of blowing-ups.The research shows that when combining both the Painleve property and Lie symmetries possessed by the differential equations studied in the thesis, the general solutions can be represented by either elementary functions or elliptic integrals.

Thesis (MFA)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Ronald Tobias. Big, Dramatic is a DVD accompanying the thesis. Includes bibliographical references (leaves 23-25).

In this thesis, we classify finite orbits of the action of the pure braid group over a certain large open subset of the SL(2,C) character variety of the Riemann sphere with five boundary components, i.e. Σ5. This problem arises in the context of classifying algebraic solutions of the Garnier system G2, that is the two variable analogue of the famous sixth Painleve equation PVI. The structure of the analytic continuation of these solutions is described in terms of the action of the pure braid group on the fundamental group of Σ5. To deal with this problem, we introduce a system of co-adjoint coordinates on a big open subset of the SL(2,C) character variety of Σ5. Our classifica- tion method is based on the definition of four restrictions of the action of the pure braid group such that they act on some of the co-adjoint coordi- nates of Σ5 as the pure braid group acts on the co-adjoint coordinates of the character variety of the Riemann sphere with four boundary components, i.e. Σ4, for which the classification of all finite orbits is known. In order to avoid redundant elements in our final list, a group of symmetries G of the large open subset is introduced and the final classification is achieved modulo the action of G. We present a final list of 54 finite orbits.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18046号 / 理博第3924号 / 新制||理||1566(附属図書館) / 30904 / 京都大学大学院理学研究科数学・数理解析専攻 / (主査)准教授 竹井 義次, 教授 岡本 久, 教授 熊谷 隆 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Our work is closely connected with the problem of splitting of separatrices (breaking of homoclinic orbits) in a singularly perturbed model describing gravity water waves on a surface of finite depth. The singularly perturbed model is a family of singularly perturbed fourth-order nonlinear ordinary differential equations, parametrized by an external parameter (in addition to the small parameter of the perturbations). It is known that in general separatrices will not survive a singular perturbation. However, it was proven by Tovbis and Pelinovsky that there is a discrete set of exceptional values of the external parameter for which separatrices do survive the perturbation. Since our family of equations can be written in the Hamiltonian form, the question is whether or not survival of separatrices implies integrability of the corresponding equation. The complete integrability of the system is examined from two viewpoints: 1) the existence of a second first integral in involution (Liouville integrability), and 2) the existence of single-valued, meromorphic solutions (complex analytic integrability). In the latter case, a singular point analysis is done using the technique given by Ablowitz, Ramani, and Segur (the ARS algorithm) to determine whether the system is of Painlevé-type (P-type), lacking movable critical points. The system is shown by the algorithm to fail to be of P-type, a strong indication of nonintegrability.