京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22231号 / 理博第4545号 / 新制||理||1653(附属図書館) / 京都大学大学院理学研究科数学・数理解析専攻 / (主査)教授 池田 保, 教授 雪江 明彦, 教授 並河 良典 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23273号 / 人博第988号 / 新制||人||234(附属図書館) / 2020||人博||988(吉田南総合図書館) / 京都大学大学院人間・環境学研究科共生人間学専攻 / (主査)教授 角 大輝, 教授 上木 直昌, 准教授 木坂 正史 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

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Dans cette thèse, nous analysons les propriétés géométriques des surfaces obtenues des solutions classiques des modèles sigma bosoniques et supersymétriques en deux dimensions ayant pour espace cible des variétés grassmanniennes G(m,n). Plus particulièrement, nous considérons la métrique, les formes fondamentales et la courbure gaussienne induites par ces surfaces naturellement plongées dans l'algèbre de Lie su(n). Le premier chapitre présente des outils préliminaires pour comprendre les éléments des chapitres suivants. Nous y présentons les théories de jauge non-abéliennes et les modèles sigma grassmanniens bosoniques ainsi que supersymétriques. Nous nous intéressons aussi à la construction de surfaces dans l'algèbre de Lie su(n) à partir des solutions des modèles sigma bosoniques. Les trois prochains chapitres, formant cette thèse, présentent les contraintes devant être imposées sur les solutions de ces modèles afin d'obtenir des surfaces à courbure gaussienne constante. Ces contraintes permettent d'obtenir une classification des solutions en fonction des valeurs possibles de la courbure. Les chapitres 2 et 3 de cette thèse présentent une analyse de ces surfaces et de leurs solutions classiques pour les modèles sigma grassmanniens bosoniques. Le quatrième consiste en une analyse analogue pour une extension supersymétrique N=2 des modèles sigma bosoniques G(1,n)=CP^(n-1) incluant quelques résultats sur les modèles grassmanniens. Dans le deuxième chapitre, nous étudions les propriétés géométriques des surfaces associées aux solutions holomorphes des modèles sigma grassmanniens bosoniques. Nous donnons une classification complète de ces solutions à courbure gaussienne constante pour les modèles G(2,n) pour n=3,4,5. De plus, nous établissons deux conjectures sur les valeurs constantes possibles de la courbure gaussienne pour G(m,n). Nous donnons aussi des éléments de preuve de ces conjectures en nous appuyant sur les immersions et les coordonnées de Plücker ainsi que la séquence de Veronese. Ces résultats sont publiés dans la revue Journal of Geometry and Physics. Le troisième chapitre présente une analyse des surfaces à courbure gaussienne constante associées aux solutions non-holomorphes des modèles sigma grassmanniens bosoniques. Ce travail généralise les résultats du premier article et donne un algorithme systématique pour l'obtention de telles surfaces issues des solutions connues des modèles. Ces résultats sont publiés dans la revue Journal of Geometry and Physics. Dans le dernier chapitre, nous considérons une extension supersymétrique N=2 du modèle sigma bosonique ayant pour espace cible G(1,n)=CP^(n-1). Ce chapitre décrit la géométrie des surfaces obtenues des solutions du modèle et démontre, dans le cas holomorphe, qu'elles ont une courbure gaussienne constante si et seulement si la solution holomorphe consiste en une généralisation de la séquence de Veronese. De plus, en utilisant une version invariante de jauge du modèle en termes de projecteurs orthogonaux, nous obtenons des solutions non-holomorphes et étudions la géométrie des surfaces associées à ces nouvelles solutions. Ces résultats sont soumis dans la revue Communications in Mathematical Physics. / In this Ph. D. thesis, we analyze the geometric properties of surfaces obtained from the classical solutions of the two-dimensional bosonic and supersymmetric sigma models which has Grassmann manifolds G(m,n) as target space. In particular, we consider the metric, the fundamental forms and the gaussian curvature induced by these surfaces which naturally live in the su(n) Lie algebra. The first chapter presents some preliminary tools to understand the elements of the following chapters. We present non-abelian gauge theories and bosonic grassmannian sigma models as well as its supersymmetric counterpart. Another section presents a construction of surfaces in the Lie algebra su(n) from the solutions of the bosonic sigma models. The three last chapters contained in this thesis presents the constraints that have to be imposed on the solutions of the models in order to generate constant gaussian curvature surfaces. From these constraints, we can give a classification of the solutions depending on the possible values of the curvature. The first two papers presents an investigation of these surfaces and of their associated solutions for the bosonic grassmannian sigma models. In the third paper, we generalize our approach to a supersymmetric extension of the bosonic CP^(n-1)= G(1,n) sigma model including some results for the general Grassmann manifold G(m,n). In chapter 2, we study the geometric properties of surfaces associated to holomorphic solutions of the grassmannian sigma models. We give a complete classification of these constant curvature solutions for the particular models G(2,n) with n=3,4,5. Furthermore, we establish two conjectures on the possible values of the gaussian curvature. We also give some elements of proof for these conjectures in terms of Plücker coordinates and immersions as well as Veronese curves. These results are published in the Journal of Geometry and Physics. The third chapter presents a similar analysis as in the second chapter in the case of non-holomorphic solutions of the bosonic grassmannian sigma models. This work generalizes the results obtained in the first paper and give a systematic algorithm to obtain such surfaces from the known solutions of the models. These results are published in the Journal of Geometry and Physics. In the last chapter of this thesis, we consider a N=2 supersymmetric extension of the bosonic sigma model which has the CP^(n-1)=G(1,n) manifold as target space. This chapter presents a geometric description of the surfaces obtained from the solutions of the model and shows, in the holomorphic case, that they have constant gaussian curvature if and only if the solutions consists of a generalization of the Veronese curve. Furthermore, using a gauge invariant formulation of the model in terms of orthogonal projectors, we obtain explicit non-holomorphic solutions and study the geometry of their associated surfaces. These results are submitted to Communications in Mathematical Physics.

[ES] El objetivo principal de esta tesis es el estudio de diferentes propiedades (principalmente ergódicas) de operadores de composición y de composición ponderados actuando en espacios de funciones holomorfas definidas en un espacio de Banach de dimensión infinita. Sea X un espacio de Banach y U un subconjunto abierto. Dada una aplicación φ : U → U, la acción f 7 → Cφ ( f ) = f ◦ φ define un operador, llamado operador de composición (y a φ se le llama símbolo del operador). Consideramos este operador actuando en diferentes espacios de funciones. La filosofía general es intentar caracterizar en cada caso las propiedades de nuestro interés en función de condiciones en φ. También, dada ψ: U → C, el operador de multiplicación se define como Mψ( f ) = ψ · f y (con φ como antes), el operador de composición ponderado como Cψ,φ ( f ) = ψ·( f ◦φ) (en este caso ψ se conoce como el peso o multiplicador del operador). Nuevamente, la idea es describir propiedades de estos operadores en términos de condiciones sobre φ y/o ψ. Claramente Cψ,φ = Mψ ◦ Cφ , y tomando φ = idU (la identidad en U) o ψ ≡ 1 (la función constante 1) recuperamos Mψ y Cφ . Denotamos con B a la bola unidad abierta de X . El espacio de funciones holomorfas f : B → C se denota H(B). Escribimos Hb(B) para el espacio de funciones holomorfas en B de tipo acotado y H∞(B) para el espacio de funciones holomorfas y acotadas en B. Vamos a considerar operadores de composición y de composición ponderados definidos en cada uno de estos espacios (tomando entonces U = B en la definición). También consideramos operadores de composición definidos en el espacio vectorial de polinomios continuos y m-homogéneos (denotado P (m X )). En este caso tomamos U = X . La tesis consta de cinco capítulos. En el Capítulo 1 damos las definiciones y resultados básicos necesarios para que el texto sea autocontenido. En el Capítulo 2 tratamos con operadores de composición ergódicos en media y acotados en potencias definidos en P (m X ). En el Capítulo 3 estudiamos operadores de composición ergódicos en media y acotados en potencias definidos en H(B), Hb(B) y H∞(B); tratando también el caso particular en que B es la bola de un espacio de Hilbert. En el Capítulo 4 estudiamos la compacidad de operadores de composición ponderados definidos en H∞(B), así como la acotación, reflexividad, cuándo es Montel y la compacidad (débil) en Hb(B). Finalmente, en el Capítulo 5 obtenemos resultados sobre la acotación en potencias y ergodicidad en media de operadores de composición ponderados actuando en H(B), Hb(B) y H∞(B); así como sobre compacidad y ergodicidad en media del operador de multiplicación. / [CA] L’objectiu principal d’aquesta tesi és l’estudi de diferents propietats (principalment ergòdiques) d’operadors de composició i de composició ponderats actuant en espais de funcions holomorfes en un espai de Banach de dimensió infinita. Siga X un espai de Banach i U un subconjunt obert. Donada una aplicació φ : U → U, l’acció f 7 → Cφ ( f ) = f ◦ φ defineix un operador, anomenat operador de compo- sició (i φ s’anomena símbol de l’operador). Considerem aquest operador actuant en diferents espais de funcions. La filosofia general és intentar caracteritzar en cada cas les propietats del nostre interés en funció de condicions en φ. També, donada ψ: U → C, l’operador de multiplicació es defineix com a Mψ( f ) = ψ · f i (amb φ com abans), l’operador de composició ponderat com a Cψ,φ ( f ) = ψ · ( f ◦ φ) (en aquest cas ψ es coneix com el pes o multiplicador de l’operador). Novament, la idea és descriure propietats d’aquests operadors en termes de condicions sobre φ i/o ψ. Clarament Cψ,φ = Mψ ◦ Cφ , i prenent φ = idU (la identitat en U) o ψ ≡ 1 (la funció constant 1) recuperem Mψ i Cφ . Denotem per B la bola unitat oberta d’X . L’espai de funcions holomorfes f : B → C es denota H(B). Escrivim Hb(B) per a l’espai de funcions holomorfes en B de tipus fitat i H∞(B) per a l’espai de funcions holomorfes i fitades en B. Anem a considerar ope- radors de composició i de composició ponderats definits en cadascun d’aquests espais (prenent llavors U = B en la definició). També considerem operadors de composició definits en l’espai vectorial de polinomis continus i m-homogenis (denotat P (m X )). En aquest cas prenem U = X . La tesi consta de cinc capítols. En el Capítol 1 donem les definicions i resultats bàsics necessaris perquè el text siga autocontingut. En el Capítol 2 tractem amb ope- radors de composició ergòdics en mitjana i fitats en potències definits en P (m X ). En el Capítol 3 estudiem operadors de composició ergòdics en mitjana i fitats en potències definits en H(B), Hb(B) i H∞(B); tractant també el cas particular en que B és la bola d’un espai de Hilbert. En el Capítol 4 estudiem la compacitat d’operadors de composi- ció ponderats definits en H∞(B), així com també la fitació, reflexivitat, quan és Montel i la compacitat (feble) en Hb(B). Finalment, en el Capítol 5 obtenim resultats sobre la fitació en potències i ergodicitat en mitjana d’operadors de composició ponderats actuant en H(B), Hb(B) i H∞(B); així com també sobre compacitat i ergodicitat en mitjana de l’operador de multiplicació. / [EN] The main aim in this thesis is to study different properties (mostly ergodic) of compo- sition and weighted composition operators acting on spaces of holomorphic functions defined on an infinite dimensional complex Banach space. Let X be a Banach space and U some open subset. Given a mapping φ : U → U the action f 7 → Cφ ( f ) = f ◦ φ defines an operator, called composition operator (and φ is called the symbol of the operator). We consider this operator acting on different spaces of functions. The general philosophy is to try to characterise in each case the properties of our interest in terms of conditions on φ. Also, given ψ: U → C the multiplication operator is defined as Mψ( f ) = ψ· f and (with φ as above), the weighted composition operator as Cψ,φ ( f ) = ψ · ( f ◦ φ) (here ψ is called the weight or multiplier of the operator). Again, the idea is to describe properties of these operators in terms of conditions on ψ and/or φ. Clearly Cψ,φ = Mψ ◦ Cφ , and taking φ = idU (the identity on U) or ψ ≡ 1 (the constant function 1) we recover Mψ and Cφ . We denote the open unit ball of X by B. The space of all holomorphic functions f : B → C is denoted by H(B). We write Hb(B) for the space holomorphic functions of bounded type on B, and H∞(B) for the space of bounded holomorphic functions on B. We are going to consider composition and weighted composition operators defined on each one of these spaces (taking then U = B in the definition). We also consider composition operators defined on the vector space of all continuous m-homogeneous polynomials on X (which is denoted by P (m X )). In this case we take U = X . The thesis consists of 5 chapters. In Chapter 1 we introduce definitions and ba- sic results, needed to make the text self-contained. In Chapter 2 we deal with mean ergodic and power bounded composition operators defined on P (m X ). In Chapter 3 we study mean ergodic and power bounded composition operators defined on H(B), Hb(B) and H∞(B); considering also the particular case when B is the ball of a Hilbert space. In Chapter 4 we study compactness of weighted composition operators defined on H∞(B), as well as boundedness, reflexivity, being Montel and (weak) compactness on Hb(B). Finally, in Chapter 5 we obtain different results about power bounded- ness and mean ergodicity of weighted composition operators acting on H(B), Hb(B) and H∞(B), as well as about compactness and mean ergodicity of the multiplication operator. / Santacreu Ferra, D. (2022). Composition Operators on Classes of Holomorphic Functions on Banach Spaces [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/185235

The aim of this text is to give an accessible overview to some recent results concerning contact manifolds and their symplectic fillings. In particular, we work out the weakest compatibility conditions between a symplectic manifold and a contact structure on its boundary to still be able to obtain a sensible theory (Chapter II), furthermore we prove two results (Theorem A and B in Section I.4) that show how certain submanifolds inside a contact manifold obstruct the existence of a symplectic filling or influence its topology. We conclude by giving several constructions of contact manifolds that for different reasons do not admit a symplectic filling.

Neste trabalho estudaremos a geração do semigrupos por operadores elípticos em dois espaços. Em primeiro lugar estudaremos a geração de semigrupo no espaço \'L POT.2\' (\'OMEGA\') por operadores elípticos de ordem 2m com \'OMEGA\' suficientemente regular. Mais precisamente, se \'OMEGA\' é um domínio limitado com \'PARTIAL OMEGA\' de classe \'C POT. 2m,\' L (x;D) = \'SIGMA\' / [\'alpha\'] \'< ou =\' \'a IND. alpha\' (x) \'D POT. alpha\' é um operador diferencial elíptico de ordem 2m, com \'a IND. alpha\' \'PERTENCE\' \' \'C POT.j\' (\'OMEGA\'), j = max {0, [\'alpha\'] - m}, e A : D(A) \'ESTÁ CONTIDO\' EM \'L POT. 2 (\'OMEGA\') \'SETA\' \' L POT. 2 (\'OMEGA\') é o operador linear dado por D(A) = \'H POT. 2m\' (\'OMEGA\') \'H POT. m INF. 0\' (\'OMEGA\'), (Au)(x) = L (x;D)u; então -A gera um \'C IND. 0\'-semigrupo holomorfo em \'L POT.2\' (\'OMEGA\'). ). Em segundo lugar estudaremos a geração de semigrupo em \'C IND. 0\'(\'OMEGA\") = ) = {u \'PERTENCE A\' C (\'OMEGA\' \'BARRA\") : u[\'PARTIAL omega\' = 0} por operadores elípticos de ordem 2 com \'OMEGA\' satisfazendo uma propriedade geométrica. Mais precisamente, se \'OMEGA\' ESTA CONTIDO EM\' \'R POT. n\' (n \'> ou =\' 2) é um domínio limitado que satisfaz a condição de cone exterior uniforme, L é o operador Lu := - \\\\SIGMA SUP n INF. i,j = 1\' \'a IND. ij \'D IND. ij u + \'\\SIGMA SUP. n IND. j=1 \'b IND. j\' u + cu com coeficientes reais \'a IND. ij\' , \'b IND. j\' , c que satisfazem \'b IND. j \' \'PERTENCE A\' \'L POT. INFTY\' (\'OMEGA\') , j = 1, ..., n, c \'PERTENCE A \' \'L POT> INFTY\' (OMEGA), c \'> ou =\' 0, \'a IND. ij\' \'PERTECE A\' C(\' OMEGA BARRA)\' \' INTERSECCAO\' \'L POT. INFTY\' (OMEGA),e \'A IND. 0\' é parte de L em \'C IND. 0\' (\"OMEGA\'), isto é, D(\'A IND. 0\') = {u \'PERTENCE A\' \'C IND. 0\' (\'OMEGA\') \'INTERSECÇÂO\' \'W POT. 2, n INF. loc\' (\'OMEGA\') : Lu \'PERTENCE A\' \'C IND. 0\' (\'OMEGA\')\' \'A IND. 0\' u = Lu, então -\'A IND. 0\' gera um \'C IND. 0-semigrupo holomorfo limitado em \'C IND. 0\' (\'OMEGA\') / In this work we study the generation of semigroups by elliptic operators in two spaces. Firstly we study the generation of semigroup in the space \'L POT. 2\' (OMEGA) for elliptic operators of order 2m with \'OMEGA\' regular domain. More precisely, if \'OMEGA\' is a bounded domain with \\PARTIAL OMEGA\' \'IT BELONGS\' \'C POT. 2m\', L (x, D) = \\ sigma INF.ALPHA \'> or =\' 2m, \'a IND. alpha\' ( x) \'D POT alpha\' is an elliptic differential operator of order 2m, with \'a IND. alpha\' \' \'IT BELONGS\' \'C POT. j\' (OMEGA), j = max , and A : D (A) \'THIS CONTAINED\' \'L POT. 2\' (OMEGA) \'ARROW\' \'L POT. 2\' (OMEGA) is linear operator given or D(A) = \'H POT. 2m\' (OMEGA) \'INTERSECTION\' \'H POT. m INF. 0 (OMEGA) (Au) (x) = L (x,D) u then -A generates a holomorphic \'C IND. 0\'-semigroup in \'L POT. 2\'.(OMEGA). Secondly we study the generation of semigroup in \'C IND. 0\' (OMEGA) = {u \'IT BELONGS\' (c INF. O\' (OMEGA BAR) : \'u [IND. \\partial omega\' = 0} for elliptic operators of second order with \'OMEGA\' satisfying a geometric property. That is, if \'OMEGA\' \'IT BELONGS\' \'R POT. n\' (n > or = 2) is a bounded domain that satisfies the uniform exterior cone condition, L is the elliptic operator given by Lu : = - \\SIGMA SUP. n INF. i,j = 1\' \'a IND. i, j\' \'D IND. ij \' u + \\SIGMA SUP n INF. j=1\' \'b IND j D IND j\' u + cu with real coefficients \'a IND. ij, \'b IND. j\' , c satisfying \'b ind. j\' \'IT BELONGS\' \' L POT. INFTY\' (omega), j = 1, ..., n, c \'it belongs\' \'L POT. INFTY\' (OMEGA), \'c > or =\' 0, \'\'a IND. ij \'IT BELONGS\' C (OMNEGA BAR) \'INTERSECTION\' (OMEGA), and \'A IND. 0\' is part of L in \'C IND. 0\'(OMEGA), that is, D (\'A IND. 0\') = {u \'IT BELONGS\' \'C IND. 0\' (OMEGA) INTERSECTION \'W POT. 2, n IND. loc (OMEGA)} \'A IND. 0u\' = Lu, then - \'A IND. 0\' generates a bounded holomorphic \'C IND. 0\'-semigroup on \'C IND. 0\' (OMEGA)

Neste trabalho estudaremos a geração do semigrupos por operadores elípticos em dois espaços. Em primeiro lugar estudaremos a geração de semigrupo no espaço \'L POT.2\' (\'OMEGA\') por operadores elípticos de ordem 2m com \'OMEGA\' suficientemente regular. Mais precisamente, se \'OMEGA\' é um domínio limitado com \'PARTIAL OMEGA\' de classe \'C POT. 2m,\' L (x;D) = \'SIGMA\' / [\'alpha\'] \'< ou =\' \'a IND. alpha\' (x) \'D POT. alpha\' é um operador diferencial elíptico de ordem 2m, com \'a IND. alpha\' \'PERTENCE\' \' \'C POT.j\' (\'OMEGA\'), j = max {0, [\'alpha\'] - m}, e A : D(A) \'ESTÁ CONTIDO\' EM \'L POT. 2 (\'OMEGA\') \'SETA\' \' L POT. 2 (\'OMEGA\') é o operador linear dado por D(A) = \'H POT. 2m\' (\'OMEGA\') \'H POT. m INF. 0\' (\'OMEGA\'), (Au)(x) = L (x;D)u; então -A gera um \'C IND. 0\'-semigrupo holomorfo em \'L POT.2\' (\'OMEGA\'). ). Em segundo lugar estudaremos a geração de semigrupo em \'C IND. 0\'(\'OMEGA\") = ) = {u \'PERTENCE A\' C (\'OMEGA\' \'BARRA\") : u[\'PARTIAL omega\' = 0} por operadores elípticos de ordem 2 com \'OMEGA\' satisfazendo uma propriedade geométrica. Mais precisamente, se \'OMEGA\' ESTA CONTIDO EM\' \'R POT. n\' (n \'> ou =\' 2) é um domínio limitado que satisfaz a condição de cone exterior uniforme, L é o operador Lu := - \\\\SIGMA SUP n INF. i,j = 1\' \'a IND. ij \'D IND. ij u + \'\\SIGMA SUP. n IND. j=1 \'b IND. j\' u + cu com coeficientes reais \'a IND. ij\' , \'b IND. j\' , c que satisfazem \'b IND. j \' \'PERTENCE A\' \'L POT. INFTY\' (\'OMEGA\') , j = 1, ..., n, c \'PERTENCE A \' \'L POT> INFTY\' (OMEGA), c \'> ou =\' 0, \'a IND. ij\' \'PERTECE A\' C(\' OMEGA BARRA)\' \' INTERSECCAO\' \'L POT. INFTY\' (OMEGA),e \'A IND. 0\' é parte de L em \'C IND. 0\' (\"OMEGA\'), isto é, D(\'A IND. 0\') = {u \'PERTENCE A\' \'C IND. 0\' (\'OMEGA\') \'INTERSECÇÂO\' \'W POT. 2, n INF. loc\' (\'OMEGA\') : Lu \'PERTENCE A\' \'C IND. 0\' (\'OMEGA\')\' \'A IND. 0\' u = Lu, então -\'A IND. 0\' gera um \'C IND. 0-semigrupo holomorfo limitado em \'C IND. 0\' (\'OMEGA\') / In this work we study the generation of semigroups by elliptic operators in two spaces. Firstly we study the generation of semigroup in the space \'L POT. 2\' (OMEGA) for elliptic operators of order 2m with \'OMEGA\' regular domain. More precisely, if \'OMEGA\' is a bounded domain with \\PARTIAL OMEGA\' \'IT BELONGS\' \'C POT. 2m\', L (x, D) = \\ sigma INF.ALPHA \'> or =\' 2m, \'a IND. alpha\' ( x) \'D POT alpha\' is an elliptic differential operator of order 2m, with \'a IND. alpha\' \' \'IT BELONGS\' \'C POT. j\' (OMEGA), j = max , and A : D (A) \'THIS CONTAINED\' \'L POT. 2\' (OMEGA) \'ARROW\' \'L POT. 2\' (OMEGA) is linear operator given or D(A) = \'H POT. 2m\' (OMEGA) \'INTERSECTION\' \'H POT. m INF. 0 (OMEGA) (Au) (x) = L (x,D) u then -A generates a holomorphic \'C IND. 0\'-semigroup in \'L POT. 2\'.(OMEGA). Secondly we study the generation of semigroup in \'C IND. 0\' (OMEGA) = {u \'IT BELONGS\' (c INF. O\' (OMEGA BAR) : \'u [IND. \\partial omega\' = 0} for elliptic operators of second order with \'OMEGA\' satisfying a geometric property. That is, if \'OMEGA\' \'IT BELONGS\' \'R POT. n\' (n > or = 2) is a bounded domain that satisfies the uniform exterior cone condition, L is the elliptic operator given by Lu : = - \\SIGMA SUP. n INF. i,j = 1\' \'a IND. i, j\' \'D IND. ij \' u + \\SIGMA SUP n INF. j=1\' \'b IND j D IND j\' u + cu with real coefficients \'a IND. ij, \'b IND. j\' , c satisfying \'b ind. j\' \'IT BELONGS\' \' L POT. INFTY\' (omega), j = 1, ..., n, c \'it belongs\' \'L POT. INFTY\' (OMEGA), \'c > or =\' 0, \'\'a IND. ij \'IT BELONGS\' C (OMNEGA BAR) \'INTERSECTION\' (OMEGA), and \'A IND. 0\' is part of L in \'C IND. 0\'(OMEGA), that is, D (\'A IND. 0\') = {u \'IT BELONGS\' \'C IND. 0\' (OMEGA) INTERSECTION \'W POT. 2, n IND. loc (OMEGA)} \'A IND. 0u\' = Lu, then - \'A IND. 0\' generates a bounded holomorphic \'C IND. 0\'-semigroup on \'C IND. 0\' (OMEGA)

A existência de seções globais para uxos é de central importância na teoria de sistemas dinâmicos, pois uma seção global simplica o estudo da dinâmica de um uxo reduzindo-o ao estudo da dinâmica de um difeomorsmo. Apresentamos detalhadamente a construção feita Hofer, Zehnder e Wysocki (em \'\'The dynamics on a strictly convex energy surface in R4\'\') de uma seção global para o uxo Hamiltoniano restrito a um nível de energia convexo em R4 . Uma importante consequência da existência dessa seção global é que o uxo Hamiltoniano restrito a um nível de energia convexo em R4 tem 2 ou innitas órbitas periódicas. Essa construção utiliza-se da teoria de curvas pseudo-holomorfas em simplectizações de variedades de contato desenvolvida pelos mesmos autores. Os argumentos apresentados também dão uma nova prova da Conjectura de Weinstein para formas de contato tight em S3 . / The existence of global surfaces of section to ows is of central importance in the theory of dynamical systems, as a global surface of section simplies the study of the dynamics of a ow reducing it to the study of the dynamics of a dieomorphism. We present in detail the construction due to Hofer, Wysocki and Zehnder (in \'\'The dynamics on a strictly convex energy surface in R4\'\') of a global surface of section for the Hamiltonian ow restricted to a convex energy level in R4 . An important consequence of the existence of the global surface of section is that the Hamiltonian ow restricted to a convex energy level in R4 has either 2 or innitely many periodic orbits. This construction makes use of the theory of pseudo-holomorphic curves in symplectizations of contact manifolds developed by the same authors. The arguments also give a new proof of Weinstein conjecture for tight contact forms in S3 .