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単連結べき零Lie群のパラメータ剛性をもつ作用 / Parameter rigid actions of simply connected nilpotent Lie groups丸橋, 広和 24 March 2014 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18044号 / 理博第3922号 / 新制||理||1566(附属図書館) / 30902 / 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 浅岡 正幸, 教授 加藤 毅, 教授 藤原 耕二 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
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Infinite discrete group actionsKairzhan, Adilbek January 2016 (has links)
The nature of this paper is expository. The purpose is to present the fundamental material concerning actions of infinite discrete groups on the n-sphere and pseudo-Riemannian space forms based on the works of Gehring, Martin and Kulkarni and provide appropriate examples. Actions on the n-sphere split it into ordinary and limit sets. Assuming, additionally, that a group acting on the n-sphere has a certain convergence property, this thesis includes conditions for the existence of a homeomorphism between the limit set and the set of Freudenthal ends, as well as topological and quasiconformal conjugacy between convergence and Mobius groups. Since the certain pseudo-Riemannian space forms are diffeomorphic to non-compact spaces, the work of Hambleton and Pedersen gives conditions for the extension of discrete co-compact group actions on pseudo-Riemannian space forms to actions on the sphere. An example of such an extension is described. / Thesis / Master of Science (MSc)
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Lefschetz Properties of Monomial IdealsAltafi, Nasrin January 2018 (has links)
This thesis concerns the study of the Lefschetz properties of artinian monomial algebras. An artinian algebra is said to satisfy the strong Lefschetz property if multiplication by all powers of a general linear form has maximal rank in every degree. If it holds for the first power it is said to have the weak Lefschetz property (WLP). In the first paper, we study the Lefschetz properties of monomial algebras by studying their minimal free resolutions. In particular, we give an afirmative answer to an specific case of a conjecture by Eisenbud, Huneke and Ulrich for algebras having almost linear resolutions. Since many algebras are expected to have the Lefschetz properties, studying algebras failing the Lefschetz properties is of a great interest. In the second paper, we provide sharp lower bounds for the number of generators of monomial ideals failing the WLP extending a result by Mezzetti and Miró-Roig which provides upper bounds for such ideals. In the second paper, we also study the WLP of ideals generated by forms of a certain degree invariant under an action of a cyclic group. We give a complete classication of such ideals satisfying the WLP in terms of the representation of the group generalizing a result by Mezzetti and Miró-Roig. / <p>QC 20180220</p>
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CLOSED GEODESICS ON COMPACT DEVELOPABLE ORBIFOLDSDragomir, George C. 10 1900 (has links)
<p>Existence of closed geodesics on compact manifolds was first proved by Lyusternik and Fet in the 1950s using Morse theory, and the corresponding problem for orbifolds was studied by Guruprasad and Haefliger, who proved existence of a closed geodesic of positive length in numerous cases. In this thesis, we develop an alternative approach to the problem of existence of closed geodesics on compact orbifolds by studying the geometry of group actions. We give an independent and elementary proof that recovers and extends the results of Guruprasad and Haefliger for developable orbifolds. We show that every compact orbifold of dimension 2, 3, 5 or 7 admits a closed geodesic of positive length, and we give an inductive argument that reduces the existence problem to the case of a compact developable orbifold of even dimension whose singular locus is zero-dimensional and whose orbifold fundamental group is infinite torsion and of odd exponent. Stronger results are obtained under curvature assumptions. For instance, one can show that infinite torsion groups do not act geometrically on simply connected manifolds of nonpositive or nonnegative curvature, and we apply this to prove existence of closed geodesics for compact orbifolds of nonpositive or nonnegative curvature. In the general case, the problem of existence of closed geodesics on compact orbifolds is seen to be intimately related to the group-theoretic question of finite presentability of infinite torsion groups, and we explore these and other properties of the orbifold fundamental group in the last chapter.</p> / Doctor of Philosophy (PhD)
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Study of cohomogeneity one three dimensional Einstein universe / Etudes des espaces d'Einstein tridimensionnels de cohomogénéité unHassani, Masoud 04 July 2018 (has links)
Dans cette thèse des actions conformes de cohomogénéité un sur l'univers d'Einstein tridimensionel sont classifiées. Notre stratégie est d'établir dans un premier temps quel peut être le groupe de transformations conformes impliqué, à conjugaison près. Nous décrivons aussi la topologie et la nature causale des orbites d'une telle action. / In this thesis, the conformal actions of cohomogeneity one on the three-dimensional Einstein universe are classified. Our strategy in this study is to determine the representation of the acting group in the group of conformal transformations of Einstein universe up to conjugacy. Also, we describe the topology and the causal character of the orbits induced by cohomogeneity one actions in Einstein universe.
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Rigidité et non-rigidité d'actions de groupes sur les espaces Lp non-commutatifs / Rigidity and non-rigidity of group actions on non-commutative Lp spacesOlivier, Baptiste 21 May 2013 (has links)
Nous étudions des propriétés de rigidité et des propriétés de non-rigidité forte d'actions de groupes sur des espaces Lp non-commutatifs. Récemment, des variantes de la propriété (T) de Kazhdan et de la propriété de point fixe (FH) ont été introduites, appelées respectivement propriété (TB) et propriété (FB), et énoncées en termes de représentations orthogonales sur un espace de Banach B. Nous nous intéressons au cas où B est un espace Lp non-commutatif Lp(M), associé à une algèbre de von Neumann M. Dans un premier temps, nous montrons qu'un groupe possédant la propriété (T) possède la propriété (TLp(M)) pour toute algèbre de von Neumann M. On en déduit que les groupes de rang supérieur ont la propriété (FLp(M)). Nous montrons que pour certaines algèbres, comme par exemple M=B(H), les propriétés (T) et (TLp(M) sont équivalentes. A l'opposé, nous caractérisons les groupes possédant la propriété (Tlp), et montrons que cette classe de groupes est strictement plus grande que celle avec la propriété (T). Dans un second temps, nous introduisons des variantes de la propriété (H) de Haagerup, les propriétés (HLp(M)) et l' a-FLp(M)-menabilité, définies en termes d'actions sur l'espace Lp(M). Nous décrivons les liens entre la propriété (H) et sa variante (HLp(M)) suivant l'algèbre M considérée. Nous montrons que les groupes possédant (H) sont a-FLp(M)-menables pour certaines algèbres M, comme par exemple le facteur II infini hyperfini. / We studied rigidity properties and strong non-rigidity properties for group actions on non-commutative Lp spaces. Recently, variants of Kazhdan's property (T) and fixed-point property (FH) were introduced, respectively called property (TB) and property (FB), and described in terms of orthogonal representations on a Banach space B. We are interested in the case where B is a non-commutative Lp space Lp(M), associated to a von Neumann algebra M. In a first part, we show that if a group has property (T), then it has property (TLp(M)) for any von Neumann algebra M. We deduce that higher rank groups have property (FLp(M)). We show that for some algebras, such as M=B(H), properties (T) and (TLp(M)) are equivalent. By contrast, we characterize groups with property (Tlp), and show that this class of groups is larger than the one with property (T). In a second part, we introduce variants of the Haagerup property (H), namely properties (HLp(M)) and a-FLp(M)-menability, defined in terms of actions on the space Lp(M). We describe relationships between property (H) and its variant (HLp(M)) for different algebras M. We show that groups with property (H) are a-FLp(M)-menable for some algebras M, such as the hyperfinite II infinite factor.
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Principal Parts on P^1 and Chow-groups of the classical discriminants.Maakestad, Helge January 2000 (has links)
No description available.
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Group Actions and Divisors on Tropical CurvesKutler, Max B. 01 May 2011 (has links)
Tropical geometry is algebraic geometry over the tropical semiring, or min-plus algebra. In this thesis, I discuss the basic geometry of plane tropical curves. By introducing the notion of abstract tropical curves, I am able to pass to a more abstract metric-topological setting. In this setting, I discuss divisors on tropical curves. I begin a study of $G$-invariant divisors and divisor classes.
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Ga-actions on Complex Affine ThreefoldsHedén, Isac January 2013 (has links)
This thesis consists of two papers and a summary. The papers both deal with affine algebraic complex varieties, and in particular such varieties in dimension three that have a non-trivial action of one of the one-dimensional algebraic groups Ga := (C, +) and Gm := (C*, ·). The methods used involve blowing up of subvarieties, the correspondances between Ga - and Gm - actions on an affine variety X with locally nilpotent derivations and Z-gradings respectively on O(X) and passing from a filtered algebra A to its associated graded algebra gr(A). In Paper I, we study Russell’s hypersurface X , i.e. the affine variety in the affine space A4 given by the equation x + x2y + z3 + t2 = 0. We reprove by geometric means Makar-Limanov’s result which states that X is not isomorphic to A3 – a result which was crucial to Koras-Russell’s proof of the linearization conjecture for Gm -actions on A3. Our method consist in realizing X as an open part of a blowup M −→ A3 and to show that each Ga -action on X descends to A3 . This follows from considerations of the graded algebra associated to O(X ) with respect to a certain filtration. In Paper II, we study Ga-threefolds X which have as their algebraic quotient the affine plane A2 = Sp(C[x, y]) and are a principal bundle above the punctured plane A2 := A2 \ {0}. Equivalently, we study affine Ga -varieties Pˆ that extend a principal bundle P over A2, being P together with an extra fiber over the origin in A2. First the trivial bundle is studied, and some examples of extensions are given (including smooth ones which are not isomorphic to A2 × A). The most basic among the non-trivial principal bundles over A2 is SL2 (C) −→ A2, A 1→ Ae1 where e1 denotes the first unit vector, and we show that any non-trivial bundle can be realized as a pullback of this bundle with respect to a morphism A2 −→ A2. Therefore the attention is then restricted to extensions of SL2(C) and find two families of such extensions via a study of the graded algebras associated with the coordinate rings O(Pˆ) '→ O(P ) with respect to a filtration which is defined in terms of the Ga -actions on P and Pˆ respectively.
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Principal Parts on P^1 and Chow-groups of the classical discriminants.Maakestad, Helge January 2000 (has links)
No description available.
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