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1
Gundry, James Michael. "Newtonian twistor theory." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267894.
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In twistor theory the nonlinear graviton construction realises four-dimensional antiself- dual Einstein manifolds as Kodaira moduli spaces of rational curves in threedimensional complex manifolds. We establish a Newtonian analogue of this procedure, in which four-dimensional Newton-Cartan manifolds arise as Kodaira moduli spaces of rational curves with normal bundle O + O(2) in three-dimensional complex manifolds. The isomorphism class of the normal bundle is unstable with respect to general deformations of the complex structure, exhibiting a jump to the Gibbons- Hawking class of twistor spaces. We show how Newton-Cartan connections can be constructed on the moduli space by means of a splitting procedure augmented by an additional vector bundle on the twistor space which emerges when considering the Newtonian limit of Gibbons-Hawking manifolds. The Newtonian limit is thus established as a jumping phenomenon. Newtonian twistor theory is extended to dimensions three and five, where novel features emerge. In both cases we are able to construct Kodaira deformations of the flat models whose moduli spaces possess Galilean structures with torsion. In five dimensions we find that the canonical affine connection induced on the moduli space can possess anti-self-dual generalised Coriolis forces. We give examples of anti-self-dual Ricci-flat manifolds whose twistor spaces contain rational curves whose normal bundles suffer jumps to O(2 - k) + O(k) for arbitrarily large integers k, and we construct maps which portray these big-jumping twistor spaces as the resolutions of singular twistor spaces in canonical Gibbons-Hawking form. For k > 3 the moduli space itself is singular, arising as a variety in an ambient complex space. We explicitly construct Newtonian twistor spaces suffering similar jumps. Finally we prove several theorems relating the first-order and higher-order symmetry operators of the Schrödinger equation to tensors on Newton-Cartan backgrounds, defining a Schrödinger-Killing tensor for this purpose. We also explore the role of conformal symmetries in Newtonian twistor theory in three, four, and five dimensions.
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Bedford, James Andrew Peter. "On perturbative field theory and twistor string theory." Thesis, Queen Mary, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479158.
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Shah, Mitul Rasiklal. "Twistor theory and meromorphic geometry." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531998.
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Johnson, Mark William. "Enriched sheaf theory as a framework for stable homotopy theory /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/5775.
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O'Donald, Lewis John. "Twistor diagrams and quantum field theory." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306032.
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Pilato, Alejandro Miguel. "Elementary states, supergeometry and twistor theory." Thesis, University of Oxford, 1986. http://ora.ox.ac.uk/objects/uuid:d86c78d7-2e6e-4a5c-a37a-81d8dbf3ccd8.
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It is shown that Hp-1 (P+, 0 (-m-p)) is a Fréchet space, and its dual is Hq-1(P-, 0 (m-q)), where P+ and P- are the projectivizations of subsets of generalized twistor space (≌ ℂp-q) on which the hermitian form (of signature (p,q)) is positive and negative definite respectively, and 0(-m-p) denotes the sheaf of germs of holomorphic functions homogeneous of degree -m-p. It is then proven, for p = 2 and q = 2, that the subspace consisting of all twistor elementary states is dense in Hp-1(P+, 0(-m-p)). A supermanifold is a ringed space consisting of an underlying classical manifold and an augmented sheaf of Z2-graded algebras locally isomorphic to an exterior algebra. The subcategory of the category of ringed spaces generated by such supermanifolds is referred to as the super category. A mathematical framework suitable for describing the generalization of Yang-Mills theory to the super category is given. This includes explicit examples of supercoordinate changes, superline bundles, and superconnections. Within this framework, a definition of the full super Yang-Mills equations is given and the simplest case is studied in detail. A comprehensive account of the generalization of twistor theory to the super category is presented, and it is used in an attempt to formulate a complete description of the super Yang-Mills equations. New concepts are introduced, and several ideas which have previously appeared in the literature at the level of formal calculations are expanded and explained within a consistent framework.
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Barge, S. "Twistor theory and the K.P. equations." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301766.
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In this thesis, we discuss a geometric construction analogous to the Ward correspondence for the KP equations. We propose a Dirac operator based on the inverse scattering transform for the KP-II equation and discuss the similarities and differences to the Ward correspondence. We also consider the KP-I equation, describing a geometric construction for a certain class of solutions. We also discuss the general inverse scattering of the equation, how this is related to the KP-II equation and the problems with describing a single geometric construction that incorporates both equations. We also consider the Davey-Stewartson equations, which have a similar behaviour. We demonstrate explicitly the problems of localising the theory with generic boundary conditions. We also present a reformulation of the Dirac operator and demonstrate a duality between the Dirac operator and the first Lax operator for the DS-II equations. We then proceed to generalise the Dirac operator construction to generate other integrable systems. These include the mKP and Ishimori equations, and an extension to the KP and mKP hierarchies.
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Calvert, Guy. "Twistor theory, isomonodromy and the PainleveÌ equations." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427893.
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Singer, Michael Anthony. "A general theory of global twistor descriptions." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359974.
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Wong, Woon Kwong. "The twistor theory of the AKS systems." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294333.
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Adamo, Timothy M. "Twistor actions for gauge theory and gravity." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:9749662e-cbb3-4f6e-b81c-4ee17ba752fa.
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We first consider four-dimensional gauge theory on twistor space, taking as a case study maximally supersymmetric Yang-Mills theory. Using a twistor action functional, we show that gauge theory scattering amplitudes are naturally computed on twistor space in a manner that is much more efficient than traditional space-time Lagrangian techniques at tree-level and beyond. In particular, by rigorously studying the Feynman rules of a gauge-fixed version of the twistor action, we arrive at the MHV formalism. This provides evidence for the naturality of computing scattering amplitudes in twistor space as well as an alternative proof of the MHV formalism itself. Next, we study other gauge theory observables in twistor space including gauge invariant local operators and Wilson loops, and discuss how to compute their expectation values with the twistor action. This enables us to provide proofs for the supersymmetric correlation function / Wilson loop correspondence as well as conjectures on mixed Wilson loop - local operator correlators at the level of the loop integrand. Furthermore, the twistorial formulation of such observables is naturally algebro-geometric; this leads to novel recursion relations for computing mixed correlators by performing BCFW-like deformations of the observables in twistor space. Finally, we apply these twistor actions to gravity. Using the on-shell equivalence between Einstein and conformal gravity in de Sitter space, we argue that the twistor action for conformal gravity should encode the tree-level graviton scattering amplitudes of Einstein's theory. We prove this in terms of generating functionals, and derive the flat space MHV amplitude as well as a recursive version of the MHV amplitude with cosmological constant. We also include some discussion of super-connections and Coulomb branch regularization on twistor space.
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Metzner, Norman. "Twistor theory of higher-dimensional black holes." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:0c275046-2d6f-4860-9bb3-5d5e5048cd5a.
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The correspondence of stationary, axisymmetric, asymptotically flat space-times and bundles over a reduced twistor space has been established in four dimensions. The main impediment for an application of this correspondence to examples in higher dimensions is the lack of a higher-dimensional equivalent of the Ernst poten- tial. This thesis will propose such a generalized Ernst potential, point out where the rod structure of the space-time can be found in the twistor picture and thereby provide a procedure for generating solutions to the Einstein field equations in higher dimensions from the rod structure, other asymptotic data, and the requirement of a regular axis. Examples in five dimensions are studied and necessary tools are developed, in particular rules for the transition between different adaptations of the patching matrix and rules for the elimination of conical singularities.
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Jiang, Wen. "Aspects of Yang-Mills theory in twistor space." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:4f6bc303-e8d9-4004-ab90-56b85cd917c0.
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This thesis carries out a detailed investigation of the action for pure Yang-Mills theory which L. Mason formulated in twistor space. The rich structure of twistor space results in greater gauge freedom compared to the theory in ordinary space-time. One particular gauge choice, the CSW gauge, allows simplifications to be made at both the classical and quantum level. The equations of motion have an interesting form in the CSW gauge, which suggests a possible solution procedure. This is explored in three special cases. Explicit solutions are found in each case and connections with earlier work are examined. The equations are then reformulated in Minkowski space, in order to deal with an initial-value, rather than boundary-value, problem. An interesting form of the Yang-Mills equation is obtained, for which we propose an iteration procedure. The quantum theory is also simplified by adopting the CSW gauge. The Feynman rules are derived and are shown to reproduce the MHV diagram formalism straightforwardly, once LSZ reduction is taken into account. The three-point amplitude missing in the MHV formalism can be recovered in our theory. Finally, relations to Mansfield’s canonical transformation approach are elucidated.
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Mansourbeigi, Seyed M.-H. "Sheaf Theory as a Foundation for Heterogeneous Data Fusion." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7363.
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A major impediment to scientific progress in many fields is the inability to make sense of the huge amounts of data that have been collected via experiment or computer simulation. This dissertation provides tools to visualize, represent, and analyze the collection of sensors and data all at once in a single combinatorial geometric object. Encoding and translating heterogeneous data into common language are modeled by supporting objects. In this methodology, the behavior of the system based on the detection of noise in the system, possible failure in data exchange and recognition of the redundant or complimentary sensors are studied via some related geometric objects. Applications of the constructed methodology are described by two case studies: one from wildfire threat monitoring and the other from air traffic monitoring. Both cases are distributed (spatial and temporal) information systems. The systems deal with temporal and spatial fusion of heterogeneous data obtained from multiple sources, where the schema, availability and quality vary. The behavior of both systems is explained thoroughly in terms of the detection of the failure in the systems and the recognition of the redundant and complimentary sensors. A comparison between the methodology in this dissertation and the alternative methods is described to further verify the validity of the sheaf theory method. It is seen that the method has less computational complexity in both space and time.
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Lau, Eike Sören. "On generalised D-Shtukas." Bonn : Mathematisches Institut der Universität, 2004. http://catalog.hathitrust.org/api/volumes/oclc/62768207.html.
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Sayer, Richard Michael Paul. "Covering and sheaf theories on module categories." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285575.
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Rumbos, Irma Beatriz. "A sheaf representation for non-commutative rings /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70356.
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For any ring R (associative with 1) we associate a space X of prime torsion theories endowed with Golan's SBO-topology. A separated presheaf L(-,M) on X is then constructed for any right R-module M$ sb{ rm R}$, and a sufficient condition on M is given such that L(-,M) is actually a sheaf. The sheaf space rm E { buildrel{ rm p} over longrightarrow} X) etermined by L(-,M) represents M in the following sense: M is isomorphic to the module of continuous global sections of p. These results are applied to the right R-module R$ sb{ rm R}$ and it is seen that semiprime rings satisfy the required condition for L(-,R) to be a sheaf. Among semiprime rings two classes are singled out, fully symmetric semiprime and right noetherian semiprime rings; these two kinds of rings have the desirable property of yielding "nice" stalks for the above sheaf.
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Constantin, Carmen Maria. "Sheaf-theoretic methods in quantum mechanics and quantum information theory." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:788d9d90-8fb1-4e1d-a0fa-346ba64d228a.
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In this thesis we use the language of sheaf theory in an attempt to develop a deeper understanding of some of the fundamental differences - such as entanglement, contextuality and non-locality - which separate quantum from classical physics. We first present, based on the work of Abramsky and Brandenburger [2], how sheaves, defined over certain posets of physically meaningful contexts, give a natural setting for capturing and analysing important quantum mechanical phenomena, such as quantum non-locality and contextuality. We also describe how this setting naturally leads to a three level hierarchy of quantum contextuality: weak contextuality, logical non-locality and strong contextuality. One of the original contributions of this thesis is to use these insights in order to classify a particular class of multipartite entangled states, which we have named balanced states with functional dependencies. Almost all of these states turn out to be at least logically non-local, and a number of them even turn out to be strongly contextual. We then further extend this result by showing that in fact all n-qubit entangled states, with the exception of tensor products of single-qubit and bipartite maximally-entangled states, are logically non-local. Moreover, our proof is constructive: given any n-qubit state, we present an algorithm which produces n + 2 local observables witnessing its logical non-locality. In the second half of the thesis we use the same basic principle of sheaves defined over physically meaningful contexts, in order to present an elegant mathematical language, known under the name of the Topos Approach [62], in which many quan- tum mechanical concepts, such as states, observables, and propositions about these, can be expressed. This presentation is followed by another original contribution in which we show that the language of the Topos Approach is as least as expressive, in logical terms, as traditional quantum logic. Finally, starting from a topos-theoretic perspective, we develop the construction of contextual entropy in order to give a unified treatment of classical and quantum notions of information theoretic entropy.
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McNamara, Simon Richard. "Twistor inspired methods in perturbative field theory and fuzzy funnels." Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440454.
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Sanguinetti, Guido. "Complex geometry of dual isomonodromic systems." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275207.
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Sämann, Christian. "Aspects of twistor geometry and supersymmetric field theories within superstring theory." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979814936.
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Spence, Stephen Timothy. "Twistor diagrams for a Higgs-like description of the massive propagator." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320680.
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Mason, Lionel J. "Twistors in curved space time." Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:29de7cd1-84c9-4374-8f7d-9a402dd9e0ed.
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This thesis is concerned with an investigation of twistorial structures present in curved Lorentzian space-times. Chapter 1 introduces the basic definitions and some theorems that will be used later in the text. Chapter 2 investigates generalised connections that arise in twister theory. First the Cartan con-formal connection is studied, and some of the geometry underlying it is shown to be that used by Fefferman and Graham C133. Also a condition that a space-time is conformal to vacuum is given. Secondly the theory of the Chern connection associated to a C.R. manifold is developed in such a way as to make the calculation of the connection associated to a twistor C.R. manifold straight forward. A new proof of the Chern theorem of existence and uniqueness is given. The Chern connection of a twistor C.R. manifold is then calculated, and discussed. In particular S-dimensionai C.R. manifolds arising as twistor C.R. manifolds are characterised. Canonical structures peculiar to the twister case are discussed. Applications of C.R. manifold theory to algebraically special space-times are suggested. Chapter three analyses how various twistorial structures behave in linearised general relativity. First, deformations of the space of complex null geodesies corresponding to variations of the conformal structure of space-time are shown to be generated by hami1tonians. Those that correspond to variations in the metric satisfying the field equations are given, along with hamiltonians corresponding to different fields and field equations. Beneralisations to nonlinear equations are discussed. These ideas are applied to hypersurface twisters in linearised theory, using fiat hypersurfaces and Cech cohoeology. Expressions are obtained for the deformation of the complex structure of the spaces and their evolution. The results are generalised to non flat hypersurfaces using Dolbeault cohomolcgy. It is shown that certain canonically defined forms on the spin bundle are preferred Dolbeault representatives for derivatives of the twister cohomology classes corresponding to the linearised field. In chapter four I generalise the results of chapter three to curved space using the Chern connection. In particular twistorial formulations of the constraint equations are given, and a formula for the evolution that satisfies the the vacuum evolution equations is given in terms of an "infinity" twistor and a "time" twister. This is then discussed. In chapter five I make some comments on the interpretation of a three form on the spin bundle discovered by B.A.J. Sparling as the gravitational hami1tonian. I then use this to show that one can give an interpretation of Penrose's quasi-local angular momentum twistor in terms of the canonical formalism.
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Koster, Laura Rijkje Anne. "Form factors and correlation functions in N=4 super Yang-Mills theory from twistor space." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18057.
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Das Standardmodell der Teilchenphysik hat sich bis heute, mit Ausnahme der allgemeinen Relativitätstheorie, als erfolgreichste Theorie zur Beschreibung der Natur erwiesen. Störungstheoretische Rechnungen für bestimmte Mengen in Quantenchromodynamik (QCD) haben bisher unerreicht präzise Vorraussagen ermöglicht, die experimentell nachgewiesen wurden. Trotz dieser Erfolge gibt es Teile des Standardmodells und Energieskalen bei denen die Störungstheorie versagt und man nach Alternativen suchen muss. Vieles können wir hierbei verstehen, indem wir eine ähnliche Theorie untersuchen, die sogenannte planare N=4 Super Yang-Millstheorie in vier Dimensionen (N=4 SYM). Es existieren viele Indizien dafür, dass die Theorie exakte Lösungen zulässt. Dies lässt sich zurückführen auf die Integrabilität der Theorie, eine unendlich dimensionale Symmetriealgebra, die die Theorie stark einschränkt. Neben besagter Integrabilität besitzt diese Theorie auch andere spezielle Eigenschaften. So ist sie des am besten verstandenen Beispiels der Eich-/Gravitations Dualität durch die AdS/CFT Korrespondenz. Ausserdem sind die Streuamplituden von Gluonen auf Baumgraphenniveau in N=4 SYM die selben wie in Quantenchromodynamik. Diese Streuamplituden besitzen eine elegante Struktur und stellen sich als deutlich simpler heraus, als die dazugehörigen Feynmangraphen vermuten lassen. Tatsächlich umgehen viele der zur Berechnung von Streuamplituden entwickelten Masseschalenmethoden die Feynmangraphen, indem sie vorrübergehend manifeste Unitarität und Lokalität aufgeben und dadurch die Rechnungen stark vereinfachen. Alle diese Entwicklungen suggerieren, dass der konventionelle Formalismus der Theorie mit Hilfe der Wirkung im Minkowskiraum nicht der aufschlussreichste oder effizienteste Weg ist, die Theorie zu untersuchen. Diese Arbeit untersucht der Hypothese, ob dass stattdessen Twistorvariablen besser geeignet sind, die Theorie zu beschreiben. Der Twistorformalismus wurde zuerst von Roger Penrose eingeführt. Auf dem klassischen Level ist die holomorphe Chern-Simonstheorie im Twistorraum äquivalent zur klassischen selbst-dualen Yang-Mills Lösung in der Raumzeit. Die volle Twistorwirkung, welche eine Störung um diesen klassisch integrablen Sektor ist und durch eine Eichbedingung auf die N=4 SYM Wirkung reduziert werden kann, produziert unter einer anderen Eichbedingung alle sogenannten maximalhelizitätsverletzenden
(MHV) Amplituden auf Baumgraphenniveau. Durch die Einführung eines Twistorpropagators konnten auch NkMHV Amplituden effizient beschrieben werden. In dieser Arbeit erweitern wir den Twistorformalismus um auch Größen, die sich nicht auf den Masseschalen befinden, beschreiben zu können. Wir untersuchen alle lokalen eichinvarianten zusammengesetzten Operatoren im Twistorraum und zeigen, dass sie alle Baumgraphenniveau-Formfaktoren des sogenannten MHV-Typs erzeugen. Wir erweitern diese Methode zu NMHV und öher NkMHW Level in Anlehnung an die Amplituden. Schliess lich knüpfen wir an die Integrabilität an, indem wir den ein-Schleifen Dilatationsoperator in dem skalaren Sektor der Theorie im Twistorraum berechnen.The Standard Model of particle physics has proven to be, with the exception of general relativity, the most accurate description of nature to this day. Perturbative calculations for certain quantities in Quantum Chromo Dynamics (QCD) have led to the highest precision predictions that have been experimentally verified. However, for certain sectors and energy regimes, perturbation theory breaks down and one must look for alternative methods. Much can be learned from studying a close cousin of the standard model, called planar N = 4 super Yang-Mills theory in four dimensions (N = 4 SYM), for which a lot of evidence exists that it admits exact solutions. This exact solvability is due to its quantum integrability, a hidden infinite symmetry algebra that greatly constrains the theory, which has led to a lot of progress in solving the spectral problem. Integrability aside, this non-Abelian quantum field theory is special in yet other ways. For example, it is the most well understood example of a gauge/gravity duality via the AdS/CFT correspondence. Furthermore, at tree level the scattering amplitudes in its gluon sector coincide with those of Quantum Chromo Dynamics. These scattering amplitudes exhibit a very elegant structure and are much simpler than the corresponding Feynman diagram calculation would suggest. Indeed, many on-shell methods that have been developed for computing these scattering amplitudes circumvent the tedious Feynman calculation, by giving up manifest unitarity and locality at intermediate stages of the calculation, greatly simplifying the work. All these developments suggest that the conventional way in which the theory is presented, i.e. in terms of the well- known action on Minkowski space, might not be the most revealing or in any case not the most efficient way. This thesis investigates whether instead twistor variables provide a more suitable description. The twistor formalism was first introduced by Roger Penrose. At the classical level, a holomorphic Chern-Simons theory on twistor space is equivalent to classically integrable self-dual Yang-Mills solutions in space-time. A quantum perturbation around this classically integrable sector reduces to the conventional N = 4 SYM action by imposing a partial gauge condition. This action generates all so-called maximally helicity violating (MHV) amplitudes at tree level directly, when a different gauge was chosen. By including a twistor propagator into the formalism, also higher degree NkMHV amplitudes can be described efficiently. In this thesis we extend this twistor formalism to encompass (partially) off-shell quantities. We describe all gauge-invariant local composite operators in twistor space and show that they immediately generate all tree-level form factors of the MHV type. We use the formalism to compute form factors at NMHV and higher NkMHV level in parallel to how this was done for amplitudes. Finally, we move on to integrability by computing the one-loop dilatation operator in the scalar sector of the theory in twistor space.
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Casali, Eduardo. "Worldsheet methods for perturbative quantum field theory." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/265833.
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This thesis is divided into two parts. The first part concerns the study of the ambitwistor string and the scattering equations, while the second concerns the interplay of the symmetries of the asymptotic null boundary of Minkowski space, called [scri], and scattering amplitudes. The first part begins with a review of the CHY formulas for scattering amplitudes, the scattering equations and the ambitwistor string including its pure spinor version. Next are the results of this thesis concerning these topics, they are: generalizing the ambitwistor model to higher genus surfaces; calculating the one-loop NS-NS scattering amplitudes and studying their modular and factorization properties; deriving the one-loop scattering equations and analyzing their factorization; showing that, in the case of the four graviton amplitude, the ambitwistor amplitude gives the expected kinematical prefactor; matching this amplitude to the field theory expectation in a particular kinematical regime; solving the one loop scattering equations in this kinematical regime; a conjecture for the IR behaviour of the one-loop ambitwistor integrand; computing the four graviton, two-loop amplitude using pure spinors; showing that this two-loop amplitude has the correct kinematical prefactor and factorizes as expected for a field theory amplitude; generalizing the ambitwistor string to curved backgrounds; obtaining the field equations for type II supergravity as anomaly cancellation on the worldsheet; generalizing the scattering equations for curved backgrounds. The second part begins with a review of the definition of the null asymptotic boundary of four dimensional Minkowski space, its symmetry algebra, and their relation to soft particles in the S-matrix. Next are the results of this thesis concerning these topics, they are: constructing two models consisting of maps from a worldsheet to [scri], one containing the spectrum of N=8 supergravity, and the other the spectrum of N=4 super Yang-Mills; showing how certain correlators in these theories calculate the tree-level S-matrix of N=8 sugra and N=4 sYM respectively; defining worldsheet charges which encode the action of the appropriate asymptotic symmetry algebra and showing that their Ward-identities recover the soft graviton, and soft gluon factors; defining worldsheet charges for proposed extensions of these symmetry algebras and showing that their Ward-identities give the subleading soft graviton and subleading soft gluon factors.
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Santa, Cruz Sergio d'Amorim. "Construction of hyperkähler metrics for complex adjoint orbits." Thesis, University of Warwick, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307122.
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Berkouk, Nicolas. "Persistence and Sheaves : from Theory to Applications." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX032.
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L’analyse de données topologique est un domaine de recherche récent qui vise à employer les techniques de la topologie algébrique pour concevoir des descripteurs de jeux de données. Pour être utiles en pratique, ces descripteurs doivent être calculables, et posséder une notion de métrique, afin de pouvoir exprimer leur stabilité vis à vis du bruit inhérent à toutes données réelles. La théorie de la persistance a été élaborée au début des années 2000 commeun premier cadre th éorique permettant de définir detels descripteurs - les désormais bien connus codebarres. Bien que très bien adaptée à un contexte informatique, la théorie de la persistance possède certaines limitations théoriques. Dans ce manuscript,nous établissons des liens explicites entre la théorie dérivée des faisceaux munie de la distance de convolution(d’après Kashiwara-Schapira) et la théorie de la persistance.Nous commençons par montrer un théorème d’isométrie dérivée pour les faisceaux constructibles sur R, c’est à dire, nous exprimons la distance deconvolution comme une distance d’appariement entreles code-barres gradués de ces faisceaux. Cela nous permet de conclure dans ce cadre que la distance de convolution est fermée, ainsi que la classe des faisceaux constructibles sur R munie de la distance de convolution forme un espace topologique localement connexe par arcs. Nous observons ensuite que la collection desmodules de persistance zig-zag associée à une fonction à valeurs réelle possède une structure supplémentaire, que nous appelons systèmes de Mayer-Vietoris. Sous des hypothèses de finitude, nous classifions tous les systèmes de Mayer-Vietoris. Cela nous permet d’établir une correspondence fonctorielle et isométrique entre la catégorie dérivée des faisceaux constructibles sur R équipée de la distance de convolution, et la catégorie des systèmes de Mayer-Vietoris fortement finis munie de la distance d’entrelacement. Nous en déduisons une méthode de calcul des code-barres gradués faisceautiques à partir de programmes informatiques déjà implémentés par la communauté de la persistance. Nous terminons par donner une définition purement faisceautique de la notion de module de persistance éphémère. Nous établissons que la catégorie observable des modules de persistance (le quotient de la catégorie des modules de persistance par la sous catégorie des modules de persistance éphémères)est équivalente à la catégorie bien connue des -faisceauxTopological data analysis is a recent field of research aiming at using techniques coming from algebraic topology to define descriptors of datasets. To be useful in practice, these descriptors must be computable, and coming with a notion of metric, in order to express their stability properties with res-pect to the noise that always comes with real world data. Persistence theory was elaborated in the early 2000’s as a first theoretical setting to define such des-criptors - the now famous so-called barcodes. Howe-ver very well suited to be implemented in a compu-ter, persistence theory has certain limitations. In this manuscript, we establish explicit links between the theory of derived sheaves equipped with the convolu-tion distance (after Kashiwara-Schapira) and persis-tence theory.We start by showing a derived isometry theorem for constructible sheaves over R, that is, we express the convolution distance between two sheaves as a matching distance between their graded barcodes. This enables us to conclude in this setting that the convolution distance is closed, and that the collec-tion of constructible sheaves over R equipped with the convolution distance is locally path-connected. Then, we observe that the collection of zig-zag/level sets persistence modules associated to a real valued function carry extra structure, which we call Mayer-Vietoris systems. We classify all Mayer-Vietoris sys-tems under finiteness assumptions. This allows us to establish a functorial isometric correspondence bet-ween the derived category of constructible sheaves over R equipped with the convolution distance, and the category of strongly pfd Mayer-Vietoris systems endowed with the interleaving distance. We deduce from this result a way to compute barcodes of sheaves from already existing software.Finally, we give a purely sheaf theoretic definition of the notion of ephemeral persistence module. We prove that the observable category of persistence mo-dules (the quotient category of persistence modules by the sub-category of ephemeral ones) is equivalent to the well-known category of -sheaves
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Schürmann, Jörg. "Topology of singular spaces and constructible sheaves /." Basel [u.a.] : Birkhäuser, 2003. http://www.loc.gov/catdir/toc/fy0803/2003062963.html.
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Jeftha, Lindsey Craig. "A topological framework for modeling belief revision." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5353.
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Thesis (PhD (Mathematics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Classical formulations model belief revision as a deterministic process. Under certain circumstances, the process may have more than one outcome, which suggests that belief revision is non-deterministic instead. Representations exist that model belief revision in either format, and for both formats there are axiom schemes that determine whether the representation is in fact a belief revision process. Although the axiom scheme for the non-deterministic case generalises that of the deterministic case, both schemes entail that all of the beliefs held by an agent are affected by new information, which is perhaps unintuitive. Rather, one may consider that belief revision should be local, with beliefs only affected if the new information is pertinent to them. We approach the problem of belief revision from the standpoint that it is local and non-deterministic, and the purpose and contribution of this dissertation is the development of a topological framework with which to model belief revision in this manner.
AFRIKAANSE OPSOMMING: Geloofshersiening word gewoonlik as ’n deterministiese proses voorgestel. Meer as een uitkoms mag bestaan vir verskeie omstandighede, wat aandui dat die proses liewer nie-deterministies van aard is. Beide die gevalle word deur aksiomaskemas gereguleer, en die aksiomas vir die nie-deterministiese geval veralgemeen dié van die deterministiese geval. Albei aksiomaskemas stipuleer, miskien onintuïtief, dat alle gelowe van ’n agent deur die nuwe informasie geaffekteer word. ’n Beter metode is dat net daardie gelowe waarvoor die nuwe informasie toepaslik is geaffekteer word. Ons benader die probleem van geloofshersiening uit die standpunt dat dit lokaal en nie-deterministies is, en die doel en bydrae van hierdie proefskrif is dus die ontwikkeling van ’n topologiese raamwerk waarmee ons geloofshersiening op hierdie manier kan voorstel.
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Barns-Graham, Alexander Edward. "Much ado about nothing : the superconformal index and Hilbert series of three dimensional N =4 vacua." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/287950.
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We study a quantum mechanical $\sigma$-model whose target space is a hyperKähler cone. As shown by Singleton, [184], such a theory has superconformal invariance under the algebra $\mathfrak{osp}(4^*|4)$. One can formally define a superconformal index that counts the short representations of the algebra. When the hyperKähler cone has a projective symplectic resolution, we define a regularised superconformal index. The index is defined as the equivariant Hirzebruch index of the Dolbeault cohomology of the resolution, hereafter referred to as the index. In many cases, the index can be explicitly calculated via localisation theorems. By limiting to zero the fugacities in the index corresponding to an isometry, one forms the index of the submanifold of the target space invariant under that isometry. There is a limit of the fugacities that gives the Hilbert series of the target space, and often there is another limit of the parameters that produces the Poincaré polynomial for $\mathbb C^\times$-equivariant Borel-Moore homology of the space. A natural class of hyperKähler cones are Nakajima quiver varieties. We compute the index of the $A$-type quiver varieties by making use of the fact that they are submanifolds of instanton moduli space invariant under an isometry. Every Nakajima quiver variety arises as the Higgs branch of a three dimensional $\mathcal N =4$ quiver gauge theory, or equivalently the Coulomb branch of the mirror dual theory. We show the equivalence between the descriptions of the Hilbert series of a line bundle on the ADHM quiver variety via localisation, and via Hanany's monopole formula. Finally, we study the action of the Poisson algebra of the coordinate ring on the Hilbert series of line bundles. We restrict to the case of looking at the Coulomb branch of balanced $ADE$-type quivers in a certain infinite rank limit. In this limit, the Poisson algebra is a semiclassical limit of the Yangian of $ADE$-type. The space of global sections of the line bundle is a graded representation of the Poisson algebra. We find that, as a representation, it is a tensor product of the space of holomorphic functions with a finite dimensional representation. This finite dimensional representation is a tensor product of two irreducible representations of the Yangian, defined by the choice of line bundle. We find a striking duality between the characters of these finite dimensional representations and the generating function for Poincaré polynomials.
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Aratake, Hisashi. "Sheaves of Structures, Heyting-Valued Structures, and a Generalization of Łoś's Theorem." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/265174.
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Mansfield, Shane. "The mathematical structure of non-locality and contextuality." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:394bb375-db3f-4a12-bdd8-cd1ab5809573.
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Non-locality and contextuality are key features of quantum mechanics that distinguish it from classical physics. We aim to develop a deeper, more structural understanding of these phenomena, underpinned by robust and elegant mathematical theory with a view to providing clarity and new perspectives on conceptual and foundational issues. A general framework for logical non-locality is introduced and used to prove that 'Hardy's paradox' is complete for logical non-locality in all (2,2,l) and (2,k,2) Bell scenarios, a consequence of which is that Bell states are the only entangled two-qubit states that are not logically non-local, and that Hardy non-locality can be witnessed with certainty in a tripartite quantum system. A number of developments of the unified sheaf-theoretic approach to non-locality and contextuality are considered, including the first application of cohomology as a tool for studying the phenomena: we find cohomological witnesses corresponding to many of the classic no-go results, and completely characterise contextuality for large families of Kochen-Specker-like models. A connection with the problem of the existence of perfect matchings in k-uniform hypergraphs is explored, leading to new results on the complexity of deciding contextuality. A refinement of the sheaf-theoretic approach is found that captures partial approximations to locality/non-contextuality and can allow Bell models to be constructed from models of more general kinds which are equivalent in terms of non-locality/contextuality. Progress is made on bringing recent results on the nature of the wavefunction within the scope of the logical and sheaf-theoretic methods. Computational tools are developed for quantifying contextuality and finding generalised Bell inequalities for any measurement scenario which complement the research programme. This also leads to a proof that local ontological models with `negative probabilities' generate the no-signalling polytopes for all Bell scenarios.
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Koster, Laura Rijkje Anne [Verfasser], Matthias [Gutachter] Staudacher, Lionel [Gutachter] Mason, and Valentina [Gutachter] Forini. "Form factors and correlation functions in N=4 super Yang-Mills theory from twistor space / Laura Rijkje Anne Koster ; Gutachter: Matthias Staudacher, Lionel Mason, Valentina Forini." Berlin : Humboldt-Universität zu Berlin, 2017. http://d-nb.info/1189427117/34.
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Eliasson, Jonas. "Ultrasheaves." Doctoral thesis, Uppsala : Matematiska institutionen, Univ. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3762.
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Assaf, Rabih. "Approches de topologie algébrique pour l'analyse d'images." Thesis, Reims, 2018. http://www.theses.fr/2018REIMS012/document.
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La topologie algébrique, bien que domaine abstrait des mathématiques, apporte de nouveaux concepts pour le traitement d'images. En effet, ces tâches sont complexes et restent limitées par différents facteurs tels que la nécessité d’utiliser un paramétrage, l'influence de l'arrière-plan ou la superposition d'objets. Nous proposons ici des méthodes dérivées de la topologie algébrique qui diffèrent des méthodes classiques de traitement d'images par l’intégration d’informations locales vers des échelles globales grâce à des invariants topologiques. Une première méthode de segmentation d'images a été développée en ajoutant aux caractéristiques statistiques classiques d’autres de nature topologique calculées par homologie persistante. Une autre méthode basée sur des complexes topologiques a été développée dans le but de segmenter les objets dans des images 2D et 3D. Cette méthode segmente des objets dans des images multidimensionnelles et fournit une réponse à certains problèmes habituels en restant robuste vis à vis du bruit et de la variabilité de l'arrière-plan. Son application aux images de grande taille peut se faire en utilisant des superpixels. Nous avons également montré que l'homologie relative détecte le mouvement d’objets dans une séquence d'images qui apparaissent et disparaissent du début à la fin. Enfin, nous posons les bases d’un ensemble de méthodes d'analyse d'images basé sur la théorie des faisceaux qui permet de fusionner des données locales en un ensemble cohérent. De plus, nous proposons une seconde approche qui permet de comprendre et d'interpréter la structure d’une image en utilisant les invariants fournis par la cohomologie des faisceauxAlgebraic topology, which is often appears as an abstract domain of mathematics, can bring new concepts in the execution of the image processing tasks. Indeed, these tasks might be complex and limited by different factors such as the need of prior parameters, the influence of the background, the superposition of objects. In this thesis, we propose methods derived from algebraic topology that differ from classical image processing methods by integrating local information at global scales through topological invariants. A first method of image segmentation was developed by adding topological characteristics calculated through persistent homology to classical statistical characteristics. Another method based on topological complexes built from pixels was developed with the purpose to segment objects in 2D and 3D images. This method allows to segment objects in multidimensional images but also to provide an answer to known issues in object segmentation remaining robust regarding the noise and the variability of the background. Our method can be extended to large scale images by using the superpixels concept. We also showed that the relative version of homology can be used effectively to detect the movement of objects in image sequences. This method can detect and follow objects that appear and disappear in a video sequence from the beginning to the end of the sequence. Finally, we lay the foundations of a set of methods of image analysis based on sheaf theory that allows the merging of local data into a coherent whole. Moreover, we propose a second approach that allows to understand and interpret scale analysis and localization by using the sheaves cohomology
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Meidinger, David. "Integrability in weakly coupled super Yang-Mills theory: form factors, on-shell methods and Q-operators." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19241.
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Diese Arbeit untersucht die N = 4 super-Yang-Mills-Theorie bei schwacher Kopplung, mit dem Ziel eines tieferen Verständnisses von Größen der Theorie als Zustände des integrablen Modells dass der planaren Theorie zu Grunde liegt. Wir leiten On-Shell-Diagramme für Formfaktoren des chiralen Energie-Impuls-Tensor-Multipletts aus der BCFW-Rekursion her, und untersuchen deren Eigenschaften. Dies erlaubt die Herleitung eines Graßmannschen Integrals. Für NMHV-Formfaktoren bestimmen wir die Integrationskontur. Dies erlaubt es das Integral mit einer Twistor-String-Formulierung in Beziehung zu setzen. Mit Hilfe dieser Methoden zeigen wir dass Formfaktoren des chiralen Energie-Impuls-Tensor-Multipletts und On-Shell-Funktionen mit Einfügungen beliebiger Operatoren Eigenzustände integrabler Transfermatrizen sind. Diese Identitäten verallgemeinern die Yangsche Invarianz der On-Shell-Funktionen von Amplituden. Wir zeigen weiterhin dass ein Teil der Yangschen Symmetrien erhalten bleibt. Wir erweitern unsere Untersuchung auf nichtplanare On-Shell-Funktionen und zeigen dass sie ebenfalls solche Symmetrien besitzen. Weitere Identitäten mit Transfermatrizen werden hergeleitet, und zeigen insbesondere dass Diagramme auf Zylindern als Intertwiner fungieren. Als Schritt hin zur Berechnung der Eigenzustände des integrablen Modells zu höheren Schleifenordnungen untersuchen wir Einspuroperatoren. Hier erlaubt die Quantum Spectral Curve die nichtperturbative Berechnung ihres Spektrums, liefert jedoch keine Information zu den Zustände. Die QSC kann als Q-System verstanden werden, welches durch Baxter Q-Operatoren formulierbar sein sollte. Um darauf hinzuarbeiten untersuchen wir die Q-Operatoren nichtkompakter Superspinketten und entwickeln ein effiziente Methode zur Berechnung ihrer Matrixelemente. Dies erlaubt es das gesamte Q-System durch Matrizen für jeden Anregungssektor zu realisieren, und liefert die Grundlage für perturbative Rechnungungen mit der QSC in Operatorform.This thesis investigates weakly coupled N = 4 super Yang-Mills theory, aiming at a better understanding of various quantities as states of the integrable model underlying the planar theory. We use the BCFW recursion relations to develop on-shell diagrams for form factors of the chiral stress-tensor multiplet, and investigate their properties. The diagrams allow to derive a Graßmannian integral for these form factors. We devise the contour of this integral for NMHV form factors, and use this knowledge to relate the integral to a twistor string formulation. Based on these methods, we show that both form factors of the chiral stress-tensor multiplet as well as on-shell functions with insertions of arbitrary operators are eigenstates of integrable transfer matrices. These identities can be seen as symmetries generalizing the Yangian invariance of amplitude on-shell functions. In addition, a part of these Yangian symmetries are unbroken. We furthermore consider nonplanar on-shell functions and prove that they exhibit a partial Yangian invariance. We also derive identities with transfer matrices, and show that on-shell diagrams on cylinders can be understood as intertwiners. To make progress towards the calculation of the higher loop eigenstates of the integrable model, we consider single trace operators, for which the Quantum Spectral Curve determines their spectrum non-perturbatively. This formulation however carries no information about the states. The QSC is an algebraic Q-system, for which an operatorial form in terms of Baxter Q-operators should exist. To initiate the development such a formulation we investigate the Q-operators of non-compact super spin chains and devise efficient methods to evaluate their matrix elements. This allows to obtain the entire Q-system in terms of matrices for each magnon sector. These can be used as input data for perturbative calculations using the QSC in operatorial form.
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Neyra, Norbil Leodan Cordova. "Grau de aplicações G-equivariantes entre variedades generalizadas." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/55/55135/tde-12082014-153507/.
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Neste trabalho estenderemos os resultados obtidos por Hara [34] e J. Jaworowski [38] substituindo as G-variedades por G-variedades generalizadas sobre Z. Além disso, provamos uma fórmula de comparação geral para grau de aplicações de uma variedade generalizada sobre uma esfera que são equivariantes com respeito a ações de grupos finitos, obtendo uma generalização do resultado de A. Kushkuley e Z. Balanov [40]In this work, we extend the results obtained by Y. Hara [34] and J. Jaworowski [38] by replacing the free G-manifolds by free generalized G-manifolds over Z. Moreover, we prove a general comparison formula for degrees of equivariant maps from a generalized manifold to a sphere which are equivariant with respect to finite group actions, obtaining a generalization of the result of A. Kushkuley and Z. Balanov [40]
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Silva, Junior Soares da. "Introdução à cohomologia de De Rham." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/55/55135/tde-16112017-101825/.
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Começamos definindo a cohomologia clássica de De Rham e provamos alguns resultados que nos permitem calcular tal cohomologia de algumas variedades diferenciáveis. Com o intuito de provar o Teorema de De Rham, escolhemos fazer a demonstração utilizando a noção de feixes, que se mostra como uma generalização da ideia de cohomologia. Como a cohomologia de De Rham não é a única que se pode definir numa variedade, a questão da unicidade dá origem a teoria axiomática de feixes, que nos dará uma cohomologia para cada feixe dado. Mostraremos que a partir da teoria axiomática de feixes obtemos cohomologias, além das cohomologias clássicas de De Rham, a cohomologia clássica singular e a cohomologia clássica de Cech e mostraremos que essas cohomologias obtidas a partir da noção axiomática são isomorfas as definições clássicas. Concluiremos que se nos restringirmos a apenas variedades diferenciáveis, essas cohomologias são unicamente isomorfas e este será o teorema de De Rham.We begin by defining De Rhams classical cohomology and we prove some results that allow us a calculation of the cohomology of some differentiable manifolds. In order to prove De Rhams Theorem, we chose to make a demonstration using a notion of sheaves, which is a generalization of the idea of cohomology. Since De Rhams cohomology is not a only one that can be made into a variety, the question of unicity gives rise to axiomatic theory of sheaves, which give us a cohomology for each sheaf given. We will show that from the axiomatic theory of sheaves we obtain cohomologies, besides the classical cohomologies of De Rham, a singular classical cohomology and a classical cohomology of Cech and we will show that cohomologies are obtained from the axiomatic notion are classic definitions. We will conclude that if we restrict ourselves to only differentiable manifolds, these cohomologies are uniquely isomorphic and this will be De Rhams theorem.
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Daia, Liviu. "La transformation de Fourier pour les D-modules." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10126.
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Sur c#n vu comme variete algebrique, soient f la transformation de fourier pour les d-modules, f#+ la transformation de fourier faisceautique de brylinsky-malgrange-verdier, et sol le foncteur solutions. On prouve alors que pour tout d-module 1-specialisable a l'infini m, on a un isomorphisme sol(fm) f#+sol(m). Le resultat a ete conjecture en 1988 par b. Malgrange, qui l'a prouve pour m module de type fini sur l'algebre de weyl
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Wieland, Wolfgang. "Structure chirale de la gravité quantique à boucles." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4094/document.
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La relativité générale représente la description la plus précise de l'interaction gravitationnelle. Cependant, alors que la matière est régie par les lois de la mécanique quantique, la gravitation, elle, est une théorie fondamentalement classique. A l'échelle de Planck, c'est-à-dire à des distances d'environ 10E-35 mètres, les effets quantiques et ceux de la gravitation deviennent tous deux importants. A l'heure actuelle, un langage mathématique unifié et décrivant les effets physiques à cette échelle est toujours manquant. Il existe néanmoins plusieurs théories candidates à cette description, et l'une d'entre elles, la gravité quantique à boucles, est l'objet d'étude de cette thèse.Afin de tester si une théorie candidate peur fournir une description appropriée des propriétés quantiques du champ de gravitation, elle doit présenter une certaine cohérence interne du point de vue mathématique, et aussi être en accord avec les tests expérimentaux de la relativité générale. Le but de cette thèse est de développer certains outils mathématiques qui éclairent ces conditions de consistance interne, et qui permettent d'établir un lien entre différentes formulations de la théorieGeneral relativity is the most precise theory of the gravitational interaction. It is a classical field theory. All matter, on the other hand, follows the rules of quantum theory. At the Planck scale, at about distances of the order of 10E-35 meters, both theories become equally important. Today, theoretical physics lacks a unifying language to explore what happens at this scale, but there are several candidate theories available. Loop quantum gravity is one them, and it is the main topic of this thesis. To see whether a particular proposal is a viable candidate for a quantum theory of the gravitational field it must be free of internal inconsistencies, and agree with all experimental tests of general relativity. This thesis develops mathematical tools to check these
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Huang, Pengfei. "Théorie de Hodge non-abélienne et des spécialisations." Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4029.
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La premiére partie de cette thèse est la géométrie de la théorie de Hodge non-Abélienne, en particulier l’étude des propriétés géométriques des espaces de modules.Le premier résultat principal de cette partie est la construction d’un système dynamique sur l’espace de modules des fibrés de Higgs, nous montrons que les points fixes de ce système dynamique sont exactement ceux fixés par l’action de C* sur l’espace de modules des fibrés de Higgs, c’est-àdire tous les C-VHS dans l’espace de modules. Dans le même temps, nous étudions sa première variation et son comportement asymptotique.Le deuxième résultat principal de cette partie est la preuve d’une conjecture (forme faible) par Simpson sur la stratification de l’espace de modules des fibrés plats, nous prouvons que la strata d’opérateurs est la strata fermée unique de dimension minimale en étudiant l’espace de modules des chaînes holomorphes de type donné.Le troisième résultat principal de cette partie est une généralisation de la construction par Deligne en l’espace de twistor de Hitchin dans le cas de surface de Riemann, nous construisons des sections holomorphes pour ce nouvel espace de twistor, c’est-à-dire les sections de de Rham. Nous calculons les fibrés normals de ces sections, et nous avons constaté que les sections de de Rham dans l’espace de twistor de Deligne–Hitchin ont également la propriété wight 1, donc ce sont des courbes rationnelles amples. Dans le même temps, nous montrons le théorème de type Torelli pour l’espace de twistor.La deuxième partie de cette thèse est l’étude de certaines spécialisations de la correspondance de Hodge non-Abélienne. Celui-ci comprend principalement deux chapitres, le premier est une preuve fondamentale d’une conjecture liée aux représentations de carquois proposée par Reineke en 2003, nous montrons pour les représentations de carquois de type An , il existe un système de poids tel que les représentations stables par rapport à ce système de poids sont précisément celles indécomposables. Pour la deuxième, nous construisons la correspondance de Kobayashi–Hitchin pour les fibrés de carquois sur les variétés Kähleriennes généraliséesThe first part of this thesis is the geometry of non-Abelian Hodge theory, especially the study of geometric properties of moduli spaces.The first main result of this part is the construction of a dynamical system on the moduli space of Higgs bundles, we show that fixed points of this dynamical system are exactly those fixed by the C*-action on the moduli space of Higgs bundles, that is, all C-VHS in the moduli space. At the same time, we study its first variation and asymptotic behaviour.The second main result of this part is the proof of a conjecture (weak form) by Simpson on the stratification of the moduli space of flat bundles, we prove that the oper stratum is the unique closed stratum of minimal dimension by studying the moduli space of holomorphic chains of given type.The third main result of this part is a generalization of Deligne’s construction of Hitchin twistor space in Riemann surface case, we construct holomorphic sections for this new twistor space, namely the de Rham sections. We calculate the normal bundles of these sections, and we found that de Rham sections in the Deligne–Hitchin twistor space also have wight 1 property, so they are ample rational curves. We also show the Torelli-type theorem for this new twistor space
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Sebastianutti, Marco. "Geodesic motion and Raychaudhuri equations." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18755/.
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The work presented in this thesis is devoted to the study of geodesic motion in the context of General Relativity. The motion of a single test particle is governed by the geodesic equations of the given space-time, nevertheless one can be interested in the collective behavior of a family (congruence) of test particles, whose dynamics is controlled by the Raychaudhuri equations. In this thesis, both the aspects have been considered, with great interest in the latter issue. Geometric quantities appear in these evolution equations, therefore, it goes without saying that the features of a given space-time must necessarily arise. In this way, through the study of these quantities, one is able to analyze the given space-time. In the first part of this dissertation, we study the relation between geodesic motion and gravity. In fact, the geodesic equations are a useful tool for detecting a gravitational field. While, in the second part, after the derivation of Raychaudhuri equations, we focus on their applications to cosmology. Using these equations, as we mentioned above, one can show how geometric quantities linked to the given space-time, like expansion, shear and twist parameters govern the focusing or de-focusing of geodesic congruences. Physical requirements on matter stress-energy (i.e., positivity of energy density in any frame of reference), lead to the various energy conditions, which must hold, at least in a classical context. Therefore, under these suitable conditions, the focusing of a geodesics "bundle", in the FLRW metric, bring us to the idea of an initial (big bang) singularity in the model of a homogeneous isotropic universe. The geodesic focusing theorem derived from both, the Raychaudhuri equations and the energy conditions acts as an important tool in understanding the Hawking-Penrose singularity theorems.
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Mautner, Carl Irving. "Sheaf theoretic methods in modular representation theory." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-05-943.
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This thesis concerns the use of perverse sheaves with coefficients in commutative rings and in particular, fields of positive characteristic, in the study of modular representation theory. We begin by giving a new geometric interpretation of classical connections between the representation theory of the general linear groups and symmetric groups. We then survey work, joint with D. Juteau and G. Williamson, in which we construct a class of objects, called parity sheaves. These objects share many properties with the intersection cohomology complexes in characteristic zero, including a decomposition theorem and a close relation to representation theory. The final part of this document consists of two computations of IC stalks in the nilpotent cones of sl₃and sl₄. These computations build upon our calculations in sections 3.5 and 3.6 of (31), but utilize slightly more sophisticated techniques and allow us to compute the stalks in the remaining characteristics.text
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Quigley, Callum. "Twistor inspired techniques for gauge theory amplitudes." Thesis, 2005. http://hdl.handle.net/2429/16384.
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We examine recent developments in perturbative calculations of gauge theory amplitudes.
Motivated by a twistor space analysis, Cachazo, Svrcek and Witten (CSW) formulated a
new set of rules for computing scattering amplitudes, which have now been dubbed the
CSW rules. We examine the origins of these rules, and apply them to supersymmetric and
non-supersymmetric gauge theories. We review many of the recent calculations performed
using this new prescription at both the tree and one-loop levels.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Baranovsky, Vladimir. "Moduli of sheaves on surfaces and action of the oscillator algebra /." 2000. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9965058.
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Anyaegbunam, Adaeze Christiana. "Geometric algebra via sheaf theory : a view towards symplectic geometry." Thesis, 2010. http://hdl.handle.net/2263/28971.
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Yang, Haibo. "Ro(g)-graded equivariant cohomology theory and sheaves." Thesis, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2346.
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If G is a nite group and if X is a G-space, then a Bredon RO(G)-graded equivariantcohomology theory is dened on X. Furthermore, if X is a G-manifold, thereexists a natural Čech hypercohomology theory on X. While Bredon RO(G)-gradedcohomology is important in the theoretical aspects, the Čech cohomology is indispensablewhen computing the cohomology groups. The purpose of this dissertation is toconstruct an isomorphism between these two types of cohomology theories so that theinterplay becomes deeper between the theory and concretely computing cohomologygroups of classical objects. Also, with the aid of Čech cohomology, we can naturallyextend the Bredon cohomology to the more generalized Deligne cohomology.In order to construct such isomorphism, on one hand, we give a new constructionof Bredon RO(G)-graded equivariant cohomology theory from the sheaf-theoreticviewpoint. On the other hand, with Illman's theorem of smooth G-triangulation ofa G-manifold, we extend the existence of good covers from the nonequivariant tothe equivariant case. It follows that, associated to an equivariant good cover of aG-manifold X, there is a bounded spectral sequence converging to Čech hypercohomologywhose E1 page is isomorphic to the E1 page of a Segal spectral sequence whichconverges to the Bredon RO(G)-graded equivariant cohomology. Furthermore, Thisisomorphism is compatible with the structure maps in the two spectral sequences. So there is an induced isomorphism between two limiting objects, which are exactly theČech hypercohomology and the Bredon RO(G)-graded equivariant cohomology.We also apply the above results to real varieties and obtain a quasi-isomorphismbetween two commonly used complexes of presheaves.
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Blander, Benjamin A. "Local projective model structures on simplicial presheaves /." 2003. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3088717.
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Nevins, Thomas A. "Moduli spaces of framed sheaves on ruled surfaces /." 2000. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9965126.
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Sämann, Christian [Verfasser]. "Aspects of twistor geometry and supersymmetric field theories within superstring theory / von Christian Sämann." 2006. http://d-nb.info/979814936/34.
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