Sheaf Theory 1 Introduction and Definitions
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The Calabi Complex and Killing Sheaf Cohomology
The Calabi complex and Killing sheaf cohomology Igor Khavkine Department of Mathematics, University of Trento, and TIFPA-INFN, Trento, I{38123 Povo (TN) Italy [email protected] September 26, 2014 Abstract It has recently been noticed that the degeneracies of the Poisson bra- cket of linearized gravity on constant curvature Lorentzian manifold can be described in terms of the cohomologies of a certain complex of dif- ferential operators. This complex was first introduced by Calabi and its cohomology is known to be isomorphic to that of the (locally constant) sheaf of Killing vectors. We review the structure of the Calabi complex in a novel way, with explicit calculations based on representation theory of GL(n), and also some tools for studying its cohomology in terms of of lo- cally constant sheaves. We also conjecture how these tools would adapt to linearized gravity on other backgrounds and to other gauge theories. The presentation includes explicit formulas for the differential operators in the Calabi complex, arguments for its local exactness, discussion of general- ized Poincar´eduality, methods of computing the cohomology of locally constant sheaves, and example calculations of Killing sheaf cohomologies of some black hole and cosmological Lorentzian manifolds. Contents 1 Introduction2 2 The Calabi complex4 2.1 Tensor bundles and Young symmetrizers..............5 2.2 Differential operators.........................7 2.3 Formal adjoint complex....................... 11 2.4 Equations of finite type, twisted de Rham complex........ 14 3 Cohomology of locally constant sheaves 16 3.1 Locally constant sheaves....................... 16 3.2 Acyclic resolution by a differential complex............ 18 3.3 Generalized Poincar´eduality................... -
3D Holography: from Discretum to Continuum
3D Holography: from discretum to continuum Bianca Dittrich (Perimeter Institute) V. Bonzom, B. Dittrich, to appear V. Bonzom, B.Dittrich, S. Mizera, A. Riello, w.i.p. ILQGS Sep 2015 1 Overview 1.Is quantum gravity fundamentally holographic? 2.Continuum: dualities for 3D gravity. 3.Regge calculus. 4.Computing the 3D partition function in Regge calculus. One loop correction. Boundary fluctuations. 2 1 1 S = d3xpgR d2xphK −16⇡G − 8⇡G Z Z@ 1 M β M = Ar(torus) r=1 = no ↵ dependence (0.217) sol −8⇡G | −4G 1 1 S = d3xpgR d2xphK −16⇡G − 8⇡G dt Z Z@ ln det(∆ m2)= 1 d3xK(t,1 x, x)M β(0.218)M − − 0 t = Ar(torus) r=1 = no ↵ dependence (0.217) Z Z sol −8⇡G | −4G 1 K = r dt Is quantum gravity fundamentallyln det(∆ m2)= holographic?1 d3xK(t, x, x) (0.218) i↵ − − t q = e Z0 (0.219)Z • In the last years spin1 foams have made heavily use of the K = r Generalized Boundary Formulation [Oeckl 00’s +, Rovelli, et al …] Region( bdry) i↵ (0.220) • Encodes dynamicsA into amplitudes associated to (generalized)q = e space time regions. (0.219) (0.221) bdry ( ) (0.220) ARegion bdry boundary -should satisfy (the dualized) Wheeler de Witt equation Hilbert space -gives no boundary (Hartle-Hawking) wave function • This looks ‘holographic’. However in the standard formulation one has the gluing axiom: ‘Gluing axiom’: essential to get more complicated from simpler amplitudes Amplitude for bigger region = glued from amplitudes for smaller regions This could be / is also called ‘locality axiom’. -
Sheaf Theory
Sheaf Theory Anne Vaugon December 20, 2013 The goals of this talk are • to define a generalization denoted by RΓ(F) of de Rham cohomology; • to explain the notation RΓ(F) (here F is a sheaf and RΓ is a derived functor). 1 Presheaves and sheaves 1.1 Definitions and examples Let X be a topological space. Definition 1.1. A presheaf of k-modules F on X is defined by the following data: • a k-module F(U) for each open set U of X; • a map rUV : F(U) → F(V ) for each pair V ⊂ U of open subsets such that – rWV ◦ rVU = rWU for all open subsets W ⊂ V ⊂ U; – rUU = Id for all open subsets U. Therefore, a presheaf is a functor from the opposite category of open sets to the category of k-modules. If F is a presheaf, F(U) is called the set of sections of U and rVU the restriction from U to V . Definition 1.2. A presheaf F is a sheaf if • for any family (Ui)i∈I of open subsets of X • for any family of elements si ∈ F(Ui) such that rUi∩Uj ,Ui (si) = rUi∩Uj ,Uj (sj) for all i, j ∈ I there exists a unique s ∈ F(U) where U = ∪i∈I Ui such that rUi,U (s) = si for all i ∈ I. This means that we can extend a locally defined section. Definition 1.3. A morphism of presheaves f : F → G is a natural trans- formation between the functors F and G: for each open set U, there exists a morphism f(U): F(U) → G(U) such that the following diagram is commutative for V ⊂ U. -
The Smooth Locus in Infinite-Level Rapoport-Zink Spaces
The smooth locus in infinite-level Rapoport-Zink spaces Alexander Ivanov and Jared Weinstein February 25, 2020 Abstract Rapoport-Zink spaces are deformation spaces for p-divisible groups with additional structure. At infinite level, they become preperfectoid spaces. Let M8 be an infinite-level Rapoport-Zink space of ˝ ˝ EL type, and let M8 be one connected component of its geometric fiber. We show that M8 contains a dense open subset which is cohomologically smooth in the sense of Scholze. This is the locus of p-divisible groups which do not have any extra endomorphisms. As a corollary, we find that the cohomologically smooth locus in the infinite-level modular curve Xpp8q˝ is exactly the locus of elliptic curves E with supersingular reduction, such that the formal group of E has no extra endomorphisms. 1 Main theorem Let p be a prime number. Rapoport-Zink spaces [RZ96] are deformation spaces of p-divisible groups equipped with some extra structure. This article concerns the geometry of Rapoport-Zink spaces of EL type (endomor- phisms + level structure). In particular we consider the infinite-level spaces MD;8, which are preperfectoid spaces [SW13]. An example is the space MH;8, where H{Fp is a p-divisible group of height n. The points of MH;8 over a nonarchimedean field K containing W pFpq are in correspondence with isogeny classes of p-divisible groups G{O equipped with a quasi-isogeny G b O {p Ñ H b O {p and an isomorphism K OK K Fp K n Qp – VG (where VG is the rational Tate module). -
Bertini's Theorem on Generic Smoothness
U.F.R. Mathematiques´ et Informatique Universite´ Bordeaux 1 351, Cours de la Liberation´ Master Thesis in Mathematics BERTINI1S THEOREM ON GENERIC SMOOTHNESS Academic year 2011/2012 Supervisor: Candidate: Prof.Qing Liu Andrea Ricolfi ii Introduction Bertini was an Italian mathematician, who lived and worked in the second half of the nineteenth century. The present disser- tation concerns his most celebrated theorem, which appeared for the first time in 1882 in the paper [5], and whose proof can also be found in Introduzione alla Geometria Proiettiva degli Iperspazi (E. Bertini, 1907, or 1923 for the latest edition). The present introduction aims to informally introduce Bertini’s Theorem on generic smoothness, with special attention to its re- cent improvements and its relationships with other kind of re- sults. Just to set the following discussion in an historical perspec- tive, recall that at Bertini’s time the situation was more or less the following: ¥ there were no schemes, ¥ almost all varieties were defined over the complex numbers, ¥ all varieties were embedded in some projective space, that is, they were not intrinsic. On the contrary, this dissertation will cope with Bertini’s the- orem by exploiting the powerful tools of modern algebraic ge- ometry, by working with schemes defined over any field (mostly, but not necessarily, algebraically closed). In addition, our vari- eties will be thought of as abstract varieties (at least when over a field of characteristic zero). This fact does not mean that we are neglecting Bertini’s original work, containing already all the rele- vant ideas: the proof we shall present in this exposition, over the complex numbers, is quite close to the one he gave. -
Sheaves with Values in a Category7
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Topology Vol. 3, pp. l-18, Pergamon Press. 196s. F’rinted in Great Britain SHEAVES WITH VALUES IN A CATEGORY7 JOHN W. GRAY (Received 3 September 1963) $4. IN’IXODUCTION LET T be a topology (i.e., a collection of open sets) on a set X. Consider T as a category in which the objects are the open sets and such that there is a unique ‘restriction’ morphism U -+ V if and only if V c U. For any category A, the functor category F(T, A) (i.e., objects are covariant functors from T to A and morphisms are natural transformations) is called the category ofpresheaces on X (really, on T) with values in A. A presheaf F is called a sheaf if for every open set UE T and for every strong open covering {U,) of U(strong means {U,} is closed under finite, non-empty intersections) we have F(U) = Llim F( U,) (Urn means ‘generalized’ inverse limit. See $4.) The category S(T, A) of sheares on X with values in A is the full subcategory (i.e., morphisms the same as in F(T, A)) determined by the sheaves. In this paper we shall demonstrate several properties of S(T, A): (i) S(T, A) is left closed in F(T, A). (Theorem l(i), $8). This says that if a left limit (generalized inverse limit) of sheaves exists as a presheaf then that presheaf is a sheaf. -
SHEAVES of MODULES 01AC Contents 1. Introduction 1 2
SHEAVES OF MODULES 01AC Contents 1. Introduction 1 2. Pathology 2 3. The abelian category of sheaves of modules 2 4. Sections of sheaves of modules 4 5. Supports of modules and sections 6 6. Closed immersions and abelian sheaves 6 7. A canonical exact sequence 7 8. Modules locally generated by sections 8 9. Modules of finite type 9 10. Quasi-coherent modules 10 11. Modules of finite presentation 13 12. Coherent modules 15 13. Closed immersions of ringed spaces 18 14. Locally free sheaves 20 15. Bilinear maps 21 16. Tensor product 22 17. Flat modules 24 18. Duals 26 19. Constructible sheaves of sets 27 20. Flat morphisms of ringed spaces 29 21. Symmetric and exterior powers 29 22. Internal Hom 31 23. Koszul complexes 33 24. Invertible modules 33 25. Rank and determinant 36 26. Localizing sheaves of rings 38 27. Modules of differentials 39 28. Finite order differential operators 43 29. The de Rham complex 46 30. The naive cotangent complex 47 31. Other chapters 50 References 52 1. Introduction 01AD This is a chapter of the Stacks Project, version 77243390, compiled on Sep 28, 2021. 1 SHEAVES OF MODULES 2 In this chapter we work out basic notions of sheaves of modules. This in particular includes the case of abelian sheaves, since these may be viewed as sheaves of Z- modules. Basic references are [Ser55], [DG67] and [AGV71]. We work out what happens for sheaves of modules on ringed topoi in another chap- ter (see Modules on Sites, Section 1), although there we will mostly just duplicate the discussion from this chapter. -
Arxiv:1307.5568V2 [Math.AG]
PARTIAL POSITIVITY: GEOMETRY AND COHOMOLOGY OF q-AMPLE LINE BUNDLES DANIEL GREB AND ALEX KURONYA¨ To Rob Lazarsfeld on the occasion of his 60th birthday Abstract. We give an overview of partial positivity conditions for line bundles, mostly from a cohomological point of view. Although the current work is to a large extent of expository nature, we present some minor improvements over the existing literature and a new result: a Kodaira-type vanishing theorem for effective q-ample Du Bois divisors and log canonical pairs. Contents 1. Introduction 1 2. Overview of the theory of q-ample line bundles 4 2.1. Vanishing of cohomology groups and partial ampleness 4 2.2. Basic properties of q-ampleness 7 2.3. Sommese’s geometric q-ampleness 15 2.4. Ample subschemes, and a Lefschetz hyperplane theorem for q-ample divisors 17 3. q-Kodaira vanishing for Du Bois divisors and log canonical pairs 19 References 23 1. Introduction Ampleness is one of the central notions of algebraic geometry, possessing the extremely useful feature that it has geometric, numerical, and cohomological characterizations. Here we will concentrate on its cohomological side. The fundamental result in this direction is the theorem of Cartan–Serre–Grothendieck (see [Laz04, Theorem 1.2.6]): for a complete arXiv:1307.5568v2 [math.AG] 23 Jan 2014 projective scheme X, and a line bundle L on X, the following are equivalent to L being ample: ⊗m (1) There exists a positive integer m0 = m0(X, L) such that L is very ample for all m ≥ m0. (2) For every coherent sheaf F on X, there exists a positive integer m1 = m1(X, F, L) ⊗m for which F ⊗ L is globally generated for all m ≥ m1. -
Smoothness, Semi-Stability and Alterations
PUBLICATIONS MATHÉMATIQUES DE L’I.H.É.S. A. J. DE JONG Smoothness, semi-stability and alterations Publications mathématiques de l’I.H.É.S., tome 83 (1996), p. 51-93 <http://www.numdam.org/item?id=PMIHES_1996__83__51_0> © Publications mathématiques de l’I.H.É.S., 1996, tous droits réservés. L’accès aux archives de la revue « Publications mathématiques de l’I.H.É.S. » (http:// www.ihes.fr/IHES/Publications/Publications.html) implique l’accord avec les conditions géné- rales d’utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou im- pression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ SMOOTHNESS, SEMI-STABILITY AND ALTERATIONS by A. J. DE JONG* CONTENTS 1. Introduction .............................................................................. 51 2. Notations, conventions and terminology ...................................................... 54 3. Semi-stable curves and normal crossing divisors................................................ 62 4. Varieties.................................................................................. QQ 5. Alterations and curves ..................................................................... 76 6. Semi-stable alterations ..................................................................... 82 7. Group actions and alterations ............................................................. -
Notes on Categorical Logic
Notes on Categorical Logic Anand Pillay & Friends Spring 2017 These notes are based on a course given by Anand Pillay in the Spring of 2017 at the University of Notre Dame. The notes were transcribed by Greg Cousins, Tim Campion, L´eoJimenez, Jinhe Ye (Vincent), Kyle Gannon, Rachael Alvir, Rose Weisshaar, Paul McEldowney, Mike Haskel, ADD YOUR NAMES HERE. 1 Contents Introduction . .3 I A Brief Survey of Contemporary Model Theory 4 I.1 Some History . .4 I.2 Model Theory Basics . .4 I.3 Morleyization and the T eq Construction . .8 II Introduction to Category Theory and Toposes 9 II.1 Categories, functors, and natural transformations . .9 II.2 Yoneda's Lemma . 14 II.3 Equivalence of categories . 17 II.4 Product, Pullbacks, Equalizers . 20 IIIMore Advanced Category Theoy and Toposes 29 III.1 Subobject classifiers . 29 III.2 Elementary topos and Heyting algebra . 31 III.3 More on limits . 33 III.4 Elementary Topos . 36 III.5 Grothendieck Topologies and Sheaves . 40 IV Categorical Logic 46 IV.1 Categorical Semantics . 46 IV.2 Geometric Theories . 48 2 Introduction The purpose of this course was to explore connections between contemporary model theory and category theory. By model theory we will mostly mean first order, finitary model theory. Categorical model theory (or, more generally, categorical logic) is a general category-theoretic approach to logic that includes infinitary, intuitionistic, and even multi-valued logics. Say More Later. 3 Chapter I A Brief Survey of Contemporary Model Theory I.1 Some History Up until to the seventies and early eighties, model theory was a very broad subject, including topics such as infinitary logics, generalized quantifiers, and probability logics (which are actually back in fashion today in the form of con- tinuous model theory), and had a very set-theoretic flavour. -
Arxiv:2012.08669V1 [Math.CT] 15 Dec 2020 2 Preface
Sheaf Theory Through Examples (Abridged Version) Daniel Rosiak December 12, 2020 arXiv:2012.08669v1 [math.CT] 15 Dec 2020 2 Preface After circulating an earlier version of this work among colleagues back in 2018, with the initial aim of providing a gentle and example-heavy introduction to sheaves aimed at a less specialized audience than is typical, I was encouraged by the feedback of readers, many of whom found the manuscript (or portions thereof) helpful; this encouragement led me to continue to make various additions and modifications over the years. The project is now under contract with the MIT Press, which would publish it as an open access book in 2021 or early 2022. In the meantime, a number of readers have encouraged me to make available at least a portion of the book through arXiv. The present version represents a little more than two-thirds of what the professionally edited and published book would contain: the fifth chapter and a concluding chapter are missing from this version. The fifth chapter is dedicated to toposes, a number of more involved applications of sheaves (including to the \n- queens problem" in chess, Schreier graphs for self-similar groups, cellular automata, and more), and discussion of constructions and examples from cohesive toposes. Feedback or comments on the present work can be directed to the author's personal email, and would of course be appreciated. 3 4 Contents Introduction 7 0.1 An Invitation . .7 0.2 A First Pass at the Idea of a Sheaf . 11 0.3 Outline of Contents . 20 1 Categorical Fundamentals for Sheaves 23 1.1 Categorical Preliminaries . -
SHEAVES, TOPOSES, LANGUAGES Acceleration Based on A
Chapter 7 Logic of behavior: Sheaves, toposes, and internal languages 7.1 How can we prove our machine is safe? Imagine you are trying to design a system of interacting components. You wouldn’t be doing this if you didn’t have a goal in mind: you want the system to do something, to behave in a certain way. In other words, you want to restrict its possibilities to a smaller set: you want the car to remain on the road, you want the temperature to remain in a particular range, you want the bridge to be safe for trucks to pass. Out of all the possibilities, your system should only permit some. Since your system is made of components that interact in specified ways, the possible behavior of the whole—in any environment—is determined by the possible behaviors of each of its components in their local environments, together with the precise way in which they interact.1 In this chapter, we will discuss a logic wherein one can describe general types of behavior that occur over time, and prove properties of a larger-scale system from the properties and interaction patterns of its components. For example, suppose we want an autonomous vehicle to maintain a distance of some safe R from other objects. To do so, several components must interact: a 2 sensor that approximates the real distance by an internal variable S0, a controller that uses S0 to decide what action A to take, and a motor that moves the vehicle with an 1 The well-known concept of emergence is not about possibilities, it is about prediction.