Differential Geometry of Complex Vector Bundles
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Connections on Bundles Md
Dhaka Univ. J. Sci. 60(2): 191-195, 2012 (July) Connections on Bundles Md. Showkat Ali, Md. Mirazul Islam, Farzana Nasrin, Md. Abu Hanif Sarkar and Tanzia Zerin Khan Department of Mathematics, University of Dhaka, Dhaka 1000, Bangladesh, Email: [email protected] Received on 25. 05. 2011.Accepted for Publication on 15. 12. 2011 Abstract This paper is a survey of the basic theory of connection on bundles. A connection on tangent bundle , is called an affine connection on an -dimensional smooth manifold . By the general discussion of affine connection on vector bundles that necessarily exists on which is compatible with tensors. I. Introduction = < , > (2) In order to differentiate sections of a vector bundle [5] or where <, > represents the pairing between and ∗. vector fields on a manifold we need to introduce a Then is a section of , called the absolute differential structure called the connection on a vector bundle. For quotient or the covariant derivative of the section along . example, an affine connection is a structure attached to a differentiable manifold so that we can differentiate its Theorem 1. A connection always exists on a vector bundle. tensor fields. We first introduce the general theorem of Proof. Choose a coordinate covering { }∈ of . Since connections on vector bundles. Then we study the tangent vector bundles are trivial locally, we may assume that there is bundle. is a -dimensional vector bundle determine local frame field for any . By the local structure of intrinsically by the differentiable structure [8] of an - connections, we need only construct a × matrix on dimensional smooth manifold . each such that the matrices satisfy II. -
Vector Bundles on Projective Space
Vector Bundles on Projective Space Takumi Murayama December 1, 2013 1 Preliminaries on vector bundles Let X be a (quasi-projective) variety over k. We follow [Sha13, Chap. 6, x1.2]. Definition. A family of vector spaces over X is a morphism of varieties π : E ! X −1 such that for each x 2 X, the fiber Ex := π (x) is isomorphic to a vector space r 0 0 Ak(x).A morphism of a family of vector spaces π : E ! X and π : E ! X is a morphism f : E ! E0 such that the following diagram commutes: f E E0 π π0 X 0 and the map fx : Ex ! Ex is linear over k(x). f is an isomorphism if fx is an isomorphism for all x. A vector bundle is a family of vector spaces that is locally trivial, i.e., for each x 2 X, there exists a neighborhood U 3 x such that there is an isomorphism ': π−1(U) !∼ U × Ar that is an isomorphism of families of vector spaces by the following diagram: −1 ∼ r π (U) ' U × A (1.1) π pr1 U −1 where pr1 denotes the first projection. We call π (U) ! U the restriction of the vector bundle π : E ! X onto U, denoted by EjU . r is locally constant, hence is constant on every irreducible component of X. If it is constant everywhere on X, we call r the rank of the vector bundle. 1 The following lemma tells us how local trivializations of a vector bundle glue together on the entire space X. -
Lecture 3. Resolutions and Derived Functors (GL)
Lecture 3. Resolutions and derived functors (GL) This lecture is intended to be a whirlwind introduction to, or review of, reso- lutions and derived functors { with tunnel vision. That is, we'll give unabashed preference to topics relevant to local cohomology, and do our best to draw a straight line between the topics we cover and our ¯nal goals. At a few points along the way, we'll be able to point generally in the direction of other topics of interest, but other than that we will do our best to be single-minded. Appendix A contains some preparatory material on injective modules and Matlis theory. In this lecture, we will cover roughly the same ground on the projective/flat side of the fence, followed by basics on projective and injective resolutions, and de¯nitions and basic properties of derived functors. Throughout this lecture, let us work over an unspeci¯ed commutative ring R with identity. Nearly everything said will apply equally well to noncommutative rings (and some statements need even less!). In terms of module theory, ¯elds are the simple objects in commutative algebra, for all their modules are free. The point of resolving a module is to measure its complexity against this standard. De¯nition 3.1. A module F over a ring R is free if it has a basis, that is, a subset B ⊆ F such that B generates F as an R-module and is linearly independent over R. It is easy to prove that a module is free if and only if it is isomorphic to a direct sum of copies of the ring. -
Arithmetic Duality Theorems
Arithmetic Duality Theorems Second Edition J.S. Milne Copyright c 2004, 2006 J.S. Milne. The electronic version of this work is licensed under a Creative Commons Li- cense: http://creativecommons.org/licenses/by-nc-nd/2.5/ Briefly, you are free to copy the electronic version of the work for noncommercial purposes under certain conditions (see the link for a precise statement). Single paper copies for noncommercial personal use may be made without ex- plicit permission from the copyright holder. All other rights reserved. First edition published by Academic Press 1986. A paperback version of this work is available from booksellers worldwide and from the publisher: BookSurge, LLC, www.booksurge.com, 1-866-308-6235, [email protected] BibTeX information @book{milne2006, author={J.S. Milne}, title={Arithmetic Duality Theorems}, year={2006}, publisher={BookSurge, LLC}, edition={Second}, pages={viii+339}, isbn={1-4196-4274-X} } QA247 .M554 Contents Contents iii I Galois Cohomology 1 0 Preliminaries............................ 2 1 Duality relative to a class formation . ............. 17 2 Localfields............................. 26 3 Abelianvarietiesoverlocalfields.................. 40 4 Globalfields............................. 48 5 Global Euler-Poincar´echaracteristics................ 66 6 Abelianvarietiesoverglobalfields................. 72 7 An application to the conjecture of Birch and Swinnerton-Dyer . 93 8 Abelianclassfieldtheory......................101 9 Otherapplications..........................116 AppendixA:Classfieldtheoryforfunctionfields............126 -
Formal GAGA for Good Moduli Spaces
FORMAL GAGA FOR GOOD MODULI SPACES ANTON GERASCHENKO AND DAVID ZUREICK-BROWN Abstract. We prove formal GAGA for good moduli space morphisms under an assumption of “enough vector bundles” (which holds for instance for quotient stacks). This supports the philoso- phy that though they are non-separated, good moduli space morphisms largely behave like proper morphisms. 1. Introduction Good moduli space morphisms are a common generalization of good quotients by linearly re- ductive group schemes [GIT] and coarse moduli spaces of tame Artin stacks [AOV08, Definition 3.1]. Definition ([Alp13, Definition 4.1]). A quasi-compact and quasi-separated morphism of locally Noetherian algebraic stacks φ: X → Y is a good moduli space morphism if • (φ is Stein) the morphism OY → φ∗OX is an isomorphism, and • (φ is cohomologically affine) the functor φ∗ : QCoh(OX ) → QCoh(OY ) is exact. If φ: X → Y is such a morphism, then any morphism from X to an algebraic space factors through φ [Alp13, Theorem 6.6].1 In particular, if there exists a good moduli space morphism φ: X → X where X is an algebraic space, then X is determined up to unique isomorphism. In this case, X is said to be the good moduli space of X . If X = [U/G], this corresponds to X being a good quotient of U by G in the sense of [GIT] (e.g. for a linearly reductive G, [Spec R/G] → Spec RG is a good moduli space). In many respects, good moduli space morphisms behave like proper morphisms. They are uni- versally closed [Alp13, Theorem 4.16(ii)] and weakly separated [ASvdW10, Proposition 2.17], but since points of X can have non-proper stabilizer groups, good moduli space morphisms are gen- erally not separated (e.g. -
A Algebraic Varieties
A Algebraic Varieties A.1 Basic definitions Let k[X1,X2,...,Xn] be a polynomial algebra over an algebraically closed field k with n indeterminates X1,...,Xn. We sometimes abbreviate it as k[X]= k[X1,X2,...,Xn]. Let us associate to each polynomial f(X)∈ k[X] its zero set n V(f):= {x = (x1,x2,...,xn) ∈ k | f(x)= f(x1,x2,...,xn) = 0} n 2in the n-fold product set k of k. For any subset S ⊂ k[X] we also set V(S) = f ∈S V(f). Then we have the following properties: n (i) 2V(1) =∅,V(0) =k . = (ii) i∈I V(Si) V( i∈I Si). (iii) V(S1) ∪ V(S2) = V(S1S2), where S1S2 := {fg | f ∈ S1,g∈ S2}. The inclusion ⊂ of (iii) is clear. We will prove only the inclusion ⊃. For x ∈ V(S1S2) \ V(S2) there is an element g ∈ S2 such that g(x) = 0. On the other hand, it ∀ ∀ follows from x ∈ V(S1S2) that f(x)g(x) = 0( f ∈ S1). Hence f(x)= 0( f ∈ S1) and x ∈ V(S1). So the part ⊃ was also proved. By (i), (ii), (iii) the set kn is endowed with the structure of a topological space by taking {V(S) | S ⊂ k[X]} to be its closed subsets. We call this topology of kn the Zariski topology. The closed subsets V(S) of kn with respect to it are called algebraic sets in kn. Note that V(S)= V(S), where S denotes the ideal of k[X] generated by S. -
Flat Vector Bundles and Analytic Torsion on Orbifolds
i “Orbifold_Torsion_final” — 2020/9/10 — 0:54 — page 1 — #1 i i i Communications in Analysis and Geometry Volume 00, Number 0, 1–85, 0000 Flat vector bundles and analytic torsion on orbifolds Shu Shen and Jianqing Yu This article is devoted to a study of flat orbifold vector bundles. We construct a bijection between the isomorphic classes of proper flat orbifold vector bundles and the equivalence classes of represen- tations of the orbifold fundamental groups of base orbifolds. We establish a Bismut-Zhang like anomaly formula for the Ray-Singer metric on the determinant line of the cohomology of a compact orb- ifold with coefficients in an orbifold flat vector bundle. We show that the analytic torsion of an acyclic unitary flat orbifold vector bundle is equal to the value at zero of a dynamical zeta function when the underlying orbifold is a compact locally symmetric space of reductive type, which extends one of the results obtained by the first author for compact locally symmetric manifolds. Introduction 3 1 Preliminary 10 1.1 Determinants 11 1.2 Group actions 11 1.3 Characteristic forms on manifolds 11 2 Topology of orbifolds 15 arXiv:1704.08369v3 [math.DG] 9 Sep 2020 2.1 Definition of orbifolds 15 2.2 Singular set of orbifolds 21 2.3 Orbifold vector bundle 22 1 i i i i i “Orbifold_Torsion_final” — 2020/9/10 — 0:54 — page 2 — #2 i i i 2 S. Shen and J. Yu 2.4 Orbifold fundamental groups and universal covering orbifold 26 2.5 Flat vector bundles and holonomy 32 3 Differential calculus on orbifolds 35 3.1 Differential operators on orbifolds 36 3.2 -
Arxiv:2008.10677V3 [Math.CT] 9 Jul 2021 Space Ha Hoyepiil Ea Ihtewr Fj Ea N194 in Leray J
On sheaf cohomology and natural expansions ∗ Ana Luiza Tenório, IME-USP, [email protected] Hugo Luiz Mariano, IME-USP, [email protected] July 12, 2021 Abstract In this survey paper, we present Čech and sheaf cohomologies – themes that were presented by Koszul in University of São Paulo ([42]) during his visit in the late 1950s – we present expansions for categories of generalized sheaves (i.e, Grothendieck toposes), with examples of applications in other cohomology theories and other areas of mathematics, besides providing motivations and historical notes. We conclude explaining the difficulties in establishing a cohomology theory for elementary toposes, presenting alternative approaches by considering constructions over quantales, that provide structures similar to sheaves, and indicating researches related to logic: constructive (intuitionistic and linear) logic for toposes, sheaves over quantales, and homological algebra. 1 Introduction Sheaf Theory explicitly began with the work of J. Leray in 1945 [46]. The nomenclature “sheaf” over a space X, in terms of closed subsets of a topological space X, first appeared in 1946, also in one of Leray’s works, according to [21]. He was interested in solving partial differential equations and build up a strong tool to pass local properties to global ones. Currently, the definition of a sheaf over X is given by a “coherent family” of structures indexed on the lattice of open subsets of X or as étale maps (= local homeomorphisms) into X. Both arXiv:2008.10677v3 [math.CT] 9 Jul 2021 formulations emerged in the late 1940s and early 1950s in Cartan’s seminars and, in modern terms, they are intimately related by an equivalence of categories. -
Invariant Metrics on Negatively Pinched Complete Kähler Manifolds
INVARIANT METRICS ON NEGATIVELY PINCHED COMPLETE KAHLER¨ MANIFOLDS DAMIN WU AND SHING{TUNG YAU Abstract. We prove that a complete K¨ahlermanifold with holomorphic curvature bounded between two negative constants admits a unique complete K¨ahler-Einstein metric. We also show this metric and the Kobayashi-Royden metric are both uni- formly equivalent to the background K¨ahler metric. Furthermore, all three metrics are shown to be uniformly equivalent to the Bergman metric, if the complete K¨ahler manifold is simply-connected, with the sectional curvature bounded between two negative constants. In particular, we confirm two conjectures of R. E. Greene and H. Wu posted in 1979. Table of Contents 1. Introduction1 2. Effective quasi-bounded geometry5 3. Wan-Xiong Shi's Lemmas 13 Appendix A. Maximum principles 16 4. Kobayashi-Royden metric and holomorphic curvature 19 5. Bergman metric and sectional curvature 21 6. K¨ahler-Einsteinmetric and holomorphic curvature 28 References 31 1. Introduction The classical Liouville's theorem tells us that the complex plane C has no bounded nonconstant holomorphic functions, while, by contrast, the unit disk D has plenty of bounded nonconstant holomorphic functions. From a geometric viewpoint, the complex plane does not admit any metric of negative bounded-away-from-zero curva- ture, while the unit disk admits a metric, the Poincar´emetric, of constant negative curvature. The first author was partially supported by the NSF grant DMS-1611745. The second author was partially supported by the NSF grant DMS-1308244 and DMS-1607871. The first author would like to thank Professor H. Wu for bringing his attention to the Bergman metric in 2006. -
2 Sheaves and Cohomology
2 Sheaves and Cohomology 2.1 Sheaves and Presheaves We fix a topological space X. Later we will include assumptions that are satisfied by smooth manifolds. 2.1.1 Definitions and Examples Definition 2.1. A presheaf of abelian groups F on X assigns to each open U ⊆ X an abelian group F (U) = Γ(U; F ) and for every inclusion of open sets V ⊆ U a homomorphism of abelian groups F ρUV : F (U) ! F (V ), often called the restriction map, satisfying F 1 [P1] ρUU = F(U) F F F [P2] for W ⊆ V ⊆ U, we have ρVW ◦ ρUV = ρUW . If F and G are two presheaves (of abelian groups) on X, then a morphism ' : F ! G consists of the data of a morphism 'U : F (U) ! G (U) for each open set U ⊆ X such that if V ⊆ U is an inclusion, then we have commutative diagrams 'U F (U) / G (U) F G ρUV ρUV (V ) / (V ): F 'V G Remark 2.2. We may form a category TopX whose objects are open sets in X and whose mor- phisms are simply inclusions of open sets. Then the above definition says that a presheaf is a ◦ contravariant functor TopX ! Ab, and that a morphism of presheaves is a natural transforma- tion of the associated functors. Definition 2.3. A sheaf F of abelian groups on X is a presheaf which, for any open set U ⊆ X and any open covering fUigi2I of U, satisfies the two additional properties: [S1] if s 2 F (U) is such that sjUi = 0 for all i 2 I, then s = 0; [S2] if si 2 F (Ui) such that sijUi\Uj = sjjUi\Uj for all i; j 2 I, then there exists s 2 F (U) such that sjUi = si for each i. -
Flat ^Bundles with Canonical Metrics
J. DIFFERENTIAL GEOMETRY 28 (1988) 361-382 FLAT ^BUNDLES WITH CANONICAL METRICS KEVIN CORLETTE 1. Introduction A great deal of attention has recently been focused on the relationship between the invariant theory of semisimple algebraic group actions on complex algebraic varieties an(J the behavior of the moment map and quantum data provided by an associated symplectic structure. In particular, it has been shown that the moment map has zero as a regular value precisely when there are stable points, in the sense of geometric invariant theory [13]. This paper discusses an infinite dimensional instance of this correspondence involving flat bundles over compact Riemannian manifolds. In finite dimensions, this philosophy received its simplest, and earliest, exposition in [11]. There, Kempf and Ness considered the case of a represen- tation of a semisimple algebraic group G over C on a complex vector space V with some positive definite Hermitian form. Geometric invariant theory picks out a class of G-orbits called the stable ones. To be specific, υ G V is stable if its orbit is closed in V and has the maximum possible dimension. Kempf and Ness observed that Gυ is closed in V if and only if it contains a shortest vector. On the other side of the ledger, there is a symplectic structure on V associated with the chosen Hermitian form, and one has the action of the compact subgroup of G which preserves this form. There is a moment map associated with this action, and it turns out that the vanish- ing of this map at υ is equivalent to v being the shortest vector in its orbit under G. -
Arxiv:1710.06183V2 [Math.AG]
ALGEBRAIC INTEGRABILITY OF FOLIATIONS WITH NUMERICALLY TRIVIAL CANONICAL BUNDLE ANDREAS HÖRING AND THOMAS PETERNELL Abstract. Given a reflexive sheaf on a mildly singular projective variety, we prove a flatness criterion under certain stability conditions. This implies the algebraicity of leaves for sufficiently stable foliations with numerically trivial canonical bundle such that the second Chern class does not vanish. Combined with the recent work of Druel and Greb-Guenancia-Kebekus this establishes the Beauville-Bogomolov decomposition for minimal models with trivial canon- ical class. 1. introduction 1.A. Main result. Let X be a normal complex projective variety that is smooth in codimension two, and let E be a reflexive sheaf on X. If E is slope-stable with respect to some ample divisor H of slope µH (E)=0, then a famous result of Mehta-Ramanathan [MR84] says that the restriction EC to a general complete intersection C of sufficiently ample divisors is stable and nef. On the other hand the variety X contains many dominating families of irreducible curves to which Mehta-Ramanathan does not apply; therefore one expects that, apart from very special situations, EC will not be nef for many curves C. If E is locally free, denote by π : P(E) → X the projectivisation of E and by ζ := c1(OP(E)(1)) the tautological class on P(E). The nefness of EC then translates into the nefness of the restriction of ζ to P(EC). Thus, the stability of E implies some positivity of the tautological class ζ. On the other hand, the non-nefness of EC on many curves can be rephrased by saying that the tautological class ζ should not be pseudoeffective.