Notes on 4-Manifolds
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Automorphic Forms for Some Even Unimodular Lattices
AUTOMORPHIC FORMS FOR SOME EVEN UNIMODULAR LATTICES NEIL DUMMIGAN AND DAN FRETWELL Abstract. We lookp at genera of even unimodular lattices of rank 12p over the ring of integers of Q( 5) and of rank 8 over the ring of integers of Q( 3), us- ing Kneser neighbours to diagonalise spaces of scalar-valued algebraic modular forms. We conjecture most of the global Arthur parameters, and prove several of them using theta series, in the manner of Ikeda and Yamana. We find in- stances of congruences for non-parallel weight Hilbert modular forms. Turning to the genus of Hermitian lattices of rank 12 over the Eisenstein integers, even and unimodular over Z, we prove a conjecture of Hentschel, Krieg and Nebe, identifying a certain linear combination of theta series as an Hermitian Ikeda lift, and we prove that another is an Hermitian Miyawaki lift. 1. Introduction Nebe and Venkov [54] looked at formal linear combinations of the 24 Niemeier lattices, which represent classes in the genus of even, unimodular, Euclidean lattices of rank 24. They found a set of 24 eigenvectors for the action of an adjacency oper- ator for Kneser 2-neighbours, with distinct integer eigenvalues. This is equivalent to computing a set of Hecke eigenforms in a space of scalar-valued modular forms for a definite orthogonal group O24. They conjectured the degrees gi in which the (gi) Siegel theta series Θ (vi) of these eigenvectors are first non-vanishing, and proved them in 22 out of the 24 cases. (gi) Ikeda [37, §7] identified Θ (vi) in terms of Ikeda lifts and Miyawaki lifts, in 20 out of the 24 cases, exploiting his integral construction of Miyawaki lifts. -
Genus of Vertex Algebras and Mass Formula
Genus of vertex algebras and mass formula Yuto Moriwaki * Graduate School of Mathematical Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8914, Japan Abstract. We introduce the notion of a genus and its mass for vertex algebras. For lattice vertex algebras, their genera are the same as those of lattices, which play an important role in the classification of lattices. We derive a formula relating the mass for vertex algebras to that for lattices, and then give a new characterization of some holomorphic vertex operator algebras. Introduction Vertex operator algebras (VOAs) are algebraic structures that play an important role in two-dimensional conformal field theory. The classification of conformal field theories is an extremely interesting problem, of importance in mathematics, statistical mechanics, and string theory; Mathematically, it is related to the classification of vertex operator algebras, which is a main theme of this work. An important class of vertex operator algebras can be constructed from positive-definite even integral lattices, called lattice vertex algebras [Bo1, LL, FLM]. In this paper, we propose a new method to construct and classify vertex algebras by using a method developed in the study of lattices. A lattice is a finite rank free abelian group equipped with a Z-valued symmetric bilinear form. Two such lattices are equivalent (or in the same genus) if they are isomorphic over the ring of p-adic integers Zp for each prime p and also equivalent over the real number arXiv:2004.01441v2 [math.QA] 5 Mar 2021 field R. Lattices in the same genus are not always isomorphic over Z. -
A Survey of the Foundations of Four-Manifold Theory in the Topological Category
A SURVEY OF THE FOUNDATIONS OF FOUR-MANIFOLD THEORY IN THE TOPOLOGICAL CATEGORY STEFAN FRIEDL, MATTHIAS NAGEL, PATRICK ORSON, AND MARK POWELL Abstract. The goal of this survey is to state some foundational theorems on 4-manifolds, especially in the topological category, give precise references, and provide indications of the strategies employed in the proofs. Where appropriate we give statements for manifolds of all dimensions. 1. Introduction Here and throughout the paper \manifold" refers to what is often called a \topological manifold"; see Section 2 for a precise definition. Here are some of the statements discussed in this article. (1) Existence and uniqueness of collar neighbourhoods (Theorem 2.5). (2) The Isotopy Extension theorem (Theorem 2.10). (3) Existence of CW structures (Theorem 4.5). (4) Multiplicativity of the Euler characteristic under finite covers (Corollary 4.8). (5) The Annulus theorem 5.1 and the Stable Homeomorphism Theorem 5.3. (6) Connected sum of two oriented connected 4-manifolds is well-defined (Theorem 5.11). (7) The intersection form of the connected sum of two 4-manifolds is the sum of the intersection forms of the summands (Proposition 5.15). (8) Existence and uniqueness of tubular neighbourhoods of submanifolds (Theorems 6.8 and 6.9). (9) Noncompact connected 4-manifolds admit a smooth structure (Theorem 8.1). (10) When the Kirby-Siebenmann invariant of a 4-manifold vanishes, both connected sum with copies of S2 S2 and taking the product with R yield smoothable manifolds (Theorem 8.6). × (11) Transversality for submanifolds and for maps (Theorems 10.3 and 10.8). -
1 Positive Definite Even Unimodular Lattices
Algebraic automorphic forms and Hilbert-Siegel modular forms Tamotsu Ikeda (Kyoto university) Sep. 17, 2018, at Hakuba 1 Positive definite even unimodular lattices Let F be a totally real number field of degree d. Let n > 0 be an integer such that dn is even. Then, by Minkowski-Hasse theorem, there exists a quadratic space (Vn;Q) of rank 4n with the following properties: (1) (V; Q) is unramified at any non-archimedean place. (2) (V; Q) is positive definite ai any archimedean place. Definition 1. An algebraic automorphic form on the orthogonal group OQ is a locally constant function on OQ(F )nOQ(A). Put 1 (x; y) = (Q(x + y) − Q(x) − Q(y)) x; y 2 V: Q 2 Let L be a o-lattie in V (F ). The dual lattice L∗ is defined by ∗ L = fx 2 Vn(F ) j (x; L)Q ⊂ og: Then L is an integral lattice if and only if L ⊂ L∗. An integral lattice L is called an even lattice if Q(x) ⊂ 2o 8x 2 L: Moreover, an integral lattice L is unimodular if L = L∗. By the assumption (1) and (2), there exists a positive definite even unimodular latice L0 in V (F ). Two integral lattices L1 and L2 are equivalent if there exists an element g 2 OQ(F ) such that g · L1 = L2. Two integral lattices L1 and L2 are in the same genus if there 1 exists an element gv 2 OQ(Fv) such that g · L1;v = L2;v for any finite place v. The set of positive definite even unimodular lattices in V (F ) form a genus. -
Lattice Theory, K3 Surfaces, and the Torelli Theorem
UMass, Reading Seminar in Algebraic Geometry, Lattice theory, K3 surfaces, and the Torelli theorem Luca Schaffler October 4, 2019 1 What is a lattice? Definition 1.1. A lattice is a pair (L; ·), where L is a finitely generated free abelian group and ·: L × L ! Z such that (v; w) 7! v · w is a symmetric bilinear form. • L is even if v2 := v · v is an even number for all v 2 L. • The Gram matrix of L with respect to a basis fe1; : : : ; eng for L is the matrix of intersection (ei · ej)1≤i;j≤n. • The rank of L is defined to be the rank of one of its Gram matrices. • A lattice L is unimodular if the determinant of one of its Gram matrices is ±1. Equivalently, L of maximal rank is unimodular provided the discriminant group ∗ ∗ L =L is trivial (we let L = HomZ(L; Z)). • We can define the signature of L as the signature of one of its Gram matrices. By saying signature (a; b), we mean that a (resp. b) is the number of positive (resp. negative) eigenvalues. If L has signature (a; b), then we say that L is indefinite provided a; b > 0. 2 Example 1.2. U = (Z ; ·) with (v1; v2) · (w1; w2) = v1w2 + v2w1 is called the hyperbolic plane. Check that this is even, unimodular, and of signature (1; 1). 1 8 Example 1.3. E8 = (Z ;B), where 0 −2 1 0 0 0 0 0 0 1 B 1 −2 1 0 0 0 0 0 C B C B 0 1 −2 1 0 0 0 0 C B C B 0 0 1 −2 1 0 0 0 C B = B C : B 0 0 0 1 −2 1 0 1 C B C B 0 0 0 0 1 −2 1 0 C B C @ 0 0 0 0 0 1 −2 0 A 0 0 0 0 1 0 0 −2 This matrix can be reconstructed from the E8 Dynkin diagram. -
Arxiv:2001.07094V3 [Math.NT] 10 May 2021 Aeo Nirdcbeplnma)Alclgoa Principl a Local-Global Conditions, a Local Polynomial) I Are Irreducible Mcmullen 20]
ISOMETRIES OF LATTICES AND HASSE PRINCIPLES EVA BAYER-FLUCKIGER Abstract. We give necessary and sufficient conditions for an integral polynomial without linear factors to be the characteristic polynomial of an isometry of some even, unimodular lattice of given signature. This gives rise to Hasse principle questions, which we answer in a more general setting. As an application, we prove a Hasse principle for signatures of knots. 0. Introduction In [GM 02], Gross and McMullen give necessary conditions for a monic, irreducible polynomial to be the characteristic polynomial of an isometry of some even, unimodular lattice of prescribed signature. They speculate that these conditions may be sufficient; this is proved in [BT 20]. It turns out that the conditions of Gross and McMullen are local conditions, and that (in the case of an irreducible polynomial) a local-global principle holds. More generally, if F Z[X] is a monic polynomial without linear factors, the conditions of Gross∈ and McMullen are still necessary. Moreover, they are also sufficient everywhere locally (see Theorem 25.6). However, when F is reducible, the local-global principle no longer holds in general, as shown by the following example Example. Let F be the polynomial (X6 + X5 + X4 + X3 + X2 + X + 1)2(X6 X5 + X4 X3 + X2 X + 1)2, arXiv:2001.07094v3 [math.NT] 10 May 2021 − − − and let L be an even, unimodular, positive definite lattice of rank 24. The lattice L has an isometry with characteristic polynomial F everywhere locally, but not globally (see Example 25.17). In particular, the Leech lattice has no isometry with characteristic polynomial F , in spite of having such an isometry everywhere locally. -
Weil's Conjecture for Function Fields
Weil’s Conjecture for Function Fields February 12, 2019 1 First Lecture: The Mass Formula and Weil’s Conjecture Let R be a commutative ring and let V be an R-module. A quadratic form on V is a map q : V Ñ R satisfying the following conditions: paq The construction pv, wq ÞÑ qpv ` wq ´ qpvq ´ qpwq determines an R-bilinear map V ˆ V Ñ R. pbq For every element λ P R and every v P V , we have qpλvq “ λ2qpvq. A quadratic space over R is a pair pV, qq, where V is a finitely generated projective R-module and q is a quadratic form on V . One of the basic problems in the theory of quadratic forms can be formulated as follows: Question 1.1. Let R be a commutative ring. Can one classify quadratic spaces over R (up to isomorphism)? Let us begin by describing some cases where Question 1.1 admits a complete answer. Example 1.2 (Quadratic Forms over C). Let R “ C be the field of complex numbers (or, more generally, any algebraically closed field of characteristic different from 2). Then every quadratic space over R is isomorphic to pCn, qq, where q is given by the formula 2 2 qpx1, . , xnq “ x1 ` ¨ ¨ ¨ ` xr for some 0 ¤ r ¤ n. Moreover, the integer r is uniquely determined: it is an isomorphism- invariant called the rank of the quadratic form q. Example 1.3 (Quadratic Forms over the Real Numbers). Let R “ R be the field of real numbers. Then every quadratic space over R is isomorphic to pRn, qq, where the quadratic form q is given by 2 2 2 2 2 qpx1, . -
Dynamics on K3 Surfaces: Salem Numbers and Siegel Disks
Dynamics on K3 surfaces: Salem numbers and Siegel disks Curtis T. McMullen 19 January, 2001 Abstract This paper presents the first examples of K3 surface automorphisms f : X X with Siegel disks (domains on which f acts by an irrational rotation).→ The set of such examples is countable, and the surface X must be non-projective to carry a Siegel disk. These automorphisms are synthesized from Salem numbers of de- gree 22 and trace 1, which play the role of the leading eigenvalue for f ∗ H2(X). The construction− uses the Torelli theorem, the Atiyah-Bott fixed-point| theorem and results from transcendence theory. Contents 1 Introduction............................ 1 2 K3surfaces ............................ 7 3 AutomorphismsofK3surfaces . 11 4 ErgodicdynamicsonKummersurfaces. 14 5 Siegel disks and transcendence theory . 18 6 HolomorphicLefschetznumbers. 20 7 SiegeldisksonK3surfaces. 22 8 Latticesinnumberfields. 24 9 From Salem numbers to automorphisms . 29 10 ExamplesofSiegeldisks . 30 11 Limits of K¨ahler-Einstein metrics . 34 Research supported in part by the NSF. 2000 Mathematics Subject Classification: 37F50 (11R06, 14J50, 32H50). 1 Introduction The first dynamically interesting automorphisms of compact complex man- ifolds arise on K3 surfaces. Indeed, automorphisms of curves are linear (genus 0 or 1) or of finite order (genus 2 or more). Similarly, automorphisms of most surfaces (includ- ing P2, surfaces of general type and ruled surfaces) are either linear, finite order or skew-products over automorphisms of curves. Only K3 surfaces, Enriques surfaces, complex tori and certain non-minimal rational surfaces admit automorphisms of positive topological entropy [Ca2]. The automor- phisms of tori are linear, and the Enriques examples are double-covered by K3 examples. -
Kneser Neighbors and Orthogonal Galois Representations In
Kneser neighbours and orthogonal Galois representations in dimensions 16 and 24 Gaetan¨ Chenevier (joint work with Jean Lannes) Let n ≥ 1 be an integer. Recall that an even unimodular lattice in the standard euclidean space Rn is a lattice L ⊂ Rn of covolume 1 with x · x ∈ 2Z for all x ∈ L. n Let Xn denote the set of isometry classes of even unimodular lattices in R . As is well-known, Xn is a finite set which is non-empty if and only if n ≡ 0 mod 8. For example, the lattice e + ... + e E = D + 1 n , n n Z 2 n {e1, . , en} denoting the canonical basis of R and Dn the sublattice of index n P 2 in Z whose elements (xi) satisfy i xi ≡ 0 mod 2, is even unimodular for n ≡ 0 mod 8. The set Xn has been determined in only three cases. One has X8 = {E8} (Mordell), X16 = {E8 ⊕ E8, E16} (Witt) and Niemeier showed that X24 has 24 explicit elements (see [V]). The number of numerical coincidences related to Niemeier’s lists is quite extraordinary and makes that list still mysterious. For the other values of n the Minkowski-Siegel-Smith mass formula shows that Xn is huge, perhaps impossible to describe. For instance, X32 already has more than 80.106 elements ([S]). Let L ⊂ Rn be an even unimodular lattice, and let p be a prime; Kneser defines a p-neighbour of L as an even unimodular lattice M ⊂ Rn such that M ∩ L has index p in L (hence in M). -
On Extremal Even Unimodular 72-Dimensional Lattices 1491
MATHEMATICS OF COMPUTATION Volume 83, Number 287, May 2014, Pages 1489–1494 S 0025-5718(2013)02744-5 Article electronically published on July 16, 2013 ON EXTREMAL EVEN UNIMODULAR 72-DIMENSIONAL LATTICES GABRIELE NEBE AND RICHARD PARKER Abstract. By computer search we show that the lattice Γ of Nebe (2012) is the unique extremal even unimodular 72-dimensional lattices that can be constructed as proposed by Griess (2010). 1. Introduction In this paper a lattice (L, Q) is always an even unimodular positive definite lattice, i.e., a free Z-module L equipped with an integral positive definite quadratic form Q : L → Z of determinant 1. The minimum of L is the minimum of the quadratic form on the non-zero vectors of L, min(L)=min(L, Q)=min{Q() | 0 = ∈ L}1. From the theory of modular forms it is known that the minimum of an even unimod- n ular lattice of dimension n is at most 24 +1. Lattices achieving equality are called extremal. Of particular interest are extremal unimodular lattices in the “jump di- mensions” — the multiples of 24. There are five extremal even unimodular lattices known in the jump dimensions, the Leech lattice Λ24, the unique even unimodular 2 3 lattice in dimension 24 without roots, three lattices called P48p, P48q, P48n, of dimension 48 which have minimum 3 ([2], [8]) and one lattice Γ in dimension 72 ([9]). If (L, Q) is an even unimodular lattice, then L/2L becomes a non-degenerate quadratic space over F2 with quadratic form q( +2L):=Q()+2Z. -
Even Unimodular 12-Dimensional Quadratic Forms Over C!(D)
ADVANCES IN MATHEMATICS 64, 241-278 (1987) Even Unimodular 12-Dimensional Quadratic Forms over C!(d) PATRICK J. COSTELLO Department of Mathematics, Eastern Kentucky University, Richmond, Kentucky 40475 AND JOHN S. HSIA* Department of Mathematics, Ohio State University, Columbus, Ohio 43210 A complete list of all 1Zdimensional even unimodular lattices over Q(3) is given. Theta series are used to verify that the list of those with 2-vectors is complete. It is proved that there is a unique lattice with no 2-vectors and the Siegel mass for- mula gives the order of its automorphism group. 0 1987 Academic Press, Inc. Positive definite integral quadratic forms or, in the modern terminology, positive definite integral lattices have a long and interesting history with applications and connections to many branches of mathematics including modular form theory, group theory, Lie theory, and coding theory. One fundamental problem in the study of lattices is the complete classification of all lattices of a given discriminant and rank. The problem of classifying these lattices over Z has been studied by many people. It is well known that even unimodular Z-lattices exist only in dimensions which are multiples of 8. A complete classification of even unimodular Z-lattices is only known for dimensions 8, 16, and 24. There is precisely one 8-dimensional even unimodular Z-lattice which is commonly denoted by E8 (in the notation for exceptional Lie groups). It was first dis- covered by Korkine and Zolotareff [KZ] in 1873 although its existence was already nonconstructively known to Smith [S] in 1867. Mordell * This research was supported in part by the National Science Foundation under Grants MCS-8202065 and DMS-8503326. -
Fivebranes and 4-Manifolds
Preprint typeset in JHEP style - HYPER VERSION Fivebranes and 4-manifolds Abhijit Gadde1, Sergei Gukov1,2, and Pavel Putrov1 1 California Institute of Technology, Pasadena, CA 91125, USA 2 Max-Planck-Institut f¨ur Mathematik, Vivatsgasse 7, D-53111 Bonn, Germany Abstract: We describe rules for building 2d theories labeled by 4-manifolds. Using the proposed dictionary between building blocks of 4-manifolds and 2d = (0, 2) theories, N we obtain a number of results, which include new 3d = 2 theories T [M ] associated N 3 with rational homology spheres and new results for Vafa-Witten partition functions on 4-manifolds. In particular, we point out that the gluing measure for the latter is precisely the superconformal index of 2d (0, 2) vector multiplet and relate the basic building blocks with coset branching functions. We also offer a new look at the fusion of defect lines / walls, and a physical interpretation of the 4d and 3d Kirby calculus as dualities of 2d = (0, 2) N theories and 3d = 2 theories, respectively. N arXiv:1306.4320v3 [hep-th] 15 Jun 2015 CALT 68-2904 Contents 1. Introduction 1 2. 2d theories labeled by 4-manifolds 7 2.1 Kirby diagrams and plumbing 7 2.2 T [M4] as a boundary condition 12 2.3 Gluing along a common boundary 25 2.4 Cobordisms and domain walls 32 2.5 Adding a 2-handle 35 3. Top-down approach: fivebranes and instantons 40 3.1 Vafa-Witten theory 40 3.2 Gluing along 3-manifolds 44 3.3 Relation to affine Lie algebras 46 3.4 Cobordisms and gluing in the abelian case 48 3.5 Non-abelian generalizations 59 3.6 Linear plumbings and quiver structure 62 3.7 Handle slides 66 4.