DOCSLIB.ORG

Spaces of Incompressible Surfaces Allen Hatcher the Homotopy Type Of

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Spaces of Incompressible Surfaces Allen Hatcher the Homotopy Type Of Spaces of Incompressible Surfaces Allen Hatcher The homotopy type of the space of PL homeomorphisms of a Haken 3 manifold was computed in [H1], and with the subsequent proof of the Smale conjecture in [H2], the computation carried over to dieomorphisms as well. These results were also obtained independently by Ivanov [I1,I2]. The main step in the calculation in [H1], though not explicitly stated in these terms, was to show that the space of embeddings of an incom- pressible surface in a Haken 3 manifold has components which are contractible, except in a few special situations where the components have a very simple noncontractible homotopy type. The purpose of the present note is to give precise statements of these embedding results along with simplied proofs using ideas from [H3]. We also rederive the calculation of the homotopy type of the dieomorphism group of a Haken 3 manifold. Let M be an orientable compact connected irreducible 3-manifold, and let S be an incompressible surface in M , by which we mean: — S is a compact connected surface, not S2 , embedded in M properly, i.e., S ∩ ∂M = ∂S. — The normal bundle of S in M is trivial. Since M is orientable, this just means S is orientable. — The inclusion S,→M induces an injective homomorphism on 1 . We denote by E(S, M rel ∂S) the space of smooth embeddings S → M agreeing with the given inclusion S,→M on ∂S. The group Diff(S rel ∂S) of dieomorphisms S → S restricting to the identity on ∂S acts freely on E(S, M rel ∂S) by composition, with orbit space the space P (S, M rel ∂S) of subsurfaces of M dieomorphic to S by a dif- feomorphism restricting to the identity on ∂S. We think of points of P (S, M rel ∂S)as “positions” or “placements” of S in M . There is a bration Diff(S rel ∂S) → E ( S, M rel ∂S) → P ( S, M rel ∂S) giving rise to a long exact sequence of homotopy groups. It is known that iDiff(S rel ∂S) is zero for i>0, except when S is the torus T 2 and i = 1, when the inclusion T 2 ,→ 2 Diff(T ) as rotations induces an isomorphism on 1 . So the higher homotopy groups of E(S, M rel ∂S) and P (S, M rel ∂S) are virtually identical. 1 Theorem 1. Let S be an incompressible surface in M . Then: (a) iP (S, M rel ∂S)=0for all i>0unless ∂S = ∅ and S is the ber of a surface bundle structure on M . In this exceptional case the inclusion S1 ,→ P (S, M) as the ber surfaces induces an isomorphism on i for all i>0. (b) iE(S, M rel ∂S)=0for all i>0unless ∂S = ∅ and S is either a torus or the ber of a surface bundle structure on M . In these exceptional cases iE(S, M)=0 for all i>1. In the surface bundle case the inclusion of the subspace consisting of embeddings with image a ber induces an isomorphism on 1 . When S is a torus but not the ber of a surface bundle structure, the inclusion of the subspace consisting of embeddings with image equal to the given S induces an isomorphism on 1 . Here it is understood that iE(S, M rel ∂S) and iP (S, M rel ∂S) are to be com- puted at the basepoint which is the given inclusion S,→M. It is not hard to describe precisely what happens in the exceptional cases of (b). In the surface bundle case consider the exact sequence ∂ 0 → 1 Diff(S) → 1 E ( S, M) → 1 P ( S, M) → 0 Diff(S) By part (a) we have 1P (S, M) Z. The boundary map takes a generator of this Z to the monodromy dieomorphism dening the surface bundle. If this monodromy has innite order in 0Diff(S) then the boundary map is injective so 1E(S, M) 1Diff(S). If the monodromy has nite order in 0Diff(S), it is isotopic to a periodic dieomorphism of this order, as Nielsen showed. Hence M is Seifert-bered with coherently oriented bers, and there is an action of S1 on M rotating circle bers, and taking bers of the surface bundle structure to bers. The orbit of the given embedding of S under this action then generates a Z subgroup of 1E(S, M), which is all of 1E(S, M) unless S is a torus, in which case it is easy to see that 1E(S, M) Z Z Z. Using these results we can deduce: Theorem 2. If M is an orientable Haken manifold then iDiff(M rel ∂M)=0for all i>0unless M is a closed Seifert manifold with coherently orientable bers. In the latter case the inclusion S1 ,→ Diff(M) as rotations of the bers induces an isomorphism on i for all i>0, except when M is the 3 torus, in which case the circle of rotations S1 ,→ Diff(M) is replaced by the 3-torus of rotations M,→Diff(M). Proof: Suppose rst that ∂M =6 ∅, hence M is automatically Haken if it is irreducible. By the theory of Haken manifolds, there exists an incompressible surface S M with ∂S =6 ∅, in fact with ∂S representing a nonzero class in H1(∂M). Consider the bration Diff(M rel ∂M ∪ S) → Diff(M rel ∂M) → E ( S, M rel ∂S) 2 The ber can be identied with Diff(M0 rel ∂M0) where M 0 is the compact manifold, possibly disconnected, obtained by splitting M along S . If we know the theorem holds for M 0 , then from the long exact sequence of homotopy groups of the bration, together with part (b) of the preceding theorem, we deduce that the theorem holds for M . Again by Haken manifold theory, there is a nite sequence of such splitting operations reducing M to a disjoint union of balls. By the Smale conjecture the theorem holds for balls, so by induction the theorem holds for M . When M is a closed Haken manifold we again consider the bration displayed above, with S now a closed incompressible surface. If we are not in the exceptional cases that 1E(S, M) is nonzero, described in the paragraph before Theorem 2, the arguments in the preceding paragraph apply since M 0 is a nonclosed Haken manifold, for which the theorem has already been proved. There remain the cases that 1E(S, M) =0.6 (i)IfS is the ber of a surface bundle structure on M but not a torus, the result follows from the remarks preceding Theorem 2, describing how a generator of 1E(S, M) Z is represented by the orbit of the inclusion S,→M under the S1 action rotating bers of the Seifert bering. (ii)IfS is a torus but not the ber of a surface bundle, we have 1E(S, M) Z Z, the rotations of S . Under the boundary map 1E(S, M) → 0Diff(M rel S) each loop of rotations goes to a Dehn twist on one side of S and its inverse twist on the other side. The behavior of such twists in the mapping class group of the manifold M 0 is well known; see e.g. [HM]. In particular, the boundary map is injective unless M is orientably Seifert-bered with S a union of bers, in which case the kernel of the boundary map is Z represented by rotations of the circle bers. (iii)IfS is the torus ber of a surface bundle we have to consider the phenomena in both (i) and (ii). The monodromy dieomorphism of the torus ber dening the bundle is an element of SL2(Z). Note that a loop of rotations of S as in (ii) lies in the kernel of the boundary map i the rotations are in the direction of a curve in S xed by the monodromy. If the monodromy is trivial, M is the 3 torus and we have contributions to 1Diff(M) from both (i) and (ii), so we get M Diff(M) inducing an isomorphism on i for i>0. If the monodromy is nontrivial and of nite order, it has no real eigenvalues, so the boundary map in (ii) is injective and we get only the S1 Diff(M)asin(i). If the monodromy is of innite order and has 1 as an eigenvalue, it is a Dehn twist of the torus ber, so we get 1Diff(M) Z and this loop of dieomorphisms is realized by rotating bers of a bering of M by circles in the eigendirection in the torus bers of M . tu 3 Proof of Theorem 1. We will rst prove statement (b) when ∂S =6 ∅, which suces to deduce Theorem 2 in the nonclosed case. Then we will prove (a), and nally the remaining cases of (b). i Let ft : S → M , t ∈ D , be a family of embeddings representing an element of iE(S, M rel ∂S). We assume i>0, so all the surfaces ft(S) are isotopic rel ∂S to the given inclusion S,→M, hence are incompressible also. Let S I be a collar on one side of S = S {0} in M . By Sard’s theorem, ft(S) is transverse to S {x} for almost all x ∈ I . Transversality is preserved under small perturbations, so, since Di is compact, we i can choose a nite cover of D by open sets Uj such that ft(S) is transverse to a slice Sj = S {xj}SI for all t ∈ Uj .
Load more

Recommended publications
  • Commentary on Thurston's Work on Foliations
    COMMENTARY ON FOLIATIONS* Quoting Thurston's definition of foliation [F11]. \Given a large supply of some sort of fabric, what kinds of manifolds can be made from it, in a way that the patterns match up along the seams? This is a very general question, which has been studied by diverse means in differential topology and differential geometry. ... A foliation is a manifold made out of striped fabric - with infintely thin stripes, having no space between them. The complete stripes, or leaves, of the foliation are submanifolds; if the leaves have codimension k, the foliation is called a codimension k foliation. In order that a manifold admit a codimension- k foliation, it must have a plane field of dimension (n − k)." Such a foliation is called an (n − k)-dimensional foliation. The first definitive result in the subject, the so called Frobenius integrability theorem [Fr], concerns a necessary and sufficient condition for a plane field to be the tangent field of a foliation. See [Spi] Chapter 6 for a modern treatment. As Frobenius himself notes [Sa], a first proof was given by Deahna [De]. While this work was published in 1840, it took another hundred years before a geometric/topological theory of foliations was introduced. This was pioneered by Ehresmann and Reeb in a series of Comptes Rendus papers starting with [ER] that was quickly followed by Reeb's foundational 1948 thesis [Re1]. See Haefliger [Ha4] for a detailed account of developments in this period. Reeb [Re1] himself notes that the 1-dimensional theory had already undergone considerable development through the work of Poincare [P], Bendixson [Be], Kaplan [Ka] and others.
    [Show full text]
  • Arxiv:Math/0208110V1 [Math.GT] 14 Aug 2002 Disifiieymn Itntsraebnl Structures
    STRONGLY IRREDUCIBLE SURFACE AUTOMORPHISMS SAUL SCHLEIMER Abstract. A surface automorphism is strongly irreducible if every essential simple closed curve in the surface has nontrivial geomet- ric intersection with its image. We show that a three-manifold admits only finitely many inequivalent surface bundle structures with strongly irreducible monodromy. 1. Introduction A surface automorphism h : F F is strongly irreducible if every es- sential simple closed curve γ F→has nontrivial geometric intersection with its image, h(γ). This paper⊂ shows that a three-manifold admits only finitely many inequivalent surface bundle structures with strongly irreducible monodromy. This imposes a serious restriction; for exam- ple, any three-manifold which fibres over the circle and has b2(M) 2 admits infinitely many distinct surface bundle structures. ≥ The main step is an elementary proof that all weakly acylindrical sur- faces inside of an irreducible triangulated manifold are isotopic to fun- damental normal surfaces. As weakly acylindrical surfaces are a larger class than the acylindrical surfaces this strengthens a result of Hass [5]; an irreducible three-manifold contains only finitely many acylindrical surfaces. Section 2 gives necessary topological definitions, examples of strongly irreducible automorphisms, and precise statements of the theorems. arXiv:math/0208110v1 [math.GT] 14 Aug 2002 The required tools of normal surface theory are presented in Section 3. Section 4 defines weakly acylindrical and proves that every such sur- face is isotopic to a fundamental surface. In the spirit of the Georgia Topology Conference the paper ends by listing several open questions. Many of the ideas and terminology discussed come from the study of Heegaard splittings as in [2] and in my thesis [11].
    [Show full text]
  • Lecture Notes C Sarah Rasmussen, 2019
    Part III 3-manifolds Lecture Notes c Sarah Rasmussen, 2019 Contents Lecture 0 (not lectured): Preliminaries2 Lecture 1: Why not ≥ 5?9 Lecture 2: Why 3-manifolds? + Introduction to knots and embeddings 13 Lecture 3: Link diagrams and Alexander polynomial skein relations 17 Lecture 4: Handle decompositions from Morse critical points 20 Lecture 5: Handles as Cells; Morse functions from handle decompositions 24 Lecture 6: Handle-bodies and Heegaard diagrams 28 Lecture 7: Fundamental group presentations from Heegaard diagrams 36 Lecture 8: Alexander polynomials from fundamental groups 39 Lecture 9: Fox calculus 43 Lecture 10: Dehn presentations and Kauffman states 48 Lecture 11: Mapping tori and Mapping Class Groups 54 Lecture 12: Nielsen-Thurston classification for mapping class groups 58 Lecture 13: Dehn filling 61 Lecture 14: Dehn surgery 64 Lecture 15: 3-manifolds from Dehn surgery 68 Lecture 16: Seifert fibered spaces 72 Lecture 17: Hyperbolic manifolds 76 Lecture 18: Embedded surface representatives 80 Lecture 19: Incompressible and essential surfaces 83 Lecture 20: Connected sum 86 Lecture 21: JSJ decomposition and geometrization 89 Lecture 22: Turaev torsion and knot decompositions 92 Lecture 23: Foliations 96 Lecture 24. Taut Foliations 98 Errata: Catalogue of errors/changes/addenda 102 References 106 1 2 Lecture 0 (not lectured): Preliminaries 0. Notation and conventions. Notation. @X { (the manifold given by) the boundary of X, for X a manifold with boundary. th @iX { the i connected component of @X. ν(X) { a tubular (or collared) neighborhood of X in Y , for an embedding X ⊂ Y . ◦ ν(X) { the interior of ν(X). This notation is somewhat redundant, but emphasises openness.
    [Show full text]
  • Counting Essential Surfaces in 3-Manifolds
    Counting essential surfaces in 3-manifolds Nathan M. Dunfield, Stavros Garoufalidis, and J. Hyam Rubinstein Abstract. We consider the natural problem of counting isotopy classes of es- sential surfaces in 3-manifolds, focusing on closed essential surfaces in a broad class of hyperbolic 3-manifolds. Our main result is that the count of (possibly disconnected) essential surfaces in terms of their Euler characteristic always has a short generating function and hence has quasi-polynomial behavior. This gives remarkably concise formulae for the number of such surfaces, as well as detailed asymptotics. We give algorithms that allow us to compute these generating func- tions and the underlying surfaces, and apply these to almost 60,000 manifolds, providing a wealth of data about them. We use this data to explore the delicate question of counting only connected essential surfaces and propose some con- jectures. Our methods involve normal and almost normal surfaces, especially the work of Tollefson and Oertel, combined with techniques pioneered by Ehrhart for counting lattice points in polyhedra with rational vertices. We also introduce arXiv:2007.10053v1 [math.GT] 20 Jul 2020 a new way of testing if a normal surface in an ideal triangulation is essential that avoids cutting the manifold open along the surface; rather, we use almost normal surfaces in the original triangulation. Contents 1 Introduction3 1.2 Main results . .4 1.5 Motivation and broader context . .5 1.7 The key ideas behind Theorem 1.3......................6 2 1.8 Making Theorem 1.3 algorithmic . .8 1.9 Ideal triangulations and almost normal surfaces . .8 1.10 Computations and patterns .
    [Show full text]
  • Arxiv:2101.02945V3 [Math.GT] 15 Apr 2021
    On Crossing Ball Structure in Knot and Link Complements Wei Lin Abstract We develop a word mechanism applied in knot and link diagrams for the illustra- tion of a diagrammatic property. We also give a necessary condition for determining incompressible and pairwise incompressible surfaces, that are embedded in knot or link complements. Finally, we give a finiteness theorem and an upper bound on the Euler characteristic of such surfaces. 1 Introduction 1.1 Preliminary Discussion Let L ⊂ S3 be a link and π(L) ⊂ S2(⊂ S3) be a regular link projection. Additionally, let F ⊂ S3 − L be an closed incompressible surface. In 1981 Menasco introduced his crossing ball technology for classical link projections [7] that replaced π(L) in S2 with two 2-spheres, 2 2 2 3 2 2 S±, which had the salient features that L was embedded in S+ [ S− and S n (S+ [ S−) 3 2 was a collection of open 3-balls|B± that correspond to the boundaries S± and a collect of crossing balls. (Please see §1.2 for formal definition.) Using general position arguments, 2 2 this technology allows for placing F into normal position with respect to S± so that F \S± is a collection of simple closed curves (s.c.c.'s). When one imposes the assumption that π(L) is an alternating projection, the normal position of an essential surface is exceedingly well behaved to the point where by direct observation one can definitively state whether the link is split, prime, cabled or a satellite. As such, any alternating knot can by direct observation be placed into one of William Thurston's three categories|torus knot, satellite knot or hyperbolic knot [10].
    [Show full text]
  • Extension of Incompressible Surfaces on the Boundaries of 3-Manifolds
    PACIFIC JOURNAL OF MATHEMATICS Volume 194 (2000), pages 335{348 EXTENSION OF INCOMPRESSIBLE SURFACES ON THE BOUNDARIES OF 3-MANIFOLDS Michael Freedman1, Hugh Howards and Ying-Qing Wu2 An incompressible bounded surface F on the boundary of a compact, connected, orientable 3-manifold M is arc-extendible if there is a properly embedded arc γ on @M − IntF such that F [ N(γ) is incompressible, where N(γ) is a regular neighbor- hood of γ in @M. Suppose for simplicity that M is irreducible and F has no disk components. If M is a product F × I, or if @M − F is a set of annuli, then clearly F is not arc-extendible. The main theorem of this paper shows that these are the only obstructions for F to be arc-extendible. Suppose F is a compact incompressible surface on the boundary of a compact, connected, orientable, irreducible 3-manifold M. Let F 0 be a component of @M − IntF with @F 0 6= ;. We say that F is arc-extendible (in F 0) if there is a properly embedded arc γ in F 0 such that F [ N(γ) is incompressible. In this case γ is called an extension arc of F . We study the problem of which incompressible surfaces on the boundary M are arc-extendible. The result will be used in [H], in which it is shown that a compact, orientable 3-manifold M contains arbitrarily many disjoint, non-parallel, non-boundary parallel, incompressible surfaces, if and only if M has at least one boundary component of genus greater than or equal to two.
    [Show full text]
  • Some Definitions: If F Is an Orientable Surface in Orientable 3-Manifold M
    Some definitions: If F is an orientable surface in orientable 3-manifold M, then F has a collar neighborhood F × I ⊂ M. F has two sides. Can push F (or portion of F ) in one direction. M is prime if every separating sphere bounds a ball. M is irreducible if every sphere bounds a ball. M irreducible iff M prime or M =∼ S2 × S1. A disjoint union of 2-spheres, S, is independent if no compo- nent of M − S is homeomorphic to a punctured sphere (S3 - disjoint union of balls). F is properly embedded in M if F ∩ ∂M = ∂F . Two surfaces F1 and F2 are parallel in M if they are disjoint and M −(F1 ∪F2) has a component X of the form X = F1 ×I and ∂X = F1 ∪ F2. A compressing disk for surface F in M 3 is a disk D ⊂ M such that D ∩ F = ∂D and ∂D does not bound a disk in F (∂D is essential in F ). Defn: A surface F 2 ⊂ M 3 without S2 or D2 components is incompressible if for each disk D ⊂ M with D ∩ F = ∂D, there exists a disk D0 ⊂ F with ∂D = ∂D0 1 Defn: A ∂ compressing disk for surface F in M 3 is a disk D ⊂ M such that ∂D = α ∪ β, α = D ∩ F , β = D ∩ ∂M and α is essential in F (i.e., α is not parallel to ∂F or equivalently 6 ∃γ ⊂ ∂F such that α ∪ γ = ∂D0 for some disk D0 ⊂ F . Defn: If F has a ∂ compressing disk, then F is ∂ compress- ible.
    [Show full text]
  • Arxiv:1905.11637V5 [Math.GT] 28 Dec 2020 Hr Γi H Lsiyn Pc Ftegopγ Iegy,W Assum We Top Ghys, Discrete Like the Γ
    DYNAMICAL AND COHOMOLOGICAL OBSTRUCTIONS TO EXTENDING GROUP ACTIONS KATHRYN MANN AND SAM NARIMAN Abstract. Motivated by a question of Ghys, we study obstructions to ex- tending group actions on the boundary ∂M of a 3-manifold to a C0-action on M. Among other results, we show that for a 3-manifold M, the S1 × S1 action on the boundary does not extend to a C0-action of S1 × S1 as a discrete group on M, except in the trivial case M ≅ D2 × S1. 1. Introduction This paper concerns the structure of diffeomorphism and homeomorphism groups of manifolds. Our motivation is the following seemingly simple question of Ghys. Question 1.1 ([Ghy91]). If M is a manifold with boundary ∂M, under what ∞ conditions is there a homomorphism Diff 0(∂M) → Diff 0(M) that “extends C - diffeomorphisms to the interior”? Here and in what follows, Diff(M) denotes the group of self-diffeomorphisms of M, and Diff0(M) its identity component. Put otherwise, Ghys’ question asks for obstructions to a group-theoretic section of the natural “restriction to boundary” map r∶ Diff 0(M) → Diff0(∂M). Restricting the domain of the map to Diff0(M) ensures that the boundary map is surjective onto Diff0(∂M), thus any such ob- struction will necessarily be group-theoretic in nature. Ghys’ original work treats the case where M is an n-dimensional ball (for general n), a case explored further in [Man13]. This program is also reminiscent of Browder’s notion of bordism of diffeomorphisms, as discussed at the end of this section.
    [Show full text]
  • Incompressible Surfaces, Hyperbolic Volume, Heegaard Genus and Homology Marc Culler, Jason Deblois and Peter B
    communications in analysis and geometry Volume 17, Number 2, 155–184, 2009 Incompressible surfaces, hyperbolic volume, Heegaard genus and homology Marc Culler, Jason Deblois and Peter B. Shalen We show that if M is a complete, finite-volume, hyperbolic Z ≥ 3-manifold having exactly one cusp, and if dimZ2 H1(M; 2) 6, then M has volume greater than 5.06. We also show that if M is Z ≥ a closed, orientable hyperbolic 3-manifold with dimZ2 H1(M; 2) 1 4, and if the image of the cup product map H (M; Z2) ⊗ 1 2 H (M; Z2) → H (M; Z2) has dimension at most 1, then M has volume greater than 3.08. The proofs of these geometric results involve new topological results relating the Heegaard genus of a closed Haken manifold M to the Euler characteristic of the kishkes of the complement of an incompressible surface in M. 1. Introduction If S is a properly embedded surface in a compact 3-manifold M, let M \\ S denote the manifold that is obtained by cutting along S; it is homeomorphic to the complement in M of an open regular neighborhood of S. The topological theme of this paper is that the bounded manifold ob- tained by cutting a topologically complex closed simple Haken 3-manifold along a suitably chosen incompressible surface S ⊂ M will also be topolog- ically complex. Here the “complexity” of M is measured by its Heegaard genus, and the “complexity” of M \\ S is measured by the absolute value of the Euler characteristic of its “kishkes” (see Definitions 1.1 below).
    [Show full text]
  • Incompressible Surfaces in Handlebodies and Closed 3-Manifolds of Heegaard Genus 2
    PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 128, Number 10, Pages 3091{3097 S 0002-9939(00)05360-0 Article electronically published on May 2, 2000 INCOMPRESSIBLE SURFACES IN HANDLEBODIES AND CLOSED 3-MANIFOLDS OF HEEGAARD GENUS 2 RUIFENG QIU (Communicated by Ronald A. Fintushel) Abstract. In this paper, we shall prove that for any integer n>0, 1) a handlebody of genus 2 contains a separating incompressible surface of genus n, 2) there exists a closed 3-manifold of Heegaard genus 2 which contains a separating incompressible surface of genus n. 1. Introduction Let M be a 3-manifold, and let F be a properly embedded surface in M. F is said to be compressible if either F is a 2-sphere and F bounds a 3-cell in M,or there exists a disk D ⊂ M such that D \ F = @D,and@D is nontrivial on F . Otherwise F is said to be incompressible. W. Jaco (see [3]) has proved that a handlebody of genus 2 contains a nonsep- arating incompressible surface of arbitrarily high genus, and asked the following question. Question A. Does a handlebody of genus 2 contain a separating incompressible surface of arbitrarily high genus? In the second section, we shall give an affirmative answer to this question. The main result is the following. Theorem 2.7. A handlebody of genus 2 contains a separating incompressible sur- face S of arbitrarily high genus such that j@Sj =1. If M is a closed 3-manifold of Heegaard genus 1, then M is homeomorphic to either a lens space or S2 ×S1.
    [Show full text]
  • Essential Surfaces in Amalgamated 3-Manifolds
    ESSENTIAL SURFACES IN AMALGAMATED 3-MANIFOLDS DAVID BACHMAN AND SAUL SCHLEIMER Abstract. Let Mφ denote the 3-manifold obtain by identifying the boundaries of two small hyperbolic 3-manifolds by the homeomorphism φ. The genus of any essential surface, other than the amalgamating surface, in Mφ is forced to be arbi- trarily high by making the map φ sufficiently complicated. Keywords: Incompressible Surface 1. Introduction In his thesis K. Hartshorn show that when a map identifying the boundaries of two handlebodies is complicated then the genus of any essential surface in the resulting 3-manifold must be high [Har02]. Here we consider what happens when gluing two small, hyperbolic 3-manifolds along their boundaries. Of course, we have no control over the genus of the amalgamating surface. But we do show that when the gluing map is complicated then the genus of any other essential surface must be high. Our first task is to define the complexity of the map used to glue two 3-manifolds together. Following Hempel [Hem01], we will make use of the curve complex to do this. Let F be a 2-manifold. It’s curve complex is defined by the following relations: • vertices ↔ isotopy classes of essential loops on F . • n-simplices ↔ sets of n non-isotopic essential loops which can be isotoped to be pairwise-disjoint. Note that the path metric on the 1-skeleton of the curve complex gives a well-defined, integer-valued metric on the 0-skeleton. Let X and Y be 3-manifolds with homeomorphic boundaries. Fix triangulations ∆X and ∆Y of X and Y .
    [Show full text]
  • Notes on 3-Manifolds
    CHAPTER 1: COMBINATORIAL FOUNDATIONS DANNY CALEGARI Abstract. These are notes on 3-manifolds, with an emphasis on the combinatorial theory of immersed and embedded surfaces, which are being transformed to Chapter 1 of a book on 3-Manifolds. These notes follow a course given at the University of Chicago in Winter 2014. Contents 1. Dehn’s Lemma and the Loop Theorem1 2. Stallings’ theorem on ends, and the Sphere Theorem7 3. Prime and free decompositions, and the Scott Core Theorem 11 4. Haken manifolds 28 5. The Torus Theorem and the JSJ decomposition 39 6. Acknowledgments 45 References 45 1. Dehn’s Lemma and the Loop Theorem The purpose of this section is to give proofs of the following theorem and its corollary: Theorem 1.1 (Loop Theorem). Let M be a 3-manifold, and B a compact surface contained in @M. Suppose that N is a normal subgroup of π1(B), and suppose that N does not contain 2 1 the kernel of π1(B) ! π1(M). Then there is an embedding f :(D ;S ) ! (M; B) such 1 that f : S ! B represents a conjugacy class in π1(B) which is not in N. Corollary 1.2 (Dehn’s Lemma). Let M be a 3-manifold, and let f :(D; S1) ! (M; @M) be an embedding on some collar neighborhood A of @D. Then there is an embedding f 0 : D ! M such that f 0 and f agree on A. Proof. Take B to be a collar neighborhood in @M of f(@D), and take N to be the trivial 0 1 subgroup of π1(B).
    [Show full text]