Questions tagged [gt.geometric-topology]
Topology of cell complexes and manifolds, classification of manifolds (e.g. smoothing, surgery), low dimensional topology (e.g. knot theory, invariants of 4-manifolds), embedding theory, combinatorial and PL topology, geometric group theory, infinite dimensional topology (e.g. Hilbert cube manifolds, theory of retracts).
4,129
questions
10
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1
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441
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An incomplete characterisation of the Euclidean line?
We say that a metric space $(X, d)$ is a Banakh space if for every $\rho \in \mathbb{R}_{> 0}$ and every $x \in X$, there are
$a,b \in X$ such that $\{y \in X \, \vert \, d(x, y) = \rho\} = \{a, b\}...
6
votes
2
answers
602
views
Powers of meridians in knot groups
Given a (tame) knot $K \subset S^3$, let $t \in G = \pi_1(S^3 - K)$ be any meridian. The Wirtinger presentation shows that $\langle \langle t \rangle \rangle = G$, where the notation indicates the ...
2
votes
0
answers
114
views
Foliation of $X$ by once punctured planes without any singularities
Let $n=3.$
Take $X=(0,1)^n.$ Fix points $p,q$ s.t. $\text{dist}_n(p,q)=\sqrt{n}.$ Construct a smooth regular foliation of $X$ with $(n-1)-$dim. leaves which are topologically $(0,\sqrt{n})\times S^{n-...
8
votes
2
answers
330
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Is every contractible homogeneous space of a connected Lie group homeomorphic to a Euclidean space?
Problem. Let $G$ be a connected Lie group and $H$ is a closed subgroup of $G$ such that the homogeneous space $G/H$ is contractible. Is $G/H$ homeomorphic to a Euclidean space $\mathbb R^n$ for some $...
4
votes
0
answers
180
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Symmetric line spaces are homeomorphic to Euclidean spaces
For points $x,y,z$ of a metric space $(X,d)$ we write $\mathbf Mxyz$ and say that $y$ is a midpoint between $x$ and $z$ if $d(x,z)=d(x,y)+d(y,z)$ and $d(x,y)=d(y,z)$.
Definition: A metric space $(X,d)$...
3
votes
0
answers
93
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Using blow-up for handle attachment
In basic surgery theory, it is clear what happens topologically when one "adds a handle", but getting the smooth structure right requires care. For example, in identifying opposite sides of ...
3
votes
0
answers
131
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Isotopy-classes of oriented Schoenflies spheres in $S^4$ is a group under oriented connect-sum
Given two oriented, smoothly-embedded copies of $S^3$ in $S^4$ (called Schoenflies spheres), one can take an oriented connect-sum of the pairs $(S^4, M_1) \# (S^4, M_2)$. This puts a monoidal ...
13
votes
1
answer
431
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Compact closed aspherical manifolds with vanishing second homology in all the covering spaces
I wonder if there exists a compact closed smooth aspherical manifold $M$ of dimension at least $4$, so that for any covering space $\tilde{M}$ over $M,$ we always have $H_2(\tilde{M},\mathbb{Z})=0$ ...
4
votes
2
answers
422
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Finite application of one of Reidemeister moves on a knot diagram
It is known that given a knot diagram we can transform it into a trivial unknot diagram by a series of Reidemeister moves. The key word is "series".
Can we transform any knot diagram using a ...
4
votes
1
answer
136
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Topological type of complement of Heegaard curves in Heegaard surface $(\Sigma - \alpha - \beta)$
Suppose $(\Sigma, \alpha, \beta)$ is a genus-$g$ Heegaard diagram for a closed, oriented $3$-manifold $Y$, i.e. $\Sigma$ is an orientable genus-$g$ surface, and $(\alpha_1, \dots, \alpha_g)$ and $(\...
7
votes
1
answer
221
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Hyperbolic homology spheres with infinite $\mathrm{SL}_2(\mathbb{C})$ character variety
$\DeclareMathOperator\SL{SL}$By the celebrated results of Culler and Shalen, a closed $3$-manifold contains an incompressible surface if its $\SL_2(\mathbb{C})$ character variety is infinite.
Now, for ...
47
votes
3
answers
3k
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A metric characterization of the real line
Is the following metric characterization of the real line true (and known)?
A nonempty complete metric space $(X,d)$ is isometric to the real line if and only if for every $c\in X$ and positive real ...
14
votes
2
answers
444
views
Identify this 16 crossing knot
For this knot with DT code
-8 16 28 14 -2 6 -20 10 24 -32 -12 -30 18 -22 4 -26
I received an error message from Knot Finder:
"KnotFinder encountered an unknown error."
I also tried SnapPy (...
2
votes
1
answer
215
views
How to get a presentation of the mapping class group of the $n$-punctured sphere
$\DeclareMathOperator\Mod{Mod}$I would like to compute the mapping class group (homeomorphism preserving orientation modulo those isotopic to the identity) of the sphere $S^2$ minus $n$ points $p_1,\...
7
votes
1
answer
268
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Dupin cyclide as the stereographic projection of a Hopf torus
Let $H \colon S^3 \to S^2$ be the Hopf map and let $\gamma$ be a curve on $S^2$. Then $H^{-1}(\gamma)$ is called the Hopf cylinder or the Hopf torus when $\gamma$ is closed, with profile curve $\gamma$...
5
votes
3
answers
530
views
If a polyhedron in $\mathbb{R}^3$ has local intersections, does it also have more global intersections?
Consider a simplicial complex $K$. A piecewise linear map $f: K \to \mathbb{R}^n$ is an almost-embedding if $f(\sigma) \cap f(\tau) = \emptyset$ for any two disjoint simplices $\sigma,\tau$ in $K$.
...
4
votes
1
answer
119
views
Inheritance of arithmeticity properties in orbifold strata
Suppose $M = K\backslash G/\Gamma$ is a quotient of a symmetric space by a lattice. I don't know all of the proper adjectives to apply here (e.g. what should be said about $G$ and so on), but I wouldn'...
4
votes
0
answers
162
views
Every closed surface divides a closed 3-manifold $X$ into two parts if and only if $H_1(X)$ is finite
My friend is looking for proof of the following statement
Every closed surface divides a closed 3-manifold $X$ into two parts if and only if $H_1(X; \mathbb{Z})$ is finite.
Rumor source: Justin ...
3
votes
0
answers
70
views
non-negative curvature condition for polyhedral manifolds
A polyhedral manifold P, i.e, a topological manifold with a triangulation where each simplex is isometric to a simplex in Euclidean space (other constant curvature spaces are allowed), is said to have ...
3
votes
0
answers
99
views
Explicit parameterizations of complicated unlinks?
I have a somewhat empirical question which I hope is still welcome here. I would like to know how to write down explicit parameterizations of "complicated unlinks", say with 2 or 10 ...
14
votes
1
answer
565
views
How do we know there are no more Deligne–Mostow/Thurston lattices?
In the context of hypergeometric functions, Deligne and Mostow enumerated several lattices in complex hyperbolic space/the rank 1 Lie group $\operatorname{PU}(1,n)$ (see [1] and [2]). Thurston used ...
2
votes
0
answers
67
views
Maximal orders and surface subgroups of even genus
Let $A$ be a quaternion algebra over a totally real number field $k$. Suppose that $A$ splits at exactly one real place of $A$. Let $\mathcal{O}$ be a maximal order in $A$. Then $\mathcal{O}$ contains ...
5
votes
1
answer
223
views
Amenable link groups
The unknot and the Hopf link are (as far as I know) the only links whose complements have abelian fundamental groups. Are there more examples whose complement have amenable fundamental group?
2
votes
1
answer
184
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What is known about the almost complex structure on the Teichmüller space in Fenchel–Nielsen coordinates?
There has been a question on the same subject, but I'm asking about something more specific.
In the Fenchel–Nielsen coordinates, the Teichmüller space of genus $g$ is represented as $\mathbb{R}^{3g-3}\...
5
votes
2
answers
335
views
Does every triangulable manifold have a vertex-transitive triangulation?
Does every triangulable manifold have a vertex-transitive triangulation?
When I talk about a vertex-transitive triangulation of a manifold, I mean in the sense of realizing a manifold homeomorphically ...
2
votes
1
answer
191
views
Corollary in Rasmussen's paper about $s$-grading of Lee's canonical generators
In Jacob Rasmussen's paper Khovanov homology and the slice genus, he states as Corollary 3.6 that $s(\mathfrak s_o)=s(\mathfrak s_{\bar o})=s_{min}(K)$, where $s$ is the $s$-grading and $\mathfrak s_o,...
4
votes
1
answer
145
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Existence of tubular neighborhood of singular complex subvariety
Let $X$ be a smooth complex projective manifold and let $Y$ be a closed subvariety of $X$ with $y\in Y$ a fixed point. Does there exist an open neighborhood $U$ of $Y$ such that $\pi_1(Y,y)\to \pi_1(U,...
3
votes
1
answer
206
views
Handle attachment information from Morse function and triangulation
First, allow me to setup the relevant information. It is well known that a Morse function $f:M\to\mathbb{R}$ induces a handle decomposition of $M$.
For simplicity, let's restrict for now to the ...
7
votes
1
answer
175
views
Calculating the Seifert framing for an exceptional fiber in a Seifert-fibered integer homology 3-sphere
Let $Y=\Sigma(\alpha_{1},\dots,\alpha_{n})$ be a Seifert fibered homology 3-sphere, let $\pi:Y\to\Sigma$ denote the projection to the orbifold surface, and let $T\subset Y$ be the pre-image under $\pi$...
4
votes
1
answer
222
views
Bounds for the crossing number in terms of the braid index?
Is there a lower bound on the crossing number of a knot (resp., link) with braid index $b$?
For knots, I believe the smallest crossing number for braid index 2 is 3, the smallest crossing number for ...
3
votes
1
answer
186
views
Maps of surfaces to CAT(0) cube complexes
Let $C$ be a locally CAT(0) cube complex. Let $f\colon \Sigma_g \rightarrow C$ be a continuous map from a closed oriented genus $g \geq 1$ surface to $C$. Is it always possible to find a cube ...
3
votes
1
answer
306
views
Simplified Bing's house
Bing's house is an example of contractible 2-complex in $\mathbb{R}^3$.
One may think that it is a surface without boundary that has two types of singularities: tripod curves — curves where three ...
10
votes
0
answers
197
views
Bi-Lipschitz mappings
Assume that we have a bi-Lipschitz mapping $f:\bar{\mathbb{B}}^n(0,1)\to\mathbb{R}^n$. The mapping need not be smooth anywhere and it may happen that it cannot be extended to a homeomorphism of a ...
3
votes
1
answer
345
views
Boundaries of subsets of simply-connected domains
I am trying to prove the following assertion: Let $B$ be a simply-connected set, and let $B' \subsetneq B$ be a proper open connected subset. Then, there exists a point $x \in \partial B'$ of the ...
3
votes
0
answers
67
views
Discreteness of volumes of boundary-parabolic representations
Suppose $M$ is a cusped hyperbolic $3$-manifold of finite volume. Let $\mathfrak{R}_0(M)$ be the space of boundary-parabolic representations $\rho : \pi_1(M) \to \operatorname{PSL}_2(\mathbb C)$. Is ...
11
votes
0
answers
224
views
The second coefficient of the Conway polynomial from Knot Floer homology
Let $\nabla_K(z)$ be the Conway polynomial and $\Delta_K(t)$ be the Alexander polynomial normalized by $\Delta_K(t)=\Delta_K(t^{-1})$ and $\Delta_K(1)=1$,
These invariants are equivalent and they are ...
7
votes
2
answers
254
views
Surjections from genus $n$ surface group to free group of rank $n$
Let $\Sigma_n$ be a genus $n$ surface, let $\mathcal{H}_n$ be a genus $n$ handle body, and let $F_n$ be a free group of rank $n$. Fix an identification of $\pi_1(\mathcal{H}_n)$ with $F_n$. I know ...
12
votes
1
answer
577
views
Definition of Thurston's skinning map
A key construction in Thurston's proof of the existence of hyperbolic structures on Haken manifolds is the so-called "skinning map" associated to a 3-manifold $M$ with boundary whose ...
6
votes
1
answer
297
views
"Neck cutting" and why gauge theory doesn't work on homotopy 4-spheres
I attended a talk recently and the speaker said, essentially, that gauge theory invariants are expected to never be able to detect exotic 4-spheres because they always vanish, for a reason related to ...
6
votes
2
answers
165
views
Generate $\mathrm{Mod}(S_g)$ by two Dehn twists
Let $S_g$ be a closed orientable surface of genus $g>1$.
How can one prove that its mapping class group $\mathrm{Mod}(S_g)$
is not generated by two Dehn twists?
A pair of simple closed curves in $...
0
votes
0
answers
86
views
Terminology for discrete subgroups of PSL(2,k), where k is a non-archimedean local field
$\DeclareMathOperator\PSL{PSL}$I'm asking about terminology for discrete subgroups of $\PSL(2,k)$, where $k$ is a non-archimedean local field.
As it is rather clumsy to have to use such expressions ...
1
vote
0
answers
106
views
Instantons on the 4-sphere with respect to other Riemannian metrics
It is known that the moduli space of $\text{SU}(2)$ instantons of charge $1$ on $S^4$ is diffeomorphic to the five-ball $B^5$ if $S^4$ is endowed with the round metric.
Question: what does the moduli ...
5
votes
0
answers
119
views
Can every homeomorphism of the 4-ball fixing the boundary be approximated by diffeomorphisms smoothly isotopic to the identity?
Let $B^{n}$ denote the euclidean closed ball of dimension $n$. Alexander's trick shows that every homeomorphism of $B^{n}$ fixing $\partial B^n$ is $C^{0}$-isotopic to the identity via a boundary ...
0
votes
0
answers
73
views
Is there any functoriality of Stallings' twists?
Suppose $L$ is an oriented link and $L'$ is a link obtained from the Stallings' twists.
Are there any functoriality of the twist operation on the links, such as functoriality between (1) homology ...
3
votes
0
answers
106
views
Finite homology of a homogeneous space
Let $\Gamma$ be a cocompact lattice in $\operatorname{SL}(2,\mathbb R)$ and $X=\operatorname{SL}(2,\mathbb R)/\Gamma$ be the underlying homogeneous space. Can the homology group $H_1(X,\mathbb Z)$ be ...
5
votes
0
answers
88
views
Irreducible factors of the A-polynomial
The A-polynomial $A_K$ of a knot $K$ describes the irreducible "non-abelian" components of the $SL(2)$-character variety of $S^3-K.$
Does anyone know a knot K for which $A_K$ has more ...
3
votes
0
answers
283
views
Fundamental group of blow-ups
Let $M$ be a simply-connected compact complex manifold of dimension three and $C$ is a smooth complex curve in $M$.
Let $M'$ be the blow-up of $M$ along $C$.
My question is:
Is $M'$ also simply-...
3
votes
1
answer
175
views
Squier's conjecture on Burau at roots of unity
In Squier's short, yet influential, paper about the Burau representation, he made two conjectures that might have provided a proof for the faithfulness of the Burau representation (which we now know ...
3
votes
1
answer
210
views
Example of a non $\pi_1$-injective, degree one, self-map of a three-manifold
All manifolds will be assumed to be closed, oriented, and connected.
Let $f\colon M\to M$ be a map of degree $\pm 1$. It is not hard to show that $\pi_1(f)$ is surjective.
What is an example of a non ...
4
votes
0
answers
259
views
Does this "join-like complex" of $K_5$ and $K_3$ embed in $\Bbb R^4$?
Consider the following 2-dimensional CW-complex: its 1-skeleton is $K_8$, which we write as an edge-disjoint union $K_5\cup K_{5,3}\cup K_3$.
Then for any two edges $ab\in E(K_5)$ and $cd\in E(K_3)$ ...