All Questions
Tagged with gt.geometric-topology at.algebraic-topology
1,145 questions
3
votes
1
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266
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Poincaré dual of the generators of $H^d(\mathbb{RP}^5,\mathbb{Z}_2)$
We know $H^d(\mathbb{RP}^5,\mathbb{Z}_2)=\mathbb{Z}_2$. So there are two classes of $\mathbb{Z}_2$ generators, trivial and nontrivial, for $d=0,1,2,3,4,5$.
Wha are the Poincaré dual $(5-d)$-...
- 10.5k
3
votes
1
answer
158
views
Cyclic polytopes whose boundary is a flag complex
A cyclic polytope $C(n, d)$ is defined as the convex hull of $n$ distinct points on the moment curve in $\mathbb{R}^d$ (here $n>d$). This is a simplicial polytope so its boundary $\partial C(n, d)$ ...
- 1,017
3
votes
1
answer
463
views
cohomology module of unit tangent vector bundles over spheres
Let $S^m$ be the $m$-sphere and $\tau (S^m)$ the sphere bundle consisting of unit tangent vectors in the tangent bundle $TS^m$. Then we have a fibration
$$
S^{m-1}\longrightarrow \tau(S^m)\...
- 2,223
3
votes
1
answer
335
views
"Ambient homotopy" between preimages under a fiber bundle?
Choose a notion of an "ambient homotopy" between maps of topological spaces. For example, say that two embeddings $Y \rightarrow X$ are ambiently homotopic if there is a path between them in the space ...
- 2,312
3
votes
1
answer
453
views
geometric conditions on maps between manifolds inducing monomorphisms on cohomology
Let $M,N$ be manifolds whose dimensions may be different. Let $f: M\longrightarrow N$ be a smooth map. What geometric conditions on $f$ can we impose such that the induced homomorphism
$$
f^*: H^*(N;\...
- 2,223
3
votes
1
answer
123
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Involution on the set of isomorphism classes of 2n-dimensional vector bundles induced by an involution of $O(2n)$
Denote by $\varphi$ the automorphism of $O(2n)$ given by $\varphi (A)=det(A)\cdot A$.This induces a self-map $B\varphi$ of $BO(n)$, so it induces a self-map (actually an involution)
$B\varphi ^*$ on $[...
- 3,051
3
votes
1
answer
909
views
Isomorphism between a mapping class group and the fundamental group of a moduli space
For some fixed integer $d \geq 3$, let $M(0, d)$ be the mapping class group of self-homeomorphisms of the Riemann sphere which fix each of the $d$ points $0, 1, ... , d-2, \infty$. Let $X$ be the ...
- 1,298
3
votes
1
answer
99
views
cartesian product rigidity for the punctured open disc
Q1: Let $D^n$ ($n\geq 1$) be the n-dimensional open disk. If $D^n-\{0\}$ is homeomorphic to $X\times (0,1)$, for some topological space $X$, does it necessarily follow that $X$ is homeomorphic to $S^{...
- 7,609
3
votes
1
answer
470
views
Spectral sequence for H-space bundles
Let $F \rightarrow E \rightarrow B$ be a fibre bundle such that $B$ is a smooth and compact manifold and $F$ obtains an associative H-space structure. Explicitly, it is not a principal bundle.
One ...
- 31
3
votes
1
answer
806
views
a CW-complex homotopic to a manifold
I'm reading a paper and here the authors say that a connected 4-manifold with zero rational top homology has a homotopy type of 3-dimensional CW-structure. I can't figure out how it can be done.
- 537
3
votes
1
answer
171
views
Spaces satisfying a strong Cartan-Hadamard theorem
Let $(X,d)$ be a connected geodesic metric space. When does there there exists a covering map $\pi:H\rightarrow X$ which is a local-isometry where $H$ is either a Hilbert space or a Euclidean space?
...
- 364
3
votes
1
answer
257
views
Deformation equivalent Hodge structures
An HH type is the oriented homotopy type of a closed simply-connected Kähler manifold together with the Hodge structure on cohomology.
Two HH types are deformation equivalent if they are represented ...
user164740
3
votes
1
answer
245
views
Wall self-intersection invariant for odd-dimensional manifolds?
I am trying to convince myself that a naïve definition of the Wall self intersection number should not work for odd-dimensional manifolds. Namely, let $X^{2n-1}$ be a smooth oriented closed manifold ...
- 5,349
3
votes
1
answer
135
views
Submanifold generator of Pontryagin-dual of the torsion subgroup of the $Pin^+$ bordism group (dimension 4th)
I am interested in figuring out the following submanifold generator of a $Pin^+$ Bordism or Cobordism group in the dimension 4, say for a $Pin^+$ cobordism group of the classifying space $BG=BSU(2)$:
...
- 2,147
3
votes
1
answer
115
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Decomposing global isotopies into local ones
I'm looking for a reference for the following basic-looking statement:
Let $X$ be a smooth manifold covered by open sets $U_1$ and $U_2$. Let $f:X \rightarrow X$ be a map isotopic to identity via an ...
- 3,772
3
votes
1
answer
580
views
Can lens spaces be realized by surgery along torus links?
As we know, the Lens space $L(p,q)$ is the quotient of $S^3$ by a $\mathbb{Z}_p$ action:
$(z_1,z_2) \rightarrow (e^{2\pi i/p}z_1,e^{2\pi iq/p}z_2)$.
It seems that the Lens space $L(1,0)$, a.k.a $S^3$,...
- 143
3
votes
1
answer
180
views
cohomology ring of infinite iterated loop space
What is the cohomology ring
$$
H^*(\Omega^\infty \Sigma^\infty (S^m\vee S^n);\mathbb{Z}_2)?
$$
I already write out the graded-vector-space basis using Dyer-Lashof operations, but I do not know how to ...
- 2,223
3
votes
1
answer
319
views
Fixed point property for intersection of spaces which are homeomorphic to a disk
The following question is question 9.8 from Miller's paper ``Some interesting problems
'':
Question Suppose $D_n$ a subset of the plane is homeomorphic to a disk and for every
$n\in \omega, D_{n+...
- 32.2k
3
votes
1
answer
459
views
When is the Freudenthal compactification an ANR?
Let $X$ be a locally compact metric ANR (or, if preferred, a locally compact simplicial complex). If needed, assume that $X$ has finitely many ends or is of finite dimension. My question is:
What are ...
- 2,104
3
votes
2
answers
486
views
Poset fiber theorems under a special assumption on the poset map?!
Hey everyone, I am facing the following problem:
Say that a (order-preserving) poset map $f:P\to Q$ has property $(\star)$ if for all $q_1,q_2\in Q$ with $q_1\leq q_2$ and every $p_2\in f^{-1}(q_2)$ ...
- 937
3
votes
1
answer
143
views
Two paths to the boundary with no holes in between
Let $X\subset \mathbb{R}^2$ be open connected (and let's say bounded), let $x\in X$ and $y\in\partial X$ be such that there is a Jordan curve $\gamma:[0,1]\to X\cup\{y\}$ such that $\gamma(0)=x$ and $\...
- 5,529
3
votes
1
answer
224
views
Homology modules and symmetry
Let $B$ be a cellular (simplicial, semi-simplicial etc) complex having $\mathbb{Z}^n$-symmetry (that is, there is a free action of $\mathbb{Z}^n$ on $B$, commuting with the boundary operators) and let ...
- 93
3
votes
1
answer
403
views
Geometry of the second barycentric subdivision (and Thomason-fibrant replacement)
Is
$\mathrm{sd}^2 (\Delta^n) = \mathrm{sd}^2(\partial \Delta^n) \times \Delta^1 \cup_{\mathrm{sd}^2(\partial \Delta^n) \times \{1\}} Cone(\mathrm{sd}^2(\partial \Delta^n))$
? Here $\mathrm{sd}^2$ ...
- 64k
3
votes
1
answer
323
views
self-Whitney sum of the canonical vector bundle on Grassmannians
Let $G_{k}(\mathbb{R}^N)$ be the Grassmannian manifold consisting of $k$-subspaces in $\mathbb{R}^N$. There is a canonical $k$-dimensional vector bundle
$$
\gamma_{k,N}: \mathbb{R}^k\longrightarrow E(...
- 1,990
3
votes
1
answer
366
views
cohomology ring of configuration spaces
In the paper configuration spaces: applications to Gelfand-Fuks cohomology, by F. Cohen and L. Taylor, Bull. Amer. Math. Soc., 1978, theorem 1, I did not find the proof. What method did the author use ...
- 1,990
3
votes
1
answer
293
views
Transfinite sequence of contiguous simplicial maps
Recall that two simplicial maps of (abstract) simplicial complexes $f,g\colon K\to L$ are contiguous if $f(\sigma)\cup g(\sigma)$ is a simplex of $L$ for every simplex $\sigma\in K$. Contiguous ...
- 2,104
3
votes
1
answer
265
views
Equivariant Surgery problem
I have a question about surgery.
Let $G= \mathbb{Z}_m \times \mathbb{Z}$ and $M$ be a oriented 3-manifold with G-action. i.e. There exists a map $f\colon M/G \to BG$, where $BG$ is classifying space.(...
- 698
3
votes
1
answer
4k
views
How to show that the "bing's house with two rooms" is contractible? [closed]
I can't image this, Someone can give a clear illustration?
- 187
3
votes
1
answer
173
views
Parameterizing the space of convex quadrilaterals
If $P=\mathbb{R}^2$ is the plane, is there a continuous surjection from $P^4$ to the space of convex quadrilaterals?
Specifically, I'm looking for a continuous $f:P^4\to P^4$ such that:
[convexity] ...
user44143
3
votes
1
answer
159
views
Is there a geometric interpretation of a Zariski dense surface subgroup?
Is there a geometric interpretation of a surface subgroup being Zariski dense? Or, conversely, given a $\Pi_1$ injective surface in a 3-manifold, is there a geometric or topological requirement on the ...
- 33
3
votes
1
answer
432
views
Relation between conjugacy class, quotient isomorphism class, and signature of Fuchsian groups
Let $\Gamma\le SL(2,\mathbb{Z})$ be a finite index subgroup, not necessarily "congruence".
Let $c_4,c_6$ be the number of conjugacy classes of elements of order 4 and 6 respectively, let $c_{-1}$ be ...
- 7,527
3
votes
1
answer
253
views
Constructing a homology class of degree $d(d-1)/2$ in $H_3(S^3)$
There is a nice construction of a class of degree $d^2$ in $H_3(S^3)$. Take a class $h$ of degree $d$ in $H_1(S^1)$, and then take its join with itself: $h*h$ is degree $d^2$ in $H_3(S^1*S^1)$, and $S^...
- 6,292
3
votes
1
answer
159
views
Which automorphisms on $H_{1}(M^{3})$ are induced by homotopy equivalences?
Let $M^{3}$ be a closed orientable 3-manifold, and $\phi:H_{1}(M;\mathbb{Z})\to H_{1}(M;\mathbb{Z})$ be an automorphism of abelian groups.
My question is: Is there any characterization of $\phi$ ...
- 31
3
votes
1
answer
1k
views
Orientation of a "glued"-manifold
Im wondering if there's a short way to prove that when two manifolds with diffeomorphic boundaries are glued together along the boundaries the orientations of these must be inverse to each other. That ...
- 947
3
votes
0
answers
120
views
Signature vs commensurability
If a closed oriented $4n$-dimensional manifold $M$ has an orientation-reversing homeomorphism, then the signature $\sigma(M)$ of the intersection form vanishes. More generally, $\sigma(M) = 0$ if $M$ ...
- 41
3
votes
0
answers
227
views
Classifying spaces beyond CW complexes
We know that for a reasonable topological group $G$ (say a compact Lie group) admits a classifying space for $G$-bundles within the category of countable CW complexes. That means, there is a space $BG$...
- 803
3
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0
answers
638
views
What are some of the big open problems in $4$-manifold theory?
I've recently been studying some Manifold Theory and got very interested in their topological as well as geometric properties. From my understanding of the current literature, most the big and ...
- 139
3
votes
0
answers
429
views
"Maehara-style" proof of Jordan-Schoenflies theorem?
The highest upvoted answer to this old question Nice proof of the Jordan curve theorem? is a proof by Ryuji Maehara. I personally really liked/appreciated that Maehara's proof is
A) a fairly ...
- 833
3
votes
0
answers
115
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 ...
3
votes
0
answers
258
views
Determinantal variety
It is well known in literature about the determinantal varieties, symmetric determinantal varities, skew-symmetric determinantal varieties. Is it possible to study determinantal varieties over the ...
- 31
3
votes
0
answers
195
views
Is there such an isotopy for every homology sphere?
Let $n \geq 3$, and $\Sigma^{n-1} \subset \mathbf{S}^n$ be a smoothly and properly embedded, orientable, and connected submanifold of the sphere. This divides the sphere into two open sets, $U_-$ and $...
- 5,048
3
votes
0
answers
122
views
Is there a framed nullbordism of $T^4$ with an action of $T^4$ that extends the self-action?
Under the identification of the stable homotopy groups with the (stably) framed bordism groups, it is well known that $\eta\in\pi_1\mathbb{S}$ is represented by $S^1$ with its Lie group framing. ...
- 2,052
3
votes
0
answers
130
views
Functoriality of short exact sequence of fundamental groups induced by a Seifert fibered space
Let $M$ be a Seifert fibered space over an orbifold $B$. Assume that $B$ is good and has infinite orbifold fundamental group. Then it is well known that there is a short exact sequence. $$1\to {\Bbb Z}...
- 585
3
votes
0
answers
137
views
Intersection number for 4 manifold with boundary
Let $X$ be a closed oriented smooth $4$-manifold. Suppose there is an embedding $\Sigma\to X$, it is known that the self-intersection number satisfies $[\Sigma]\cdot [\Sigma]=\pm\int_\Sigma c_1(N)$, ...
- 1,915
3
votes
0
answers
158
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What is the meaning of local inertia conjugation property?
In Hatcher, Allen; Lochak, Pierre; Schneps, Leila, On the Teichmüller tower of mapping class groups, J. Reine Angew. Math. 521, 1-24 (2000). ZBL0953.20030., we have:
Abstract. Let $\widehat{G T}^{1}$ ...
- 119
3
votes
0
answers
113
views
Extending good covers of $\partial M$ to $M$
Suppose $M$ is an $n$-dimensional manifold with boundary with a free action of a finite group $G$. Suppose one has an equivariant collar $c: \partial M \times [0,1) \rightarrow M$. An open cover is ...
- 5,849
3
votes
0
answers
164
views
Equivalent condition for compact group to act transitively
Let $ M $ be a connected manifold. Let $ \pi_1(M) $ be the fundamental group of $ M $.
Suppose there exists a compact group $ K $ that acts transitively on $ M $. Then $ \pi_1(M) $ must have a finite ...
- 4,081
3
votes
0
answers
60
views
Embedding with vanishing images of homotopy groups
Let $f$ be a locally flat embedding from $S^2 \times \mathbb R^2$ to $S^2 \times \mathbb R^2$ such that $f_*(\pi_k(S^2 \times \mathbb R^2))=0$ for any $k \ge 2$.
Can we find a domain $U$ that contains ...
- 891
3
votes
0
answers
282
views
Commutator length of the fundamental group of some grope
A popular way to describe a grope as the direct limit $L$ of a nested sequence of compact 2-dimensional polyhedra
$L_0 \to L_1 \to L_2 \to \cdots$
obtained as follows. Take $L_0$ as some $S_g$, an ...
- 2,083
3
votes
0
answers
670
views
Elementary reference for Borel-Moore/locally finite homology
There is a homology theory called "Borel-Moore" or "locally finite" homology, which can either be constructed by using locally-finite chains or by more advanced sheaf-theoretic ...
- 2,533