Homotopy theory is an important sub-field of algebraic topology. It is mainly concerned with the properties and structures of spaces which are invariant under homotopy. Chief among these are the homotopy groups of spaces, specifically those of spheres. Homotopy theory includes a broad set of ideas ...
0
votes
0answers
100 views
On Gromov's Theorem on Symplectic Homotopy
I want to understand the proof of the following theorem due to Gromov which I'll state in the context of Euclidean spaces. While I tried to read the proof from Macduff-Salamon, it turned out that my ...
3
votes
0answers
80 views
When does a map in the stable homotopy group gets killed when smashed with cone of itself?
Consider an element $e \in \pi_n^s(S^0)$, in the stable homotopy groups of sphere. Let $C$ denote the spectrum which is cone of $e$, i.e. $C$ fits in the cofiber sequence
$$ S^n \to S^0 \to C.$$
...
14
votes
1answer
379 views
Free Loop-Space Recognition Principle
It is well-known that one can detect based loopspaces using the machinery of operads. Namely, given a group-like space $X$ with an action of $\mathbb{E}_n$-operad, then it is homotopy equivalent as an ...
4
votes
1answer
133 views
fibrant generation of $sSet_{Quillen}$?
I wonder if someone has proved that $sSet_{Quillen}$ is not a fibrantly generated model structure ? Do we know something about the possible fibrant generation of $sSet_{Quillen}$ ?
Thanks
1
vote
1answer
53 views
Cartesian products between cofibrant simplicial presheaves
Let $Psh(\mathcal{C})$ be the category of simplicial presheaves equipped with the projective model structure. The cartesian product between two representables presheaves is clearly again representable ...
2
votes
0answers
112 views
A Cartesian model structure (and straightening for) on $n$-trivial simplicial sets
A pair $(X,tX)$, with $X$ a simplicial set and $tX$ a collection of simplices of $X$, is said to be stratified if no $0$-simplex is in $X$ and all degenerate simplices of $X$ are in $tX$. Recall a ...
17
votes
1answer
388 views
Super-cobordisms
One can construct the $d$-dimensional bordism category by declaring the objects to be the $(d-1)$-dimensional compact manifolds without boundary and the morphisms the $d$-dimensional bordisms between ...
5
votes
1answer
134 views
homotopy tensor product of functors and bar construction
I'm trying to take familiarity with homotopy theory and I have the following questions. Let $\mathcal{C}$ be a small category, and let $F\: : \:\mathcal{C}\to \mathcal{M}$ that take values in a ...
0
votes
0answers
73 views
homotopy end/coend [on hold]
I would like to compute the homotopy end/coend of a bifunctor $S\: : \: \mathcal{C}\times \mathcal{C}^{op}\to \mathcal{E}$ where $\mathcal{C}$ is a small category and $\mathcal{E}$ is a model ...
-3
votes
0answers
90 views
cohomology of permutation group of order power of $2$
Let $S_k$ be symmetric group of order $k$. What is
$$
H^*(BS_{2^k};\mathbb{Z}_2)?
$$
$$
H^*(BS_{2^k};\mathbb{Z})?
$$
I only know the case $k=1$.
3
votes
0answers
173 views
What are iterated cobar constructions?
In Beck's paper "On H-spaces and Infinite Loop Spaces", he states that every algebra over the monad $\Omega^k$$\Sigma^k$ is a $k$-fold loop space. He proves the trivial case k = 0 when this is the ...
2
votes
1answer
125 views
Fibration $p : \tilde Y \to Y$ with discrete fiber induces bijection $p_*:[X, \tilde Y]_* \to [X, Y]_*$
If $X$ is simply connected, locally path connected space and $p : \tilde Y \to Y$ is a covering map then it is easy to show that it induces bijection $p_*:[X, \tilde Y]_* \to [X, Y]_*$. Let's weak ...
4
votes
3answers
284 views
Need examples of homotopy orbit and fixed points
I am no expert in equivariant homotopy theory. Let's say, I am planing to give a talk on homotopy fixed points and orbits. My audience will be graduate students who are doing algebraic topology or ...
9
votes
3answers
254 views
Maps with Hopf invariant zero are suspensions
Let $h:\pi_{2n-1}(S^n) \rightarrow \mathbb{Z}$ be the Hopf invariant. I believe that in the same paper that proves his suspension theorem, Freudenthal proved that if $x \in \pi_{2n-1}(S^n)$ satisfies ...
4
votes
1answer
231 views
Descent properties of spaces
I am trying to make sense of what is written in Rezk's draft http://www.math.uiuc.edu/~rezk/i-hate-the-pi-star-kan-condition.pdf
In particular, I am referring to Proposition 2.3, which is there stated ...
1
vote
1answer
61 views
homotopic maps of locally finite spaces
It is well known that if $X,Y$ are $T_0$ Alexandrov spaces then they are just posets. With every such spaces we can associate an abstract simplicial complex $K(X)$ where the simplices are nonempty ...
11
votes
1answer
227 views
What is obstructing two stably-isomorphic vector bundles from being isomorphic?
The specific situation is the following:
Let $n>0$ be a natural number, let $X$ be a finite CW complex of dimension $n$, and let $\xi_0,\xi_1$ be oriented real vector bundles of rank $n$ over $X$ ...
5
votes
0answers
114 views
Actions of cofibrations and induced maps of cofibres
Working in some nice category of based topological spaces (compactly generated with CW homotopy type, say) suppose we have a homotopy commutative diagram
$$
\begin{array}{ccccc}
& & j & ...
2
votes
0answers
62 views
Equivariant model structure on $G-\mathrm{Gpd}$
Let's denote $G\text{-}\mathrm{Gpd}$ the presheaf category $[\mathbf{B}G, \mathrm{Gpd}]$. Now assume that $\mathrm{Gpd}$ is endowed with its natural model structure where weak equivalences are ...
2
votes
1answer
136 views
Lorentzian metrics on the torus up to continuos deformations
Any two Riemannian metrics can easily be deformed into each other, only obtaining positive definite metrics in between.
However, for metrics of other signatures this might not be possible.
Which ...
6
votes
1answer
435 views
Homologically distinct infinite loop structures on a space
Let $X$ be a connected pointed topological space equipped with two different actions of $E_\infty$-operad. Each action provides a collection of deloopings $X_i$, where $X_0 = X$ and $\Omega X_i$ is ...
2
votes
0answers
97 views
Is the Thom diagonal co-$E_\infty$?
Given a map of spaces $f:X\to BGL_1(R)$ for $R$ an $E_\infty$-ring spectrum (of course this can be done more generally) one can produce a Thom spectrum $Mf$ by a number of methods. Let's denote such a ...
5
votes
2answers
152 views
For a quasicategory $C$, why is $\mathrm{Fun}(\Lambda^2_0,C) \to \mathrm{Fun}(\Delta^{\{2\}},C) \cong C$ a cocartesian fibration?
More generally, I expect that the following is true:
Let $D$ be a diagram quasicategory, let $d \in D$ be a vertex, and use this to define $D' = D \amalg_{\Delta^{\{0\}}} \Delta^1$. Then ...
2
votes
1answer
131 views
A Dold-Thom style construction of a cohomology class from a sphere bundle
Re-reading my comment to the question Pontryagin class of quaternionic line bundle I suddenly realized that I do not understand something crucial about it. For the purposes of that crucial thing let ...
6
votes
1answer
186 views
Is there an analog of compactified moduli spaces(/stacks) for smooth manifolds?
This question has been inspired by an answer to the question Reference request: Topology on the space of smooth compact submanifolds; I've asked it in a comment to that answer but then decided to make ...
2
votes
1answer
129 views
Two-bridge knots and CW-complex
The fundamental group of any two-bridge knot K in $\mathbb{S}^3$ has a presentation with two generators and one relation.
On the other hand, it's possible to provide a CW-complex with only one 0-cell ...
26
votes
2answers
812 views
Maps which induce the same homomorphism on homotopy and homology groups are homotopic
I am interested in the following question. Are maps which induce the same homomorphism on homotopy and homology groups homotopic? I am sure the answer is no, however I cannot imagine how to construct ...
2
votes
1answer
191 views
When are homotopy categories of model categories closed modules over the homotopy category of $(\infty, 1)$-categories?
Let $\mathrm{Quillen}$ be the model category of simplicial sets with the Quillen model structure, and $\mathrm{Joyal}$ the model category of simplicial sets with the Joyal model structure.
As is ...
-2
votes
0answers
205 views
Constructing model category from given category [migrated]
Given a model category $\mathcal{M}$, Goerss and Hopkins constructed a subcategory (see Structured Ring Spectra, p. 160) $\mathbf{E}$ of $\mathcal{M}$ such that:
If $X\in\mathbf{E}$ and $Y$ is ...
3
votes
1answer
132 views
homology of configuration spaces of non-compact manifolds
Let $M$ be a manifold.
Let $F(M,n)$ be the configuration space of $n$-tuples on $M$.
Let $B(M,n)=F(M,n)/S_n$, where $S_n$ is the symmetric group of order $n$, be the corresponding unordered ...
1
vote
0answers
152 views
Under which conditions the inclusion of a sub-simplicial set of the nerve of a category is a Joyal equivalence?
Let $i: X \to \mathrm{N}\mathcal C$ be a monomorphism in the category of simplicial sets, with $\mathcal C$ a category and $\mathrm{N}\mathcal C$ its nerve. I am looking for sufficient conditions (and ...
2
votes
1answer
121 views
recognising weak equivalences of simplicial sets
$\require{AMScd}$ I am interested in detecting using a lifting property when a map $f:X\to Y$ in $sSet$ (with the standard Kan model structure) is a weak equivalence. In the paper Weak Equivalences ...
1
vote
0answers
100 views
Properties of “incomplete finite simplicial complexes”
Definition: We say that $K'$ is an incomplete finite simplicial complex if there exists a finite simplicial complex $K$ such that $|K'|=|K|\backslash Y$ where $Y$ is a union of some open faces of K.
...
6
votes
0answers
134 views
Connection between quasifibrations and homotopy cartesian squares
Let me first fix the definitions.
A map $p\colon E\rightarrow B$ is called a quasi-fibration, iff the canonical inclusion $p^{-1}(b)\rightarrow hofib_b(p)$ is a weak equivalence for all for all $b\in ...
8
votes
0answers
251 views
Homological algebra is linearized homotopical algebra?
I have stumbled across statements like
Homological algebra is linearized homotopical algebra.
Chain complexes are linearizations of simplicial complexes.
The Dold-Kan correspondence was ...
5
votes
0answers
140 views
G-spaces and SG-module spectra
This question is related to the one here, but has a slightly different angle.
Let $G$ be a topological group and let $X$ be a $G$-space. Taking the suspension spectrum $\Sigma^{\infty}_+ X$ (in my ...
0
votes
0answers
61 views
cohomology of labelled configuration space & relation with braid space
Let $M$ be a manifold and $(X,*)$ be a pointed topological space. ( If we want, we can let $M=S^2,S^1\times \mathbb{R},etc.$)
Let $F(M,k)$ be the ordered configuration space of $k$-tuples on $M$.
...
7
votes
3answers
350 views
Mathematical value of constructing sphere eversions
I am extremely impressed by the work that has been done constructing sphere eversions, and other similar explicit geometrical proofs. In particular, surely nobody can fail to be impressed by the ...
3
votes
2answers
216 views
cohomology algebra of braid spaces, configuration spaces
In Homology of $C_{n+1}$-spaces, $n\geq 0$, F.R. Cohen, Lecture Notes in Mathematics, Vol. 533, Chapter 5, 6, 7, 8, 9, 10, 11, the cohomology algebra $H^*(B(\mathbb{R}^{n+1},p),\mathbb{Z}_p)$, for ...
13
votes
1answer
211 views
Embedding of two-dimensional CW complexes which induces a zero homomorphism on second homotopy groups
I am interested in the following question which I asked at MSE and did not get any clues. How to find three two-dimensional CW complexes $K_1, K_2, K_3$ with non-trivial $\pi_2$ and injective ...
1
vote
1answer
137 views
fiber sequence of principal bundles
Let $G$ be a group, either a Lie group or a discrete group. Let a principal $G$-bundle
$$
G\to E\to B,$$
then $B=E/G$, the orbit space under action of $G$.
Let $BG$ be the classifying space of $G$.
...
6
votes
1answer
341 views
Generalized Thom spectra
I am currently trying to wrap my head around all kinds of different definitions of the notion of (generalized) Thom spectrum. My setup is as follows: Suppose I have a commutative (symmetric) ring ...
1
vote
2answers
99 views
Reference for the proof of a neighbourhood characterisation of cofibrations
I am interested in a reference for the proof of the following
theorem for $A,X$ being CGWH topological spaces.
Let $A\subset X$ be a closed subspace,
such that there exists a continuous $\phi : ...
4
votes
1answer
214 views
Relation between cohomology of ordered and unordered configuration spaces
Let $M$ be a manifold. Then $F(M,k)/\Sigma_k$, the unordered configuration space of $k$ points, is obtained as a quotient of $F(M,k)$, the ordered configuration space of $k$ points, by the group ...
0
votes
0answers
118 views
Quillen adjunction betwen simplicial presheaves and cochain complexes
Let $sPsh(\mathcal{C})$ the category of simplicial presheaves over a small category $\mathcal{C}$. Let $Ch^{*}_{\geq 0}$ be the category of positively graded cochain complexes of modules over a field ...
-1
votes
1answer
83 views
cohomology algebra of unordered configuration space on Euclidean space
In Homology of $C_{n+1}$-spaces, $n\geq 0$, F.R. Cohen, Lecture Notes in Mathematics, Vol. 533, page 210 (the preface part before contents):
Line 2: ... is used to compute the precise algebra ...
4
votes
0answers
124 views
cohomology algebra of unordered configuration space with coefficients the finite fields
in the paper The cohomology algebra of unordered configuration spaces (Y. Félix, D. Tanré, J. London Math. Soc., 2005), Theorem 4:
Let $M$ be an odd-dimensional, compact, closed, oriented manifold. ...
1
vote
1answer
105 views
Does the nerve functor preserve fibrations?
As asked in the title but more specifically: does the nerve functor from Cat to sSet map a fibration between groupoids to a Kan fibration ?
By fibration of groupoids I mean a fibration for the ...
27
votes
2answers
949 views
Is there a “simplification” functor in algebraic topology?
Recall that a space (=CW complex) is called simple if it is connected, the fundamental group is abelian, and the fundamental group acts trivially on all higher homotopy groups. Call Simp(X) a ...
2
votes
2answers
239 views
Can homotopy pullbacks of spaces be checked on fibers?
As should be clear, I would like to know if it is true that a given commmutative square of spaces (i.e. simplicial sets) is a homotopy pullback iff the induced map on each homotopy fiber is a weak ...
