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Homotopy theory, homological algebra, algebraic treatments of manifolds.

8 votes

Does there exist a GRR-like generalization of the AS Index Theorem?

I'm sorry for the self-citation. But your question is largely answered in the monograph Coherent Sheaves, Superconnections, and Riemann-Roch-Grothendieck, or the arxiv version, joint work of Jean-Mich …
Zhaoting Wei's user avatar
  • 9,019
5 votes
0 answers
121 views

How to see $\delta_2(\hat{\chi}(V))=\chi(V)$ in differential cohomology?

I'm reading the paper "Differential Characters and Geometric Invariants" by Cheeger and Simons. In Page 62 the authors defined the differential Euler character $\hat{\chi}(V)\in \hat{H}^{2n-1}(M, \mat …
Zhaoting Wei's user avatar
  • 9,019
5 votes
2 answers
574 views

Can we define fundamental groups functorially for non-pointed path connected topological spa...

Let $\text{ppTop}$ denote the category of pointed and path connected topological spaces with morphisms base-preserve continuous maps. The fundamental group gives a functor $FG: \text{ppTop}\to \text{G …
Zhaoting Wei's user avatar
  • 9,019
3 votes
1 answer
458 views

Why do we need cofiltered condition on the index category in the definition of pro-categories?

Let $\mathcal{C}$ be a category. The pro-category pro-$\mathcal{C}$ is defined as (see this nLab page) follows: its objects are diagrams $F: D\to \mathcal{C}$ where $D$ is a small cofiltered category. …
Zhaoting Wei's user avatar
  • 9,019
6 votes
2 answers
329 views

Where to find the proof that these two version of simplicial homotopy are equivalent?

Let $f,g: X_{\bullet}\to Y_{\bullet}$ be two simplicial maps between simplicial sets. We say $f$ and $g$ are (strictly) simplicial homotopic if there exists a simplicial map $H: X_{\bullet}\times I_{ …
Zhaoting Wei's user avatar
  • 9,019
1 vote
1 answer
245 views

Does a topological hypercover always have free degeneracies?

This question arises when I am reading Dugger and Isaksen's "Hypercovers in topology". According to Definition 4.1 in that paper, A hypercover of a space $X$ is an augmented simplicial space $U_*\to X …
Zhaoting Wei's user avatar
  • 9,019
3 votes

Closure relations between Bruhat cells on the flag variety

For a first introduction you can read Michel Brion's "http://arxiv.org/pdf/math/0410240v1.pdf". He gives a nice introduction (for G=GL(n)) in Section 1. I'm not sure whether your curve method works b …
Zhaoting Wei's user avatar
  • 9,019
7 votes
1 answer
418 views

How does the kernel of the map $\Omega^{\bullet}(X)\rightarrow \Omega^{\bullet}(G\times X)$ ...

This question may be trivial for experts. Consider a (compact, connected) smooth manifold $X$ and a (compact connected) Lie group $G$ act on $X$. Then we have the action map $$ \mu: G\times X\rightarr …
Zhaoting Wei's user avatar
  • 9,019
3 votes
1 answer
567 views

What is the "higher version" of chain homotopy in singular homology?

In basic algebraic topology, we know the following well-known chain homotopy theorem: Let $X$ be a topological space and $I=[0,1]$ be the unit interval. Let $S_*(X)$ and $S_*(X\times I)$ be the sing …
Zhaoting Wei's user avatar
  • 9,019
7 votes
3 answers
1k views

Is there a "by hand" proof on the symmetry of the Atiyah class of $TX$?

Let X be a complex manifold and $TX$ its tangent bundle. The Atiyah class $\alpha(E)\in \text{Ext}^1(E\otimes TX, E)$ for a vector bundle $E$ is defined to be the obstruction of the global existence o …
Zhaoting Wei's user avatar
  • 9,019
8 votes
1 answer
369 views

Do we have a "topological assembly map" in the Baum-Connes conjecture?

In the equivariant Atiyah-Singer index theorem, when $G$ is a compact group acting on a manifold $M$ and $R(G)$ is the representation ring of $G$. We have the analytic index $$ \text{a-ind}: K^*_G(TM) …
Zhaoting Wei's user avatar
  • 9,019
2 votes
Accepted

Definition of the homological Chern character

I like this question! I think this problem (the Chern character of K-homology) has been studied and solved by Alain Connes in his paper "Noncommutative differential geometry" in 1985. He indeed used c …
Zhaoting Wei's user avatar
  • 9,019
10 votes
0 answers
737 views

What is Quillen's contribution to index theorem?

In the book "Heat Kernels and Dirac Operators" by Berline, Getzler and Vergne it is said that "Our book is based on a simple principle, which we learned from D. Quillen: Dirac operators are a quantiza …
Zhaoting Wei's user avatar
  • 9,019
4 votes
2 answers
514 views

Equivariant K-theory of $S^1$-action on $S^2$

Is there any references for the structure of the equivariant K-theory $K_{S^1}(S^2)$ where the action of $S^1$ on $S^2$ is defined to be rotation about the $z$-axis? What is the ring structore of $K_{ …
Zhaoting Wei's user avatar
  • 9,019
20 votes
2 answers
3k views

Is there any "deep" relation between the localization theorem of equivariant cohomology and ...

First let's consider equivariant cohomology: if a compact Lie group $G$ acts on a compact manifold $M$. We have the equivariant cohomology $ H_G(M)$ defined as the cohomology of the cochain complex $( …
Zhaoting Wei's user avatar
  • 9,019

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