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11 votes
Accepted

$*$-algebras, completions, and $K$-theory

Any infinite discrete group $\Gamma$ with Kazhdan's property (T) gives an example. Since it is not amenable, the full and reduced C*-algebras (which are both completions of the group algebra) do not ...
user131654's user avatar
9 votes
Accepted

Role of the UCT problem in classification theory for C*-algebras

Remark: The UCT-sequence is not correct as you stated it, it does not only involve the $K_0$-groups. Regarding your second quastion: I highly recommend the book "Classification of nuclear $C^*$-...
Sabrina Gemsa's user avatar
9 votes
Accepted

K-Theory of $C^{*}(X)$

The group you describe should be the infinite symmetric group $S_{\infty}$. The $K$-theory of its $C^*$-algebra has been determined by Kerov and Vershik in The K -functor (Grothendieck group) of the ...
Ulrich Pennig's user avatar
7 votes
Accepted

Is there a $ H_* H^* $-theory which is naturally a common generalization both of singular homology and de Rham (or singular) cohomology?

Yes. There is the "singular chains" functor $C_*:\mathcal{S} \to \mathcal{D}(\mathbb{Z})$, where $\mathcal{S}$ denotes your favorite category of spaces, and $\mathcal{D}(\mathbb{Z})$ is the ...
Achim Krause's user avatar
  • 9,507
6 votes
Accepted

Bass and Quillen K-theory

I read that Bass K-theory is sometimes called the non-connective K-theory Basically, Quillen $K$-theory can be viewed as a spectrum (in the sense of topology), instead of just as a space (this is an ...
Joe Berner's user avatar
6 votes
Accepted

example of a non-amenable l.c. group such that $C_r^*(G)$ satisfies the UCT

Both $C^\ast(\mathbb F_2)$ and $C^\ast_r(\mathbb F_2)$ satisfy the UCT. This is the special case of the following: $\mathbf{Theorem}$. If $G$ and $H$ are countable, discrete, amenable groups, then $C^...
Jamie Gabe's user avatar
  • 2,346
6 votes

Is there a categorical version of the splitting principle?

I don't think there can be a reasonable such splitting principle, even in the weakest sense you asked about (i.e. $K_0(\mathsf R) \to K_0(\mathsf R')$ is injective) and in the case when the ground ...
Dan Petersen's user avatar
  • 39.5k
4 votes
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Morita equivalence of the invariant uniform Roe algebra and the reduced group C*-algebra

To define the Roe algebra abstractly, we need a suitable covariant representation of the $\Gamma$-$C^\ast$-algebra $(C_0(X), \Gamma)$ on some Hilbert space $H$. In concrete situations, one usually ...
Rudolf Zeidler's user avatar
3 votes

Is there a $ H_* H^* $-theory which is naturally a common generalization both of singular homology and de Rham (or singular) cohomology?

Let me give some references for bivariant "de Rham theory" for locally convex and $C^*$-algebras. We know that, roughly speaking, Hochschild homology (equipped with an $S^1$-action) is a &...
Z. M's user avatar
  • 2,446
3 votes

KK-theoretical proof of Atiyah-Singer index theorem

I find the proof in the recent paper of Kasparov G. Kasparov. Elliptic and transversally elliptic index theory from the viewpoint of KK-theory. J. Noncommut. Geom., 10(4):1303–1378, 2016 ...
Maxim Braverman's user avatar
3 votes
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reference for KK theory

If you want to learn more about KK-theory there is a book by Kjeld Knudsen Jensen and Klaus Thomsen with the title "Elements of KK-theory". You can have a look there. I would also recommend those ...
far's user avatar
  • 154
2 votes
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description of a map in KK-theory

I don't think that there is anything special about $\mathcal O_\infty$ being used here. One observation that might help is that the map $KK(A, \mathcal O_\infty)\to KK(\mathbb C, \mathcal O_\infty)$ ...
user85913's user avatar
  • 830
2 votes

How to define an equivariant Kasparov's KK-theory map?

Isn't this treated in Claude Schochet's 1992 paper "On Equivariant Kasparov Theory and Spanier-Whitehead Duality"? Also, if you want more references, I'd recommend using Google Scholar to ...
David White - gone from MO's user avatar
1 vote

Producing $K$-homology cycles from $KK$-cycles

Here are just some trivial observations that came to mind after thinking about this a little longer: You are essentially asking for a canonical class in the $K$-homology group $K^0(B) = KK(B,\mathbb{C}...
Ulrich Pennig's user avatar
1 vote

Différences between KKO and KKR in Kasparov theory

I think the difference is because one has real Clifford algebras $Cl_{p,q}(\mathbb{R})$ (indexed by two variables $p,q$), but only complex Clifford algebras $Cl_n(\mathbb{C})$. My main concern is ...
hänsel's user avatar
  • 675
1 vote

Self adjoint operators in Kasparov-Modules

What is meant is that $T$ and $(T+T^*)/2$ differ by a compact operator. More precisely: $$\pi(a) (T - (T+T^*)/2)= \pi(a) (T/2 - T^*/2) \equiv \pi(a) (T/2-T/2)=0$$ for all $a \in A$ modulo $K(E)$, ...
hänsel's user avatar
  • 675
1 vote

Homotopy equivalence of Kasparov's $KK$-Theory

It is really the same thing as for ordinary homotopy. Mainly a concatenation. I will write for a space $X$, $XB$ the algebra of continous functions from $X$ to $B$. All the other notations follow ...
InfiniteLooper's user avatar
1 vote

The Green-Julg Theorem

For $G$ a finite group, this is part 3 of Theorem 1.22 in the preprint A stable ∞-category for equivariant KK-theory by Ulrich Bunke, Alexander Engel and Markus Land. More precisely, they prove an ...
Bastiaan Cnossen's user avatar

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