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A C*-algebra is a complex Banach algebra together with an isometric antilinear involution satisfying (a b)* = b* a* and the C*-identity ‖a* a‖ = ‖a‖². Related tags: [banach-algebras], [von-neumann-algebras], [operator-algebras], [spectral-theory].

5 votes

When is a groupoid the path groupoid of a graph?

This is an answer to the question: "Given a $C^\ast$-algebra $A$ that shares some properties of (higher-rank) graph algebras (such as separability, nuclearity, UCT, K-theoretic properties), can I conc …
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2 votes

Relative K-theory and split exact sequences of C* algebras

The unitalization case $A=J^+$ is treated in Blackadar's $K$-theory for Operator Algebras. In Proposition 5.4.1 he directly shows that $$ K_0(J^+,J)\cong\ker(K_0(J^+)\to K_0({J^+}/J)). $$
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4 votes
0 answers
454 views

What is the spectrum of the commutative C*-algebra I have constructed here?

Let $B$ and $F$ be compact Hausdorff spaces. Let $E\to B$ be a fiber bundle with fibre $F$ and structure group $\mathrm{Homeo}(F)$, the group of homeomorphisms of $F$. I think this induces a fiber b …
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13 votes
1 answer
1k views

What is the commutative analogue of a C*-subalgebra?

Using the duality between locally compact Hausdorff spaces and commutative $C^*$-algebras one can write down a vocabulary list translating topological notions regarding a locally compact Hausdorff spa …
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0 votes
Accepted

Relation between the UCT and Künneth ($C^*$-algebras)

It is absolutely true that these two theorems are conceptually related. But instead of one being a consequence of the other, both rather follow from the same machinery being applied to slightly differ …
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2 votes

Gelfand duality in NCG

Concerning your last question, I would say you should view your C*-algebra itself as the (coordinate ring on the) "non-commutative topological space." The spaces you suggest are commutative. Your C*-a …
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9 votes
2 answers
2k views

What does the representation theory of the reduced C*-algebra correspond to?

Let $G$ be a locally compact group. The group C*-algebra $C^* (G)$ is designed to come with a natural bijection between its (nondegenerate) representations and the (strongly continuous, unitary) repre …
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9 votes

$C^{*}$-correspondences viewed as generalized endomorphisms

Expanding my comment as per suggestion above. All this is explained in more detail in the reference I gave though. A correspondence from $A$ to $B$ is a Hilbert $B$-module on which $A$ acts non-degen …
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1 vote
Accepted

Unitization via "End points compactification"

There is Noncommutative End Theory by Akemann and Eilers.
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6 votes
1 answer
870 views

Sources for exact triangles in triangulated categories.

The other day I came across the statement that in the triangulated category $\mathfrak{KK}$ (of C*-algebras with KK-groups as morphism sets) "there are many other sources of exact triangles besides ex …
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