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Algebras of operators on Hilbert space, $C^*-$algebras, von Neumann algebras, non-commutative geometry

5 votes

$\mathcal{O}_{\infty}$ and $\mathcal{Z}$ stable isomorphism as equivalence

Maybe the following can count if you are willing to restrict to separable, simple, stable, nuclear $C^*$-algebras $A$ and $B$. Then the Kirchberg-Phillips Classification Theorem says that $A\otimes\ma …
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4 votes

Representation of $*$-automorphism on finite dimensional matrix algebras

As an alternative to Robin Chapman's solution, I would like to state Exercise 7.8 from Rørdam's, Larsen's and Laustsen's "Introduction to the K-theory of C*-algebras": For every unital AF-algebra …
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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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8 votes
1 answer
1k views

Why is it called *spectral* triple?

I know the definition a spectral triple and that it is some kind of non-commutative generalisation of (the ring of functions on) a compact spin manifold. But, why is it called spectral triple?
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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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10 votes

Topological K-theory for commutative C*-algebras

Any pair of abelian groups arises, up to isomorphism, as the $K$-theory groups of a commutative $C^*$-algebra. If the groups were countable, the $C^*$-algebra can be chosen to be separable. This foll …
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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

Is the square diagram of index and exponential maps in $K$-theory of $C^*$-algebras anti-com...

This is true. It follows essentially from the naturality of the boundary map with respect to morphisms of extensions. We need to show that the composition of the two boundary maps $$ K_*(A_{00})\to K_ …
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