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

5 votes
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A coproduct of $C^\ast$-algebras

Given two locally compact spaces $X$ and $Y$ then the product $X \times Y$ is an open subset inside $\overline{X} \times \overline{Y}$, where $\overline{X}$ and $\overline{X}$ are the one point compac …
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10 votes
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A C*-algebra enjoying some different C*-norms

No that's not possible (except the trivial case). Any $*$-homomorphism between $C^*$-algebras is automatically contractive, and if it is injective then it is isometric. You can apply this to the ident …
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6 votes
Accepted

What is the Gelfand dual of an open surjection?

After more thought, I think the correct statement is the following: Theorem: Let $\pi : X \to Y$ be a continuous map between compact Hausdorff spaces. Then the following condition are equivalents: (a) …
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7 votes
1 answer
230 views

Free extension of algebra for an operad

I fix $C$ a symmetric monoidal model category (with a cofibrant unit if it helps). I'm assuming that it is closed, or at least that the tensor product commutes to colimits in each variable. If $X$ is …
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18 votes
Accepted

Non-commutative duality I: Which C*-algebras are (isomorphic to a) convolution algebra?

The main obstruction to this kind of duality is not so much that not every $C^*$-algebra is a convolution algebra (though, at least if we don't use twisted convolution algebra, there are known obstruc …
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12 votes
Accepted

Can one associate a "nice" topos to a von Neumann algebra?

(I'm going to be a bit informal to be able to go to the point relatively directly, but if you want more details on some specific aspect. I can try to add them) Toposes are closely related to topologic …
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6 votes

What does it mean for a category to admit direct integrals?

The following is an argument for showing that "having direct integral" is definitely not a property nor a "property-like-structure" of $W^*$-categegories, but a real, non-trivial additional structure. …
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2 votes

KMS-states of Bost-Connes type system

$\pi$ is an irreducible representation. So because of Schur lemma and the double commutant theorem the map $\pi:A \rightarrow B(H)$ is surjective. Now the state $\phi$ is defined as a normale state o …
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2 votes

Does every integer map generate a von Neumann algebra of type I?

I think I have an example: Precisely, I will construct an integer function $m$ such that $M$ is bounded and the algebra $\mathcal{M}$ contains a corner which is the von Neuman algebra completion of a …
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5 votes

Route to Alain Connes'work about classification of injective factors

I would strongly recommend to have a look (and to always keep available) to the books by Takesaki "The theory of Operator algebras" I,II and III You might not need to know everything that is in these …
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8 votes
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How the modular theory of von Neumann algebras, deal with generating C*-algebras?

All groups algebra are trivial examples because for them the modular time evolution is (can be chosen) trivial: the modular time evolution attached to a state is trivial if and only if the state is a …
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7 votes
1 answer
479 views

Two notions of bundle of C* algebras

One can find in the literature two notions of $C^*$-algebra over a topological space $X$. The first is as the data of an open surjection $ \pi: B \rightarrow X$ together with the structure of a $C^*$ …
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1 vote
Accepted

On the second dual of $C[0,1]$

It is easy to see that $\int \psi d\delta_t$ where $\delta_t$ is the Dirac mass at $t$ is $\psi(\{t\})$ So you are starting from a $T \in C([0,1])^{**}$ and you are attaching to it the function $t \m …
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8 votes
1 answer
175 views

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

If $O$ is a (strongly ?) self absorbing $C^*$-algebra, one has an equivalence relation on (separable) $C^*$-algebras: "being $O$-stably isomorphic" i.e. $A$ and $B$ are $O$-stably isomorphic if and on …
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4 votes
0 answers
134 views

References for a lemma about compact operators on a Hilbert module

I am looking for a reference for the following result: If $A$ and $B$ are C* algebras, $H$ is a right Hilbert $A$-modules, $\phi :A \rightarrow B$ is a morphism, and assume that there is a map $\eta …
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