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Subtag of the [oa.operator-algebras] tag for questions about von Neumann algebras, that is, weak operator topology closed, unital, *-subalgebras of bounded operators on a Hilbert space.

1 vote
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Definition of Radon measure on Takesaki's first volume

Making no claims of originality, one possible proof can be obtained by combining Example 4.60, Lemma 5.11, and Lemma 3.14 in arXiv:2005.05284. This shows that for any Radon measure its algebra of equi …
Dmitri Pavlov's user avatar
2 votes
Accepted

Continuous surjection between spectra of commutative von Neumann algebras

Is it true that π maps clopen sets into clopen sets? This is true if and only if the inclusion $V_1→V_2$ is a morphism of von Neumann algebras, i.e., its image is closed in the ultraweak topology. S …
Dmitri Pavlov's user avatar
2 votes

Hochschild/cyclic homology of von Neumann algebras: useless?

I am surprised that nobody mentioned the book by Sinclair and Smith “Hochschild Cohomology of von Neumann algebras” so far. If I remember it correctly, they claim that nobody knows whether there is a …
LSpice's user avatar
  • 12.9k
13 votes
Accepted

Making sense of "every non-commutative algebra has its own internal time evolution (aka a on...

Given any von Neumann algebra $M$, we can define its noncommutative $\def\L{{\cal L}} \L^p$-spaces $\L^p(M)$ for any $\def\C{{\bf C}} p∈\C$ such that $\Re p≥0$. Here I use the notation $\L^p:={\rm L}^ …
Dmitri Pavlov's user avatar
7 votes

Quick derivation of classical probability theory from von Neumann algebraic framework

I am not sure how far you want to go, but some basics are explained in this answer: Is there an introduction to probability theory from a structuralist/categorical perspective? In particular, you have …
Dmitri Pavlov's user avatar
23 votes
Accepted

Is the opposite category of commutative von Neumann algebras a topos?

The opposite category of commutative von Neumann algebras is not a topos because categorical products with a fixed object do not always preserve small colimits. See Theorem 6.4 in Andre Kornell's Quan …
Dmitri Pavlov's user avatar
2 votes

Reference for "the algebra of multiplication by all measurable bounded functions acts in Hil...

One possible interpretation of Connes's statement is that up to an isomorphism, there is a unique faithful indecomposable representation of any commutative von Neumann algebra on a Hilbert space. Inde …
Dmitri Pavlov's user avatar
37 votes
5 answers
4k views

Reference for the Gelfand duality theorem for commutative von Neumann algebras

The Gelfand duality theorem for commutative von Neumann algebras states that the following three categories are equivalent: (1) The opposite category of the category of commutative von Neumann algebra …
6 votes
Accepted

Reference for the Gelfand duality theorem for commutative von Neumann algebras

As shown in the paper Gelfand-type duality for commutative von Neumann algebras, the following categories are equivalent. The category CSLEMS of compact strictly localizable enhanced measurable spac …
Dmitri Pavlov's user avatar
5 votes
1 answer
333 views

One-parameter semigroups of bimodules

Suppose M is a von Neumann algebra. Consider a monoidal category of bimodules over M. Here a bimodule is a Hilbert space with two normal representations of M. The monoidal structure is given by Connes …
4 votes
Accepted

On existence of certain operators in von Neumann algebra

This is false. Consider, for example, the case of M being the von Neumann algebra of bounded complex-valued functions on an infinite countable set I. It acts on the Hilbert space of square-summable fu …
Dmitri Pavlov's user avatar
2 votes

Regarding Haagerup $L^{P}$ spaces

How the norm on L^{P} space related to weight φ? The L^p-spaces and their norms are independent of the choice of the weight φ. See, for instance, the exposition by Yamagami in “Algebraic Aspects …
Dmitri Pavlov's user avatar
4 votes

Why are ultraweak *-homomorphisms the `right' morphisms for von Neumann algebras (and say, n...

A von Neumann algebra is a $C^*$-algebra $A$ that admits a predual, i.e., a Banach space $A_*$ such that there is an isomorphism $A\to(A_*)^*$. A morphism of von Neumann algebras is a morphism of $C^ …
LSpice's user avatar
  • 12.9k
6 votes
Accepted

A non-commutative Radon-Nikodym derivative.

Such t_0 is unique if its support is at most p, where p is the support of ϕ. Note that we can replace t_0 by pt_0p and the support of pt_0p is at most p. Without this additional condition t_0 is high …
Todd Trimble's user avatar
  • 53.3k
3 votes
Accepted

$e\precsim f$ and $1-e\precsim 1-f$ imply $e\sim f$?

No. Take e=0 and 0 < f < 1 such that both f and 1−f are infinite, with (1−f)~1. Then e≾f because 0≾f for any projection f. Also 1−e≾1−f because 1≾1−f, which holds by definition of f.
Dmitri Pavlov's user avatar

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