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Hochschild/Cyclic Homologycyclic homology of von Neumann Algebrasalgebras: Uselessuseless?

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Dave Penneys
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Is there a $II_1$-factor with nontrivial Hochschild or cyclic homology/Cyclic Homology of von Neumann Algebras: Useless?

The cyclic category makes an appearance in the studyHochschild homology gives invariants of planar algebras (see arXiv:0912.1320unital). In particular $k$-algebras for $k$ a unital, every planarcommutative ring. If we let our algebra is$A$ be the group ring $k[G]$ for $G$ a finite group, we get group homology. There are plenty of other connections to homological algebra. If we use cyclic module in two wayshomology, there are connections to geometry and topology involving the Chern character. To motivate some work on planar structure for infinite index subfactors

Von Neumann algebras are complex algebras, so we can take their Hochschild and cyclic homologies. When I want to know if there is a $II_1$have asked experts in the fields of von Neumann algebras and non-factor with nontrivialcommutative geometry about what you get, I usually hear some approximation of the following: "There's also analysis in von Neumann algebras, so I wouldn't expect an algebraic invariant like Hochschild or cyclic homology to tell you anything useful."

Although this answer makes some sense, I understand thatfind it very displeasing and cryptic. Why shouldn't it tell you something? Is there are other types of homology theories thatsome way to make more sense for"it doesn't tell you anything" quantitative? Is there an example of a von Neumann algebras, but the algebraic theory is the onealgebra with nontrivial Hochschild or cyclic homology (different from that surfaces in my work.of the complex numbers)?

NOTEEDIT: After reading the responses so far, I have edited this postshould specify that I really want to make itknow if there is a focused question$II_1$-factor with a specific goal, and it no longer resembles the original postnontrivial Hochschild or cyclic (co)homology.

Is there a $II_1$-factor with nontrivial Hochschild or cyclic homology?

The cyclic category makes an appearance in the study of planar algebras (see arXiv:0912.1320). In particular, every planar algebra is a cyclic module in two ways. To motivate some work on planar structure for infinite index subfactors, I want to know if there is a $II_1$-factor with nontrivial Hochschild or cyclic homology.

I understand that there are other types of homology theories that make more sense for von Neumann algebras, but the algebraic theory is the one that surfaces in my work.

NOTE: I have edited this post to make it a focused question with a specific goal, and it no longer resembles the original post.

Hochschild/Cyclic Homology of von Neumann Algebras: Useless?

Hochschild homology gives invariants of (unital) $k$-algebras for $k$ a unital, commutative ring. If we let our algebra $A$ be the group ring $k[G]$ for $G$ a finite group, we get group homology. There are plenty of other connections to homological algebra. If we use cyclic homology, there are connections to geometry and topology involving the Chern character.

Von Neumann algebras are complex algebras, so we can take their Hochschild and cyclic homologies. When I have asked experts in the fields of von Neumann algebras and non-commutative geometry about what you get, I usually hear some approximation of the following: "There's also analysis in von Neumann algebras, so I wouldn't expect an algebraic invariant like Hochschild or cyclic homology to tell you anything useful."

Although this answer makes some sense, I find it very displeasing and cryptic. Why shouldn't it tell you something? Is there some way to make "it doesn't tell you anything" quantitative? Is there an example of a von Neumann algebra with nontrivial Hochschild or cyclic homology (different from that of the complex numbers)?

EDIT: After reading the responses so far, I should specify that I really want to know if there is a $II_1$-factor with nontrivial Hochschild or cyclic (co)homology.

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Dave Penneys
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Is there a $II_1$-factor with nontrivial Hochschild/Cyclic Homology of von Neumann Algebras: Useless or cyclic homology?

Hochschild homology gives invariantsThe cyclic category makes an appearance in the study of planar algebras (unitalsee arXiv:0912.1320) $k$-algebras for $k$ a unital, commutative ring. If we let our algebra $A$ be the group ring $k[G]$ for $G$ a finite groupIn particular, we get group homology. There are plenty of other connections to homologicalevery planar algebra. If we use cyclic homology, there are connections to geometry and topology involving the Chern character.

Von Neumann algebras are complex algebras, so we can take their Hochschild and is a cyclic homologies. When I have asked expertsmodule in the fields of von Neumann algebras and non-commutative geometry about what you get, I usually heartwo ways. To motivate some approximation of the following: "There's also analysis in von Neumann algebraswork on planar structure for infinite index subfactors, so I wouldn't expect an algebraic invariant likewant to know if there is a $II_1$-factor with nontrivial Hochschild or cyclic homology to tell you anything useful."

Although this answer makes some sense, I find it very displeasing and cryptic. Why shouldn't it tell you something? Is there some way to make "it doesn't tell you anything" quantitative? Isunderstand that there an exampleare other types of a von Neumann algebra with nontrivial Hochschild or cyclic homology (different fromtheories that ofmake more sense for von Neumann algebras, but the complex numbers)?algebraic theory is the one that surfaces in my work.

EDITNOTE: After reading the responses so far, I should specify that I really wanthave edited this post to know if there ismake it a $II_1$-factorfocused question with nontrivial Hochschild or cyclic (co)homologya specific goal, and it no longer resembles the original post.

Hochschild/Cyclic Homology of von Neumann Algebras: Useless?

Hochschild homology gives invariants of (unital) $k$-algebras for $k$ a unital, commutative ring. If we let our algebra $A$ be the group ring $k[G]$ for $G$ a finite group, we get group homology. There are plenty of other connections to homological algebra. If we use cyclic homology, there are connections to geometry and topology involving the Chern character.

Von Neumann algebras are complex algebras, so we can take their Hochschild and cyclic homologies. When I have asked experts in the fields of von Neumann algebras and non-commutative geometry about what you get, I usually hear some approximation of the following: "There's also analysis in von Neumann algebras, so I wouldn't expect an algebraic invariant like Hochschild or cyclic homology to tell you anything useful."

Although this answer makes some sense, I find it very displeasing and cryptic. Why shouldn't it tell you something? Is there some way to make "it doesn't tell you anything" quantitative? Is there an example of a von Neumann algebra with nontrivial Hochschild or cyclic homology (different from that of the complex numbers)?

EDIT: After reading the responses so far, I should specify that I really want to know if there is a $II_1$-factor with nontrivial Hochschild or cyclic (co)homology.

Is there a $II_1$-factor with nontrivial Hochschild or cyclic homology?

The cyclic category makes an appearance in the study of planar algebras (see arXiv:0912.1320). In particular, every planar algebra is a cyclic module in two ways. To motivate some work on planar structure for infinite index subfactors, I want to know if there is a $II_1$-factor with nontrivial Hochschild or cyclic homology.

I understand that there are other types of homology theories that make more sense for von Neumann algebras, but the algebraic theory is the one that surfaces in my work.

NOTE: I have edited this post to make it a focused question with a specific goal, and it no longer resembles the original post.

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