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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeFeb 23rd 2017
   • (edited Feb 23rd 2017)
   • PermaLink
   Author: Urs
   Format: MarkdownItexI gave _[[Jones' theorem]]_ (long requested at _[[Hochschild homology]]_) a quick statement and references. Copied this also to the entries _[[free loop space]]_, _[[cyclic loop space]]_ and _[[cyclic homology]]_ and _[[Sullivan models of free loop spaces]]_: *** Let $X$ be a [[simply connected topological space|simply connected]] [[topological space]]. The [[ordinary cohomology]] $H^\bullet$ of its free loop space is the [[Hochschild homology]] $HH_\bullet$ of its [[singular cohomology|singular chains]] $C^\bullet(X)$: $$ H^\bullet(\mathcal{L}X) \simeq HH_\bullet( C^\bullet(X) ) \,. $$ Moreover the $S^1$-equivariant cohomology of the loop space, hence the ordinary cohomology of the [[cyclic loop space]] $\mathcal{L}X/^h S^1$ is the [[cyclic homology]] $HC_\bullet$ of the singular chains: $$ H^\bullet(\mathcal{L}X/^h S^1) \simeq HC_\bullet( C^\bullet(X) ) $$ ([Loday 11](#Loday11)) If the [[coefficients]] are [[rational numbers|rational]], and $X$ is of [[finite type]] then this may be computed by the _[[Sullivan model for free loop spaces]]_, see there the section on _[Relation to Hochschild homology](Sullivan+model+of+free+loop+space#RelationToHochschildHomology)_. In the special case that the [[topological space]] $X$ carries the structure of a [[smooth manifold]], then the singular cochains on $X$ are equivalent to the [[dgc-algebra]] of [[differential forms]] (the [[de Rham algebra]]) and hence in this case the statement becomes that $$ H^\bullet(\mathcal{L}X) \simeq HH_\bullet( \Omega^\bullet(X) ) \,. $$ $$ H^\bullet(\mathcal{L}X/^h S^1) \simeq HC_\bullet( \Omega^\bullet(X) ) \,. $$ This is known as _[[Jones' theorem]]_ ([Jones 87](#Jones87)) An [[(infinity,1)-category theory|infinity-category theoretic]] proof of this fact is indicated at _[Hochschild cohomology -- Jones' theorem](Hochschild+cohomology#JonesTheorem)_.

   I gave Jones’ theorem (long requested at Hochschild homology) a quick statement and references. Copied this also to the entries free loop space, cyclic loop space and cyclic homology and Sullivan models of free loop spaces:

   ---

   Let $X$ be a simply connected topological space.

   The ordinary cohomology $H^\bullet$ of its free loop space is the Hochschild homology $HH_\bullet$ of its singular chains $C^\bullet(X)$:

   $$H^\bullet(\mathcal{L}X) \simeq HH_\bullet( C^\bullet(X) ) \,.$$

   Moreover the $S^1$-equivariant cohomology of the loop space, hence the ordinary cohomology of the cyclic loop space $\mathcal{L}X/^h S^1$ is the cyclic homology $HC_\bullet$ of the singular chains:

   $$H^\bullet(\mathcal{L}X/^h S^1) \simeq HC_\bullet( C^\bullet(X) )$$

   (Loday 11)

   If the coefficients are rational, and $X$ is of finite type then this may be computed by the Sullivan model for free loop spaces, see there the section on Relation to Hochschild homology.

   In the special case that the topological space $X$ carries the structure of a smooth manifold, then the singular cochains on $X$ are equivalent to the dgc-algebra of differential forms (the de Rham algebra) and hence in this case the statement becomes that

   $$H^\bullet(\mathcal{L}X) \simeq HH_\bullet( \Omega^\bullet(X) ) \,.$$ $$H^\bullet(\mathcal{L}X/^h S^1) \simeq HC_\bullet( \Omega^\bullet(X) ) \,.$$

   This is known as Jones’ theorem (Jones 87)

   An infinity-category theoretic proof of this fact is indicated at Hochschild cohomology – Jones’ theorem.