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1. • CommentRowNumber1.
   • CommentAuthorJames Francese
   • CommentTimeJul 16th 2018
   • (edited Jul 16th 2018)
   • PermaLink
   Author: James Francese
   Format: MarkdownItexI am a newcomer to non-commutative geometry and really enjoying the literature. I have read several of the classic papers, assisted by the excellent lecture notes *Homological Methods in Non-commutative Geometry* by Kaledin. I have also read the papers by Reyes, Heunen, and van den Berg on the obstructions to extending the Zariski site to $\mathsf{Ring}$ in various ways. Now I see on the nLab page for [[noncommutative algebraic geometry]] there is the added statement: >This is the reason why non-commutative algebraic geometry is phrased in other terms, mostly in terms of monoidal categories “of (quasicoherent) abelian sheaves” (“2-rings”). Are there a few names people can drop for me, or even specific papers, which are most significant for following up on this hint? Before coming across this page I worked out some things for sheaf theory on bicategories (e.g. of noncommutative algebras), but feel I must be on well-trodden ground.

   I am a newcomer to non-commutative geometry and really enjoying the literature. I have read several of the classic papers, assisted by the excellent lecture notes Homological Methods in Non-commutative Geometry by Kaledin. I have also read the papers by Reyes, Heunen, and van den Berg on the obstructions to extending the Zariski site to $\mathsf{Ring}$ in various ways. Now I see on the nLab page for noncommutative algebraic geometry there is the added statement:

   This is the reason why non-commutative algebraic geometry is phrased in other terms, mostly in terms of monoidal categories “of (quasicoherent) abelian sheaves” (“2-rings”).

   Are there a few names people can drop for me, or even specific papers, which are most significant for following up on this hint? Before coming across this page I worked out some things for sheaf theory on bicategories (e.g. of noncommutative algebras), but feel I must be on well-trodden ground.

2. • CommentRowNumber2.
   • CommentAuthorUrs
   • CommentTimeJul 16th 2018
   • (edited Jul 16th 2018)
   • PermaLink
   Author: Urs
   Format: MarkdownItexThis passage means to be pointing to _[[2-algebraic geometry]]_ (pointer added now). But I am unsure how non-commutative such 2-algebraic geometry really is. I think the royal road to non-commutative geometry via higher categories is the result by Schwede-Shipley ([here](https://ncatlab.org/nlab/show/stable+(infinity%2C1)-category#AsCategoriesOfModules)) that stable $\infty$-categories that have a small set of generators are equivalently the categories of modules over $A_\infty$-ring(oid)s, hence of "quasicoherent sheaves over 'spaces' including but being more general than affine non-commutative spaces". I think this provides also the transparent picture behind Kontsevich-style NCG, where non-commutative spaces are modeled as formal duals of $A_\infty$-categories: These $A_\infty$-categories in turn are but models for stable $\infty$-categories as in Schwede-Shipley's theorem.

   This passage means to be pointing to 2-algebraic geometry (pointer added now).

   But I am unsure how non-commutative such 2-algebraic geometry really is.

   I think the royal road to non-commutative geometry via higher categories is the result by Schwede-Shipley (here) that stable $\infty$-categories that have a small set of generators are equivalently the categories of modules over $A_\infty$-ring(oid)s, hence of “quasicoherent sheaves over ’spaces’ including but being more general than affine non-commutative spaces”.

   I think this provides also the transparent picture behind Kontsevich-style NCG, where non-commutative spaces are modeled as formal duals of $A_\infty$-categories: These $A_\infty$-categories in turn are but models for stable $\infty$-categories as in Schwede-Shipley’s theorem.

3. • CommentRowNumber3.
   • CommentAuthorJames Francese
   • CommentTimeJul 16th 2018
   • (edited Jul 16th 2018)
   • PermaLink
   Author: James Francese
   Format: MarkdownItexThank you Urs, I appreciate the link. Actually, I find my thinking is getting split between Connes and Kontsevich for NCG, since I am essentially tackling problems in non-commutative analysis, but in the style of Kashiwara, Sato, etc. for algebraic analysis. In particular, I am developing a theory of sheaf cohomology in Clifford analysis which will support a kind of Riemann-Hilbert correspondence (absence of holomorphy nowithstanding). So my goal is to build a de Rham functor for certain (higher) categories of non-commutative algebras. Since Clifford algebras form a 2-cat, this is why I was drawn to sheaves on bicategories; in fact [your Cafe post](https://golem.ph.utexas.edu/category/2007/10/categorified_clifford_algebra.html) on categorified Clifford algebras and Shulman/Baez's [later commentary](https://golem.ph.utexas.edu/category/2007/10/higher_clifford_algebras.html) really encouraged me to think along these lines. The split in my thinking happens because while Clifford algebras form a von Neumann algebra (essential ingredient of spectral triples), it is not clear what geometric object should be associated with it, as a spin manifold is in the classical case; on the other hand, differential envelopes of Clifford algebras are nice to work with and one can define a Grothendieck topology on the category of such superalgebras. But again, it is not clear where the underlying geometry should come from! So that's one thing I'm struggling with...in a Clifford-analytic R-H correspondence, what should play the role of variety/manifold? It seems like that Shwede-Shipley paper is working a full level of abstraction above what I'm saying: given a dg algebra $A$, the derived category $\mathcal{D}(A)$ of (left) dg $A$-modules is a triangulated category with a homotopy theory, although I am not sure it will always be stable in their sense. Of course I mean this only in a positive light, this seems like a powerful paper.

   Thank you Urs, I appreciate the link. Actually, I find my thinking is getting split between Connes and Kontsevich for NCG, since I am essentially tackling problems in non-commutative analysis, but in the style of Kashiwara, Sato, etc. for algebraic analysis. In particular, I am developing a theory of sheaf cohomology in Clifford analysis which will support a kind of Riemann-Hilbert correspondence (absence of holomorphy nowithstanding). So my goal is to build a de Rham functor for certain (higher) categories of non-commutative algebras. Since Clifford algebras form a 2-cat, this is why I was drawn to sheaves on bicategories; in fact your Cafe post on categorified Clifford algebras and Shulman/Baez’s later commentary really encouraged me to think along these lines.

   The split in my thinking happens because while Clifford algebras form a von Neumann algebra (essential ingredient of spectral triples), it is not clear what geometric object should be associated with it, as a spin manifold is in the classical case; on the other hand, differential envelopes of Clifford algebras are nice to work with and one can define a Grothendieck topology on the category of such superalgebras. But again, it is not clear where the underlying geometry should come from! So that’s one thing I’m struggling with…in a Clifford-analytic R-H correspondence, what should play the role of variety/manifold?

   It seems like that Shwede-Shipley paper is working a full level of abstraction above what I’m saying: given a dg algebra $A$, the derived category $\mathcal{D}(A)$ of (left) dg $A$-modules is a triangulated category with a homotopy theory, although I am not sure it will always be stable in their sense. Of course I mean this only in a positive light, this seems like a powerful paper.