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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeOct 29th 2009
   • (edited Oct 29th 2009)
   • PermaLink
   Author: Urs
   Format: Markdowncreated [[spectral triple]], but so far a bit bizarre: I give an unorthodox category-theoretic VAGUE definition, which I have reason to think is the _right_ one and then I record an unusual reference on vonNeumann spectral triple (just because at MO somebody <a href="http://mathoverflow.net/questions/3150/non-commutative-geometry-from-von-neumann-algebras">asked</a> for this and I don't like to dig out a link just to throw it away after one reference use like a paper napkin )

   created spectral triple, but so far a bit bizarre:

   I give an unorthodox category-theoretic VAGUE definition, which I have reason to think is the right one

   and then I record an unusual reference on vonNeumann spectral triple (just because at MO somebody asked for this and I don't like to dig out a link just to throw it away after one reference use like a paper napkin )

2. • CommentRowNumber2.
   • CommentAuthorzskoda
   • CommentTimeOct 30th 2009
   • PermaLink
   Author: zskoda
   Format: TextBut von Neumann algebras are a special case of C-star algebras (usually not interesting for the same purposes to which C-star algebras are).

   But von Neumann algebras are a special case of C-star algebras (usually not interesting for the same purposes to which C-star algebras are).
3. • CommentRowNumber3.
   • CommentAuthorUrs
   • CommentTimeOct 30th 2009
   • PermaLink
   Author: Urs
   Format: MarkdownI have to admit I haven't actually looked at that article on "vonNeumann spectra triples". But I guess some aspect of the definition must differ, otherwise the author wouldn't have called it that way.

   I have to admit I haven't actually looked at that article on "vonNeumann spectra triples". But I guess some aspect of the definition must differ, otherwise the author wouldn't have called it that way.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeNov 23rd 2010
   • (edited Nov 23rd 2010)
   • PermaLink
   Author: Urs
   Format: MarkdownItexadded references on point particle limits of 2d CFTs to spectral triples, and also some other links

   added references on point particle limits of 2d CFTs to spectral triples, and also some other links

5. • CommentRowNumber5.
   • CommentAuthorUrs
   • CommentTimeNov 23rd 2010
   • PermaLink
   Author: Urs
   Format: MarkdownItexmore references (now also the standard ones! :-)

   more references (now also the standard ones! :-)

6. • CommentRowNumber6.
   • CommentAuthorDavid_Corfield
   • CommentTimeNov 23rd 2010
   • PermaLink
   Author: David_Corfield
   Format: MarkdownItexIf >A spectral triple is algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and generalizes it to noncommutative geometry. Is it possible to have algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and string structure (and then fivebrane structure) and generalizes it to noncommutative geometry?

   If

   A spectral triple is algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and generalizes it to noncommutative geometry.

   Is it possible to have algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and string structure (and then fivebrane structure) and generalizes it to noncommutative geometry?

7. • CommentRowNumber7.
   • CommentAuthorzskoda
   • CommentTimeNov 23rd 2010
   • (edited Nov 23rd 2010)
   • PermaLink
   Author: zskoda
   Format: MarkdownItexIt is a $Spin^{\mathbb{C}}$ structure not usual $Spin$ structure if this makes a difference.

   It is a $Spin^{\mathbb{C}}$ structure not usual $Spin$ structure if this makes a difference.

8. • CommentRowNumber8.
   • CommentAuthorUrs
   • CommentTimeNov 23rd 2010
   • (edited Nov 23rd 2010)
   • PermaLink
   Author: Urs
   Format: MarkdownItex> Is it possible to have algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and string structure That's supposed to be what a 2-spectral triple is, which is supposed to be the data given by a 2d superconformal QFT that behaves as if it is the worldvolume theory of the heterotic/type II superstring. Pretty close to fully formalizing this is the work surveyed at [[(2,1)-dimensional Euclidean field theories and tmf]]. (The String structure condition that you are looking for appears right at the beginning in this entry.) But there are many other known approaches that must be effectively encodings of the same kind of data, such as certain vertex operator algebras, speicifcally certain chiral de Rham complexes. Also Costello has more on this in terms of his factorization algebras. Hopefully eventually somebody writes it all out nicely. But the general upshot is: yes, the algebraic data we are talking about it is that encoding the worldvolume theory of the fundamental super $p$-brane propagating on the corresponding type of geoemtry. There ought to be also a 6-spectral triple that corresponds to geometries with Fivebrane structures, yes, but I am not aware of much concrete progress in getting that. > It is a $Spin^{\mathbb{C}}$ structure not usual $Spin$ structure if this makes a difference. I think these variants all corespond to slight variants in the axioms of the spectral triple and can all be accounted for. For instance see the sentence right beneath theorem 1.2 <a href="http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2088v1.pdf#page=3">here</a> which says that the "reality condition" on the spectral triple makes it pick Spin-geometry among $Spin^{c}$-geometries.

   Is it possible to have algebraic data that mimics the geometric data provided by a smooth Riemannian manifold with spin structure and string structure

   That’s supposed to be what a 2-spectral triple is, which is supposed to be the data given by a 2d superconformal QFT that behaves as if it is the worldvolume theory of the heterotic/type II superstring.

   Pretty close to fully formalizing this is the work surveyed at (2,1)-dimensional Euclidean field theories and tmf. (The String structure condition that you are looking for appears right at the beginning in this entry.)

   But there are many other known approaches that must be effectively encodings of the same kind of data, such as certain vertex operator algebras, speicifcally certain chiral de Rham complexes. Also Costello has more on this in terms of his factorization algebras. Hopefully eventually somebody writes it all out nicely.

   But the general upshot is: yes, the algebraic data we are talking about it is that encoding the worldvolume theory of the fundamental super $p$-brane propagating on the corresponding type of geoemtry. There ought to be also a 6-spectral triple that corresponds to geometries with Fivebrane structures, yes, but I am not aware of much concrete progress in getting that.

   It is a $Spin^{\mathbb{C}}$ structure not usual $Spin$ structure if this makes a difference.

   I think these variants all corespond to slight variants in the axioms of the spectral triple and can all be accounted for. For instance see the sentence right beneath theorem 1.2 here which says that the “reality condition” on the spectral triple makes it pick Spin-geometry among $Spin^{c}$-geometries.

9. • CommentRowNumber9.
   • CommentAuthorUrs
   • CommentTimeNov 23rd 2010
   • PermaLink
   Author: Urs
   Format: MarkdownItexI have slightly expanded [[2-spectral triple]] in reply to David's question.

   I have slightly expanded 2-spectral triple in reply to David’s question.

10. • CommentRowNumber10.
    • CommentAuthorDavid_Corfield
    • CommentTimeNov 24th 2010
    • PermaLink
    Author: David_Corfield
    Format: MarkdownItexThanks. What about the "...and generalizes it to noncommutative geometry" part? Does that make any sense in the 2-spectral situation?

    Thanks. What about the “…and generalizes it to noncommutative geometry” part? Does that make any sense in the 2-spectral situation?

11. • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeNov 24th 2010
    • (edited Nov 24th 2010)
    • PermaLink
    Author: Urs
    Format: MarkdownItex> What about the "...and generalizes it to noncommutative geometry" part? Does that make any sense in the 2-spectral situation? Yes, it makes sense. You need to find the characterization of the algebraic properties of those 2d SCFTs that come from your desired target space (Riemannian with string structure, say). Then you just declare that _every_ SCFT with these abstract properties defines a "noncommutative string Riemannian manifold", even if its space of states is not that of a string on a Riemannnian manifold. A simple example of the general kind of approach here is spelled out in some detail in the article by Roggenkamp and Wendland that is cited in the entry. They show that the family of 2d CFTs that go by the name "minimal models" are "noncommutative 2-geometry" deformations of the standard interval $[0,1]$ equipped with a dilaton field. Whatever that means, think of it as analogous geometric data as saying "Riemannian manifold with string structure". So generally you can look at an abstract 2d (S)CFT $Z$ and ask what type of genuine $\sigma$-model SCFT it behaves like. Then you can say that $Z$ is a "noncommutative" generalization of such a type of geometry. This is a standard and basic way to go about things in string theory, but there it is not usually formalized or thought of in quite the way we are after here. But for instance one of the early major results in string theory was the _flop transition_ which is related to this phenomenon: what is called the _flop transition_ is a continuous path in the space of 2-spectral triples=2d SCFTs which goes through points that are genuine geometries at the beginning and the end, but passes in between through a point which is not an ordinary geometry (the "Gepner model"). So it connects two types of ordinary ("commutative") geometries that are not connected in the space of ordinary geometries. In fact they have different topology (that's what the word "flop" alludes to).

    What about the “…and generalizes it to noncommutative geometry” part? Does that make any sense in the 2-spectral situation?

    Yes, it makes sense. You need to find the characterization of the algebraic properties of those 2d SCFTs that come from your desired target space (Riemannian with string structure, say). Then you just declare that every SCFT with these abstract properties defines a “noncommutative string Riemannian manifold”, even if its space of states is not that of a string on a Riemannnian manifold.

    A simple example of the general kind of approach here is spelled out in some detail in the article by Roggenkamp and Wendland that is cited in the entry. They show that the family of 2d CFTs that go by the name “minimal models” are “noncommutative 2-geometry” deformations of the standard interval $[0,1]$ equipped with a dilaton field. Whatever that means, think of it as analogous geometric data as saying “Riemannian manifold with string structure”.

    So generally you can look at an abstract 2d (S)CFT $Z$ and ask what type of genuine $\sigma$-model SCFT it behaves like. Then you can say that $Z$ is a “noncommutative” generalization of such a type of geometry.

    This is a standard and basic way to go about things in string theory, but there it is not usually formalized or thought of in quite the way we are after here. But for instance one of the early major results in string theory was the flop transition which is related to this phenomenon: what is called the flop transition is a continuous path in the space of 2-spectral triples=2d SCFTs which goes through points that are genuine geometries at the beginning and the end, but passes in between through a point which is not an ordinary geometry (the “Gepner model”). So it connects two types of ordinary (“commutative”) geometries that are not connected in the space of ordinary geometries. In fact they have different topology (that’s what the word “flop” alludes to).

12. • CommentRowNumber12.
    • CommentAuthorUrs
    • CommentTimeNov 24th 2010
    • PermaLink
    Author: Urs
    Format: MarkdownItexat [[flop transition]] there is now a tiny little bit of literature on what I just mentioned

    at flop transition there is now a tiny little bit of literature on what I just mentioned

13. • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeApr 8th 2014
    • PermaLink
    Author: Urs
    Format: MarkdownItexSombody emailed me asking for and suggesting more accurate historical references at _[[spectral triple]]_ and more emphasis on the essentially equivalent and older concept of unbounded Fredholm modules. I have added those references, added the relevant cross-pointers, and highlighted the relation to Fredholm modules more. Of course the entry still does not contain actual precise content. Maybe somebody with energy and time comes along and feels like adding something.

    Sombody emailed me asking for and suggesting more accurate historical references at spectral triple and more emphasis on the essentially equivalent and older concept of unbounded Fredholm modules.

    I have added those references, added the relevant cross-pointers, and highlighted the relation to Fredholm modules more.

    Of course the entry still does not contain actual precise content. Maybe somebody with energy and time comes along and feels like adding something.

14. • CommentRowNumber14.
    • CommentAuthorTim_Porter
    • CommentTimeApr 8th 2014
    • (edited Apr 8th 2014)
    • PermaLink
    Author: Tim_Porter
    Format: MarkdownItexThe webpage link at [[Henri Moscovici]] was dead. I changed it. Please check it is the one needed as it does not seem to lead anywhere!

    The webpage link at Henri Moscovici was dead. I changed it. Please check it is the one needed as it does not seem to lead anywhere!

15. • CommentRowNumber15.
    • CommentAuthorUrs
    • CommentTimeOct 29th 2019
    • PermaLink
    Author: Urs
    Format: MarkdownItexadded pointer to today's * Latham Boyle, Shane Farnsworth, _The standard model, the Pati-Salam model, and "Jordan geometry"_ ([arxiv:1910.11888](https://arxiv.org/abs/1910.11888)) <a href="https://ncatlab.org/nlab/revision/diff/spectral+triple/28">diff</a>, <a href="https://ncatlab.org/nlab/revision/spectral+triple/28">v28</a>, <a href="https://ncatlab.org/nlab/show/spectral+triple">current</a>

    added pointer to today’s

    • Latham Boyle, Shane Farnsworth, The standard model, the Pati-Salam model, and “Jordan geometry” (arxiv:1910.11888)

    diff, v28, current

16. • CommentRowNumber16.
    • CommentAuthorUrs
    • CommentTimeDec 2nd 2019
    • PermaLink
    Author: Urs
    Format: MarkdownItexadded pointer to today's * Ludwik Dabrowski, Andrzej Sitarz, _Multiwisted real spectral triples_ ([arXiv:1911.12873](https://arxiv.org/abs/1911.12873)) <a href="https://ncatlab.org/nlab/revision/diff/spectral+triple/29">diff</a>, <a href="https://ncatlab.org/nlab/revision/spectral+triple/29">v29</a>, <a href="https://ncatlab.org/nlab/show/spectral+triple">current</a>

    added pointer to today’s

    • Ludwik Dabrowski, Andrzej Sitarz, Multiwisted real spectral triples (arXiv:1911.12873)

    diff, v29, current

17. • CommentRowNumber17.
    • CommentAuthorUrs
    • CommentTimeMar 10th 2020
    • PermaLink
    Author: Urs
    Format: MarkdownItexadded pointer to today's * R. da Rocha, A. A. Tomaz, _Hearing the shape of inequivalent spin structures and exotic Dirac operators_ ([arXiv:2003.03619](https://arxiv.org/abs/2003.03619)) <a href="https://ncatlab.org/nlab/revision/diff/spectral+triple/31">diff</a>, <a href="https://ncatlab.org/nlab/revision/spectral+triple/31">v31</a>, <a href="https://ncatlab.org/nlab/show/spectral+triple">current</a>

    added pointer to today’s

    • R. da Rocha, A. A. Tomaz, Hearing the shape of inequivalent spin structures and exotic Dirac operators (arXiv:2003.03619)

    diff, v31, current

18. • CommentRowNumber18.
    • CommentAuthorUrs
    • CommentTimeJun 15th 2022
    • PermaLink
    Author: Urs
    Format: MarkdownItexadded ([here](https://ncatlab.org/nlab/show/spectral+triple#OverJordanAlgebras)) pointer to today's * Fabien Besnard, Shane Farnsworth, *Particle models from special Jordan backgrounds and spectral triples* $[$[arXiv:2206.07039](https://arxiv.org/abs/2206.07039)$]$ <a href="https://ncatlab.org/nlab/revision/diff/spectral+triple/33">diff</a>, <a href="https://ncatlab.org/nlab/revision/spectral+triple/33">v33</a>, <a href="https://ncatlab.org/nlab/show/spectral+triple">current</a>

    added (here) pointer to today’s

    • Fabien Besnard, Shane Farnsworth, Particle models from special Jordan backgrounds and spectral triples $[$arXiv:2206.07039$]$

    diff, v33, current