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- Discussion Type
- discussion topicorbifold
- Category Latest Changes
- Started by Urs
- Comments 30
- Last comment by Urs
- Last Active May 29th 2019

I am moving the following old query box exchange from orbifold to here.

old query box discussion:

I am confused by this page. It starts out by boldly declaring that “An orbifold is a differentiable stack which may be presented by a proper étale Lie groupoid” but then it goes on to talk about the “traditional” definition. The traditional definition definitely

**does not**view orbifolds as stacks. Neither does Moerdijk’s paper referenced below — there orbifolds form a 1-category.Personally I am not completely convinced that orbifolds are differentiable stacks. Would it not be better to start out by saying that there is no consensus on what orbifolds “really are” and lay out three points of view: traditional, Moerdijk’s “orbifolds as groupoids” (called “modern” by Adem and Ruan in their book) and orbifolds as stacks?

Urs Schreiber: please, go ahead. It would be appreciated.

end of old query box discussion

- Discussion Type
- discussion topicAlbert Einstein
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 29th 2019

added this pointer:

Peter Coles,

*Einstein, Eddington, and the 1919 Eclipse*(arxIv:astro-ph/0102462)(on the experimental confirmation of general relativity)

- Discussion Type
- discussion topicAlexey Petrov
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 28th 2019

brief

`category:people`

-entry for hyperlinking references at*effective field theory*

- Discussion Type
- discussion topiceffective quantum field theory
- Category Latest Changes
- Started by Urs
- Comments 11
- Last comment by Urs
- Last Active May 28th 2019

at effective quantum field theory I have started writing an Idea-section and added more reference

- Discussion Type
- discussion topicsuperselection theory
- Category Latest Changes
- Started by Tim_van_Beek
- Comments 39
- Last comment by Urs
- Last Active May 28th 2019

I tried to explain what a superselection sector is which is less easy than one would think…of course what I would really like to do is to explain some DHR-superselection theory and there one can of course cite the mathematical definition without any further explanation of the origins :-)

- Discussion Type
- discussion topicPure subobject
- Category Latest Changes
- Started by Zhen Lin
- Comments 14
- Last comment by nLab edit announcer
- Last Active May 28th 2019

Started pure subobject. I wish someone would tell me the intuitive reason for their importance though!

- Discussion Type
- discussion topiccategory theory
- Category Latest Changes
- Started by Eric
- Comments 68
- Last comment by Thomas Holder
- Last Active May 27th 2019

I removed some spam on category theory.

- Discussion Type
- discussion topicpartial recursive function
- Category Latest Changes
- Started by Sam Staton
- Comments 6
- Last comment by Sam Staton
- Last Active May 27th 2019

- Discussion Type
- discussion topicintersecting D-brane model
- Category Latest Changes
- Started by Urs
- Comments 6
- Last comment by Urs
- Last Active May 27th 2019

**Edit to**: intersecting D-brane model by Urs Schreiber at 2018-04-01 00:55:01 UTC.**Author comments**:hyperlinked pointer to textbook by Ibanez-Uranga

- Discussion Type
- discussion topicchaos
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 27th 2019

a stub, for the moment just so as to give a home to

- William Lawvere,
*Functional Remarks on the General Concept of Chaos*, IMA reprint 87, 1984 (pdf)

- William Lawvere,

- Discussion Type
- discussion topicdiscrete and codiscrete topology
- Category Latest Changes
- Started by Urs
- Comments 10
- Last comment by Urs
- Last Active May 27th 2019

created discrete and codiscrete topology

- Discussion Type
- discussion topicknot complement
- Category Latest Changes
- Started by Urs
- Comments 3
- Last comment by Richard Williamson
- Last Active May 27th 2019

- Discussion Type
- discussion topictranscendental syntax
- Category Latest Changes
- Started by nLab edit announcer
- Comments 1
- Last comment by nLab edit announcer
- Last Active May 26th 2019

- Discussion Type
- discussion topicVitalik Buterin
- Category Latest Changes
- Started by zskoda
- Comments 1
- Last comment by zskoda
- Last Active May 26th 2019

- Discussion Type
- discussion topiccartesian monoidal category
- Category Latest Changes
- Started by David_Corfield
- Comments 2
- Last comment by nLab edit announcer
- Last Active May 26th 2019

Added a link to Todd’s nice page on free cartesian category.

- Discussion Type
- discussion topicweak bialgebra
- Category Latest Changes
- Started by zskoda
- Comments 2
- Last comment by zskoda
- Last Active May 24th 2019

To support mentioning weak wreath product in a parallel discussion with Urs, I created a stub for weak bialgebra with redirect weak Hopf algebra.

- Discussion Type
- discussion topicR-parity
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 23rd 2019

some minimum, in order to give a home to today’s

- Dong-Yang Wang, Ya-Dong Yang, Xing-Bo Yuan,
*$b \to c \tau \bar \nu$ decays in supersymmetry with R-parity violation*(arXiv:1905.08784)

- Dong-Yang Wang, Ya-Dong Yang, Xing-Bo Yuan,

- Discussion Type
- discussion topicRR-field tadpole cancellation
- Category Latest Changes
- Started by Urs
- Comments 16
- Last comment by Urs
- Last Active May 23rd 2019

started some bare minimum omn RR-field tadpole cancellation. Currently I am using this just to complement discussion at

*intersecting D-brane models*

- Discussion Type
- discussion topicKO-theory
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 23rd 2019

added pointer to today’s

- Daniel Grady, Hisham Sati,
*Twisted differential KO-theory*(arXiv:1905.09085)

- Daniel Grady, Hisham Sati,

- Discussion Type
- discussion topicHandbook of Homotopy Theory
- Category Latest Changes
- Started by Urs
- Comments 6
- Last comment by DavidRoberts
- Last Active May 23rd 2019

- Discussion Type
- discussion topich-principle
- Category Latest Changes
- Started by David_Corfield
- Comments 4
- Last comment by Tim_Porter
- Last Active May 22nd 2019

- Discussion Type
- discussion topicfractional M2-brane
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019

bare minimum, just for completeness, to go with

*3d-3d correspondence*

- Discussion Type
- discussion topicduality in string theory -- contents
- Category Latest Changes
- Started by Urs
- Comments 6
- Last comment by Urs
- Last Active May 22nd 2019

- Discussion Type
- discussion topic3d-3d correspondence
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019

- Discussion Type
- discussion topicvolume conjecture
- Category Latest Changes
- Started by Urs
- Comments 5
- Last comment by Urs
- Last Active May 22nd 2019

added rough statement of the general volume conjecture (here), just so that I could point to

- Qingtao Chen, Tian Yang,
*A volume conjecture for a family of Turaev-Viro type invariants of 3-manifolds with boundary*(arXiv:1503.02547)

which seems to be regarded as a landmark result.

- Qingtao Chen, Tian Yang,

- Discussion Type
- discussion topicconformally flat manifold
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019

- Discussion Type
- discussion topichyperbolic manifold
- Category Latest Changes
- Started by Urs
- Comments 3
- Last comment by Urs
- Last Active May 22nd 2019

created

*hyperbolic manifold*in order to record a reference on the relation between volumes of hyperbolic 3-folds and their Chern-Simons/Dijkgraaf-Witten invariants by Zickert.

- Discussion Type
- discussion topicS-brane
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019

- Discussion Type
- discussion topicKK-compactifications of M-theory -- table
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019

- Discussion Type
- discussion topicM-theory on hyperbolic manifolds
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 22nd 2019