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2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry bundle bundles calculus categories category category-theory chern-weil-theory cohesion cohesive-homotopy-type-theory cohomology colimits combinatorics complex complex-geometry computable-mathematics computer-science constructive cosmology deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry digraphs duality elliptic-cohomology enriched fibration finite foundations functional-analysis functor galois-theory gauge-theory gebra geometric-quantization geometry graph graphs gravity group group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory homological homological-algebra homology homotopy homotopy-theory homotopy-type-theory index-theory infinity integration integration-theory itex k-theory lie-theory limits linear linear-algebra locale localization logic mathematics measure measure-theory modal modal-logic model model-category-theory monads monoidal monoidal-category-theory morphism motives motivic-cohomology nlab noncommutative noncommutative-geometry number-theory of operads operator operator-algebra order-theory pages pasting philosophy physics planar pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory string string-theory superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topology topos topos-theory tqft type type-theory universal variational-calculus

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- Discussion Type
- discussion topicholographic light front QCD
- Category Latest Changes
- Started by Urs
- Comments 4
- Last comment by Urs
- Last Active May 12th 2020

am splitting this off from

*holographic QCD*, since the latter is getting too crowded. Prompted by today’s- Mohammad Ahmady,
*Holographic light-front QCD in B meson phenomenology*(arXiv:2001.00266)

- Mohammad Ahmady,

- Discussion Type
- discussion topicmassive Yang-Mills theory
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active May 11th 2020

- Discussion Type
- discussion topicexotic brane
- Category Latest Changes
- Started by Luigi
- Comments 4
- Last comment by Luigi
- Last Active May 11th 2020

- Discussion Type
- discussion topicKan complex
- Category Latest Changes
- Started by Urs
- Comments 15
- Last comment by Tim_Porter
- Last Active May 11th 2020

added a sentence to the Idea-section at Kan complex

- Discussion Type
- discussion topicKan fibration
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Tim_Porter
- Last Active May 11th 2020

added the pointers to the combinatorial proofs of the fiberwise detection of acyclicity of Kan fibrations, currently discussed on the AlgTop list, to the nLab here.

- Discussion Type
- discussion topicpromonoidal category
- Category Latest Changes
- Started by Mike Shulman
- Comments 15
- Last comment by Théo de Oliveira S.
- Last Active May 10th 2020

I moved the definition of promonoidal categories from Day convolution to promonoidal category, and expanded on it a bit.

- Discussion Type
- discussion topicweak model category
- Category Latest Changes
- Started by Dmitri Pavlov
- Comments 16
- Last comment by Hurkyl
- Last Active May 9th 2020

- Discussion Type
- discussion topicpremodel category
- Category Latest Changes
- Started by Dmitri Pavlov
- Comments 6
- Last comment by Hurkyl
- Last Active May 9th 2020

- Discussion Type
- discussion topicHomePage
- Category Latest Changes
- Started by Urs
- Comments 60
- Last comment by nLab edit announcer
- Last Active May 9th 2020

I have added at

*HomePage*in the section*Discussion*a new sentence with a new link:If you do contribute to the nLab, you are strongly encouraged to similarly drop a short note there about what you have done – or maybe just about what you plan to do or even what you would like others to do. See Welcome to the nForum (nlabmeta) for more information.

I had completly forgotton about that page

*Welcome to the nForum (nlabmeta)*. I re-doscivered it only after my recent related comment here.

- Discussion Type
- discussion topiclist of journals publishing category theory - mucked up
- Category Latest Changes
- Started by Tim_Porter
- Comments 1
- Last comment by Tim_Porter
- Last Active May 9th 2020

This page has been ‘mucked up’. The table has been destroyed giving just a block of text. I could roll back but thought it better for people to see the mess!

- Discussion Type
- discussion topicBarr's theorem
- Category Latest Changes
- Started by Urs
- Comments 3
- Last comment by Thomas Holder
- Last Active May 9th 2020

created stub for Barr’s theorem (If a statement in geometric logic is deducible from a geometric theory using classical logic and the axiom of choice, then it is also deducible from it in constructive mathematics.)

- Discussion Type
- discussion topicKripke's schema
- Category Latest Changes
- Started by nLab edit announcer
- Comments 2
- Last comment by Urs
- Last Active May 9th 2020

- Discussion Type
- discussion topicpushout-product axiom
- Category Latest Changes
- Started by Hurkyl
- Comments 1
- Last comment by Hurkyl
- Last Active May 9th 2020

- Discussion Type
- discussion topicflat space holography
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

- Discussion Type
- discussion topiclax functor
- Category Latest Changes
- Started by varkor
- Comments 1
- Last comment by varkor
- Last Active May 8th 2020

- Discussion Type
- discussion topicwalking structure
- Category Latest Changes
- Started by Mike Shulman
- Comments 5
- Last comment by varkor
- Last Active May 8th 2020

I added to walking structure a 2-categorical theorem that implies that usually “the underlying X of the walking X is the initial X”. This fact seems like it should be well-known, but I don’t offhand know a reference for it, can anyone give a pointer?

- Discussion Type
- discussion topicbaryon number
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

a stub, for the moment just to ungray a link at

*exotic meson*

- Discussion Type
- discussion topicexotic meson
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

starting some minimum, to go with

*XYZ meson*and*tetraquark*

- Discussion Type
- discussion topich1-meson
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

- Discussion Type
- discussion topicb1-meson
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

- Discussion Type
- discussion topicbivector
- Category Latest Changes
- Started by zskoda
- Comments 3
- Last comment by Urs
- Last Active May 8th 2020

I made some changes to bivector. While the idea section is correct (and should be strictly adhered to!) but the previous definition is wrong in general! The previous definition is consistent and used in wikipedia but it misses both the direct relation of bivectors, trivectors and general polyvectors to determinants as well as the standard nontrivial usage of bivectors in analytic geometry wher bivectors define equivalence classes of parallelograms and in particular with a point in space given define an affine plane. If we adhere to wikipedia and not to standard treatments in geometry (e.g. M M Postnikov, Analytic geometry) then we miss the nontriviality of the notion of bivector and its meaning which is more precise than that of a general element in the second exterior power.

Bivector in a vector space $V$ is not any element in the second exterior power, but a DECOMPOSABLE vector in the second tensor power – in general dimension just such elements in $\Lambda^2 V$ have the intended geometric meaning and define vector 2-subspaces and of course affine 2-subspaces if a point in the 2-subspace is given. It is true that every bivector in 2-d or in 3-d space is decomposable, but in dimension 4 this is already not true. Thus the bivectors form a vector space just in the dimensions up to $3$. Similarly, trivectors form a vector space just in the dimensions up to $4$. In the context of differential graded algebras, polyvector fields are usually taken as arbitrary elements in the exterior powers of vector fields.

- Discussion Type
- discussion topichadron Kaluza-Klein theory
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active May 8th 2020

I am giving this its own entry, to go alongside

*hadron supersymmetry*, but right now it contains mustly just the commented references from*hadrons as KK-modes of 5d Yang-Mills theory – references*

- Discussion Type
- discussion topichadrons as KK-modes of 5d Yang-Mills theory -- references
- Category Latest Changes
- Started by Urs
- Comments 2
- Last comment by Urs
- Last Active May 8th 2020

- Discussion Type
- discussion topicMichael Atiyah
- Category Latest Changes
- Started by Urs
- Comments 7
- Last comment by Urs
- Last Active May 8th 2020

- Discussion Type
- discussion topicPaul Fendley
- Category Latest Changes
- Started by Tim_Porter
- Comments 1
- Last comment by Tim_Porter
- Last Active May 8th 2020

- Discussion Type
- discussion topicAlexander Popov
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

brief

`category:people`

-entry for hyperlinking references at*Skyrmion*and*D=5 Yang-Mills theory*

- Discussion Type
- discussion topicTatiana Ivanova
- Category Latest Changes
- Started by Urs
- Comments 1
- Last comment by Urs
- Last Active May 8th 2020

brief

`category:people`

-entry for hyperlinking references at*Skyrmion*and*D=5 Yang-Mills theory*

- Discussion Type
- discussion topicAdS-QCD correspondence
- Category Latest Changes
- Started by Urs
- Comments 51
- Last comment by David_Corfield
- Last Active May 8th 2020

- Discussion Type
- discussion topicWilliam Dwyer
- Category Latest Changes
- Started by Dmitri Pavlov
- Comments 3
- Last comment by Dmitri Pavlov
- Last Active May 8th 2020

- Discussion Type
- discussion topicinhomogeneous cosmology
- Category Latest Changes
- Started by Urs
- Comments 26
- Last comment by Urs
- Last Active May 8th 2020

started something. For the moment really just a glorified pointer to Buchert et al. 15 and putting Scharf 13 into perspective