Recall from the discussion there that a string structure on manifold with spin structure is a lift of the classifying map of the tangent bundle associated to a Spin group-principal bundle through the next step in the Whitehead tower of , called – the delooping of the String group:
The names “Spin” and “String” both derive from the role these structures play in quantum field theory: a spin structure is required on for it to serve as a target space for spinning particles (superparticles), while a string structure is required for it to serves as a target for “spinning strings” – superstrings – (see heterotic string theory for more). Topologists just say (said) for and for , respectively.
It was Hisham Sati who first realized that a lift of the tangent bundle to this highly connected structure group is related to serving as a target for “spinning 5-branes” – super-5-branes – in what is called dual heterotic string theory. Following the history of the term String group he gave the topological group the name Fivebrane group: .
Accordingly, a Fivebrane structure(n) on a manifold with string structure is a lift of to
The obstruction class to this lift is a fractional multiply of the second Pontrjagin class. Namely the generator of is ,
The term “Fivebrane” apparently quickly caught on in the mathematical community, for instance in (DouglasHenriquesHill).
Since gauge theory is not just about principal bundles, but about principal bundles with connection, what matters in physics is not just the topological Spin-, String- and Fivebrane structures, but their refinement to differential nonabelian cohomology. See differential fivebrane structure.
fivebrane structure, differential fivebrane structure
|smooth ∞-group||Whitehead tower of smooth moduli ∞-stacks||G-structure/higher spin structure||obstruction|
|ninebrane 10-group||ninebrane structure||third fractional Pontryagin class|
|fivebrane 6-group||fivebrane structure||second fractional Pontryagin class|
|string 2-group||string structure||first fractional Pontryagin class|
|spin group||spin structure||second Stiefel-Whitney class|
|special orthogonal group||orientation structure||first Stiefel-Whitney class|
|orthogonal group||orthogonal structure/vielbein/Riemannian metric|
|general linear group||smooth manifold|
(all hooks are homotopy fiber sequences)
The notion was introduced in
It is briefly mentioned in
Related structures are also mentioned around p. 9 of
The differential refinement is discussed in
Articles that use Fivebrane structures include