vector bundle, 2-vector bundle, (∞,1)-vector bundle
real, complex/holomorphic, quaternionic
group cohomology, nonabelian group cohomology, Lie group cohomology
cohomology with constant coefficients / with a local system of coefficients
differential cohomology
A fibre bundle or fiber bundle is a bundle in which every fibre is isomorphic, in some coherent way, to a standard fibre or typical fiber. Usually one also requires that it be locally trivial, hence locally of the form of a Cartesian product with that typical fiber.
In the most general sense, a bundle over an object in a category is a morphism in .
In appropriate contexts, a fibre bundle over with standard fibre may be defined as a bundle over such that, given any global element , the pullback of along is isomorphic to . Certainly this definition is appropriate whenever has a terminal object which is a separator, as in a well-pointed category; even then, however, one often wants the more restrictive notion below.
One often writes a typical fibre bundle in shorthand as or
even though there is not a single morphism but instead one for each global element (and none at all if has no global elements!).
If is a site, then a locally trivial fibre bundle over with typical fibre is a bundle over with a cover such that, for each index , the pullback of along is isomorphic in the slice category to the trivial bundle (a local trivialization).
One can also drop and define a slightly more general notion of locally trivial bundle over as a bundle over with a cover such that, for each index , there is a fibre and an isomorphism in between the pullback and the trivial bundle . Every locally trivial fibre bundle is obviously a locally trivial bundle; the converse holds if is connected.
Now suppose that is a fibre bundle over with typical fibre , locally trivialised over an (open) cover via isomorphisms . Given an index and an index , let be the fibred product (pullback) of and . Note that we can pull back the commutative triangle formed by along to get a new isomorphism :
We can do the same on the other side, leading to the following situation:
Then we have an automorphism of in given by . The are the transition morphisms of the locally trivial fibre bundle .
If in fact admits a global trivialisation , then one can see that the two isomorphisms and are equal to the pullback of (the commutative triangle formed by) along , so that the transition morphisms are all identities.
Often one considers special kinds of bundles, by requiring structure on the standard fibre and/or conditions on the transition morphisms . For example:
If is a group object in that acts on , then a -bundle (or bundle with structure group ) over with standard fibre is a locally trivial fibre bundle over with standard fibre together with morphisms that, relative to the action of on , give the transition maps . (The morphism is also written , conflating action with application.)
More specifically, a (right or left) principal -bundle over is a -bundle over with standard fibre , associated with the action of on itself by (right or left) multiplication.
If is an object of a concrete category over , then we can consider locally trivial fibre bundles with standard fibre such that the transition morphisms are structure-preserving morphisms. If the automorphism group can be internalised in , then this the same as an -bundle, but the concept makes sense in any case.
As a fairly specific example, if is a topological vector space (and is a category with structure to support this, such as Top or Diff), then a vector bundle over with standard fibre is a -bundle over with standard fibre , where is the general linear group with its defining action on .
Given a right principal -bundle and a left -space , all in a sufficiently strong category (such as Top), one can form the quotient object , where is a product and is the smallest congruence such that (using generalized elements) ; there is a canonical projection where the class of is mapped to , hence making into a fibre bundle with typical fiber , and the transition functions belonging to the action of on . We say that is the associated bundle to with fiber .
In higher category theory the notion of fiber bundle generalizes. See
Under the interpretation of modules as generalized vector bundles, locally trivial fiber bundles correspond to locally free modules. See there for more.
In noncommutative geometry both principal and associated bundles have analogues. The principal bundles over noncommutative spaces typically have structure group replaced by a Hopf algebra; the most well-known class whose base is described by a single algebra are Hopf–Galois extensions; the global sections of the associated bundle are formed using cotensor product. Transition functions can be to some extent emulated using noncommutative localizations, which yield nonaffine generalizations of Hopf–Galois extensions. Another generalization is when Hopf–Galois extensions in the sense of comodule algebras are replaced by entwining structures with analogous Galois condition.
Every locally trivial topological fiber bundle projection is a Serre fibration, and a Hurewicz fibration if it is also a numerable bundle.
It is clear that the projection out of a Cartesian product is a Serre fibration. With this, the statement follows from local triviality and the local recognition of Serre fibrations (this Prop) and of Hurewicz fibrations (this Prop.), respectively.
Beware that the converse statement is far from being true.
fiber bundle / fiber ∞-bundle
principal bundle / torsor / associated bundle
Fiber bundles (then spelled fibre-bundles) were originally defined in:
Hassler Whitney, On the theory of sphere-bundles, Proceedings of the National Academy of Sciences 26 2 (1940) 148-153 [doi:10.1073/pnas.26.2.148]
(with focus on sphere bundles)
Other sources:
Norman Steenrod, Section I.7 of The topology of fibre bundles, Princeton Mathematical Series 14, Princeton Univ. Press (1951) [jstor:j.ctt1bpm9t5]
Alexander Grothendieck, A General Theory of Fibre Spaces With Structure Sheaf, University of Kansas, Report No. 4 (1955, 1958) [pdf, pdf]
(in relation to nonabelian Čech cohomology)
Jean Frenkel, Cohomologie non abélienne et espaces fibrés, Bulletin de la Société Mathématique de France, 85 (1957) 135-220 [numdam:BSMF_1957__85__135_0]
Glen Bredon, Section II.1 of: Introduction to compact transformation groups, Academic Press 1972 (ISBN:9780080873596, pdf)
Dale Husemöller, Fibre bundles, McGraw-Hill 1966 (300 p.); Springer Graduate Texts in Math. 20, 2nd ed. 1975 (327 p.), 3rd. ed. 1994 (353 p.) (pdf)
Dale Husemoeller, Michael Joachim, Branislav Jurčo, Martin Schottenloher, Basic Bundle Theory and K-Cohomology Invariants,
Lecture Notes in Physics, Springer 2008 (pdf)
Ralph Cohen, The Topology of Fiber Bundles, Stanford University (2017) (pdf, OMN:201707.110706)
Dai Tamaki, Fiber Bundles and Homotopy, World Scientific 2021 (doi:10.1142/12308)
(in the context of homotopy theory)
With an eye towards application in mathematical physics:
Mikio Nakahara, Chapter 9 of: Geometry, Topology and Physics, IOP 2003 (doi:10.1201/9781315275826, pdf)
Gerd Rudolph, Matthias Schmidt, Chapter 1 of: Differential Geometry and Mathematical Physics Part II. Fibre Bundles, Topology and Gauge Fields, Springer 2017 (doi:10.1007/978-94-024-0959-8)
Discussion of fiber bundles internal to finitely complete categories:
Anders Kock, Fibre bundles in general categories, Journal of Pure and Applied Algebra 56 3 (1989) 233-245 [doi:10.1016/0022-4049(89)90059-5]
Anders Kock, Generalized fibre bundles, in: Categorical Algebra and its Applications, Lecture Notes in Mathematics 1348 (2006) 194-207 [doi:10.1007/BFb0081359]
Last revised on February 3, 2024 at 03:52:42. See the history of this page for a list of all contributions to it.