# Fibered manifold

(Redirected from Fibred manifold)

In differential geometry, in the category of differentiable manifolds, a fibered manifold is a surjective submersion[1]

${\displaystyle \pi \colon E\to B\,}$

i.e. a surjective differentiable mapping such that at each point yE the tangent mapping

${\displaystyle T_{y}\pi \colon T_{y}E\to T_{\pi (y)}B}$

is surjective, or, equivalently, its rank equals dim B.

## History

In topology, the words fiber (Faser in German) and fiber space (gefaserter Raum) appeared for the first time in a paper by Seifert in 1932,[2] but his definitions are limited to a very special case. The main difference from the present day conception of a fiber space, however, was that for Seifert what is now called the base space (topological space) of a fiber (topological) space E was not part of the structure, but derived from it as a quotient space of E. The first definition of fiber space is given by Hassler Whitney in 1935 [3] under the name sphere space, but in 1940 Whitney changed the name to sphere bundle.[4]

The theory of fibered spaces, of which vector bundles, principal bundles, topological fibrations and fibered manifolds are a special case, is attributed to Seifert, Hopf, Feldbau,[5] Whitney, Steenrod, Ehresmann,[6][7][8] Serre,[9] and others.

## Formal definition

A triple (E, π, B) where E and B are differentiable manifolds and π: EB is a surjective submersion, is called a fibered manifold.[10] E is called the total space, B is called the base.

## Examples

• Every differentiable fiber bundle is a fibered manifold.
• Every differentiable covering space is a fibered manifold with discrete fiber.
• In general, a fibered manifold needs not to be a fiber bundle: different fibers may have different topologies. An example of this phenomenon may be constructed by taking the trivial bundle (S1 × ℝ, π1, S1) and deleting two points in to two different fibers over the base manifold S1.The result is a new fibered manifold where all the fibers except two are connected.

## Properties

• Any surjective submersion π: EB is open: for each open VE, the set π(V) ⊂ B is open in B.
• Each fiber π−1(b) ⊂ E, bB is a closed embedded submanifold of E of dimension dim E − dim B.[11]
• A fibered manifold admits local sections: For each yE there is an open neighborhood U of π(y) in B and a smooth mapping s: UE with πs = IdU and s(π(y)) = y.
• A surjection π : EB is a fibered manifold if and only if there exists a local section s : BE of π (with πs = IdB) passing through each yE.[12]

## Fibered coordinates

Let B (resp. E) be an n-dimensional (resp. p-dimensional) manifold. A fibered manifold (E, π, B) admits fiber charts. We say that a chart (V, ψ) on E is a fiber chart, or is adapted to the surjective submersion π: EB if there exists a chart (U, φ) on B such that U = π(V) and

${\displaystyle u^{1}=x^{1}\circ \pi ,\,u^{2}=x^{2}\circ \pi ,\,\dots ,\,u^{n}=x^{n}\circ \pi \,,}$

where

{\displaystyle {\begin{aligned}\psi &=(u^{1},\dots ,u^{n},y^{1},\dots ,y^{p-n}).\quad y_{0}\in V,\\\varphi &=(x^{1},\dots ,x^{n}),\quad \pi (y_{0})\in U.\end{aligned}}}

The above fiber chart condition may be equivalently expressed by

${\displaystyle \varphi \circ \pi =\mathrm {pr} _{1}\circ \psi ,}$

where

${\displaystyle {\mathrm {pr} _{1}}\colon {\mathbb {R} ^{n}}\times {\mathbb {R} ^{p-n}}\to {\mathbb {R} ^{n}}\,}$

is the projection onto the first n coordinates. The chart (U, φ) is then obviously unique. In view of the above property, the fibered coordinates of a fiber chart (V, ψ) are usually denoted by ψ = (xi, yσ) where i ∈ {1, ..., n}, σ ∈ {1, ..., m}, m = pn the coordinates of the corresponding chart U, φ) on B are then denoted, with the obvious convention, by φ = (xi) where i ∈ {1, ..., n}.

Conversely, if a surjection π: EB admits a fibered atlas, then π: EB is a fibered manifold.

## Local trivialization and fiber bundles

Let EB be a fibered manifold and V any manifold. Then an open covering {Uα} of B together with maps[13]

${\displaystyle \psi :\pi ^{-1}(U_{\alpha })\rightarrow U_{\alpha }\times V,}$

called trivialization maps, such that

${\displaystyle \mathrm {pr} _{1}\circ \psi _{\alpha }=\pi ,\forall \alpha }$

is a local trivialization with respect to V.

A fibered manifold together with a manifold V is a fiber bundle with typical fiber (or just fiber) V if it admits a local trivialization with respect to V. The atlas Ψ = {(Uα, ψα)} is then called a bundle atlas.

## References

### Historical

• Ehresmann, C. (1947a). "Sur la théorie des espaces fibrés". Coll. Top. alg. Paris (in French). C.N.R.S.: 3–15.
• Ehresmann, C. (1947b). "Sur les espaces fibrés différentiables". C. R. Acad. Sci. Paris (in French). 224: 1611–1612.
• Ehresmann, C. (1955). "Les prolongements d'un espace fibré différentiable". C. R. Acad. Sci. Paris (in French). 240: 1755–1757.
• Feldbau, J. (1939). "Sur la classification des espaces fibrés". C. R. Acad. Sci. Paris (in French). 208: 1621–1623.
• Seifert, H. (1932). "Topologie dreidimensionaler geschlossener Räume". Acta Math. (in French). 60: 147–238. doi:10.1007/bf02398271.
• Serre, J.-P. (1951). "Homologie singulière des espaces fibrés. Applications". Ann. of Math. (in French). 54: 425–505. doi:10.2307/1969485.
• Whitney, H. (1935). "Sphere spaces". Proc. Natl. Acad. Sci. USA. 21: 464–468. (open access)
• Whitney, H. (1940). "On the theory of sphere bundles". Proc. Natl. Acad. Sci. USA. 26: 148–153. MR 0001338. (open access)