Natural bundle
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In differential geometry, a field in mathematics, a natural bundle is any fiber bundle associated to the s-frame bundle for some . It turns out that its transition functions depend functionally on local changes of coordinates in the base manifold together with their partial derivatives up to order at most .[1]
The concept of a natural bundle was introduced by Albert Nijenhuis as a modern reformulation of the classical concept of an arbitrary bundle of geometric objects.[2]
Definition
Let denote the category of smooth manifolds and smooth maps and the category of smooth -dimensional manifolds and local diffeomorphisms. Consider also the category of fibred manifolds and bundle morphisms, and the functor associating to any fibred manifold its base manifold.
A natural bundle (or bundle functor) is a functor satisfying the following three properties:
- , i.e. is a fibred manifold over , with projection denoted by ;
- if is an open submanifold, with inclusion map , then coincides with , and is the inclusion ;
- for any smooth map such that is a local diffeomorphism for every , then the function is smooth.
As a consequence of the first condition, one has a natural transformation .
Finite order natural bundles
Summarize
Perspective
A natural bundle is called of finite order if, for every local diffeomorphism and every point , the map depends only on the jet . Equivalently, for every local diffeomorphisms and every point , one hasNatural bundles of order coincide with the associated fibre bundles to the -th order frame bundles .
A classical result by Epstein and Thurston shows that all natural bundles have finite order.[3]
Examples
An example of natural bundle (of first order) is the tangent bundle of a manifold .
Other examples include the cotangent bundles, the bundles of metrics of signature and the bundle of linear connections.[4]
Notes
References
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