Normal bundle

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In differential geometry, a field of mathematics, a normal bundle is a particular kind of vector bundle.

[edit] Definition

Let (M,g) be a Riemannian manifold, and S \subset M a Riemannian submanifold. Define, for a given p \in S, a vector n \in \mathrm{T}_p M to be normal to S whenever g(n,v) = 0 for all v\in \mathrm{T}_p S (so that n is orthogonal to TpS). The set NpS of all such n is then called the normal space to S at p.

Just as the total space of the tangent bundle to a manifold is constructed from all tangent spaces to the manifold, the total space of the normal bundle NS to S is defined as

\mathrm{N}S := \coprod_{p \in S} \mathrm{N}_p S.

The conormal bundle is defined as the dual bundle to the normal bundle. It can be realised naturally as a sub-bundle of the cotangent bundle.

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