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Revision as of 08:37, 28 January 2014 by en>David Eppstein (a little more context)
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In mathematics, a holomorphic vector bundle is a complex vector bundle over a complex manifold X such that the total space E is a complex manifold and the projection map π:EX is holomorphic. Fundamental examples are the holomorphic tangent bundle of a complex manifold, and its dual, the holomorphic cotangent bundle. A holomorphic line bundle is a rank one holomorphic vector bundle.

Definition through trivialization

Specifically, one requires that the trivialization maps

ϕU:π1(U)U×k

are biholomorphic maps. This is equivalent to requiring that the transition functions

tUV:UVGLk

are holomorphic maps. The holomorphic structure on the tangent bundle of a complex manifold is guaranteed by the remark that the derivative (in the appropriate sense) of a vector-valued holomorphic function is itself holomorphic.

The sheaf of holomorphic sections

Let E be a holomorphic vector bundle. A local section s:UE|U is said to be holomorphic if everywhere on U, it is holomorphic in some (equivalently any) trivialization.

This condition is local, so that holomorphic sections form a sheaf on X, sometimes denoted 𝒪(E). If E is the trivial line bundle _, then this sheaf coincides with the structure sheaf 𝒪X of the complex manifold X.

The sheaves of forms with values in a holomorphic vector bundle

If Xp,q denotes the sheaf of 𝒞 differential forms of type (p,q), then the sheaf p,q(E) of type (p,q) forms with values in E can be defined as the tensor product Xp,qE. These sheaves are fine, which means that it has partitions of the unity.

A fundamental distinction between smooth and holomorphic vector bundles is that in the latter, there is a canonical differential operator : the Dolbeault operator :p,q(E)p,q+1(E) obtained in trivializations.

Cohomology of holomorphic vector bundles

If E is a holomorphic vector bundle of rank r over X, one denotes 𝒪(E) the sheaf of holomorphic sections of E. Recall that it is a locally free sheaf of rank r over the structure sheaf 𝒪X of its base.

The cohomology of the vector bundle is then defined as the sheaf cohomology of 𝒪(E).

We have H0(X,𝒪(E))=Γ(X,𝒪(E)), the space of global holomorphic sections of E, whereas H1(X,𝒪(E)) parametrizes the group of extensions of the trivial line bundle of X by E, that is exact sequences of holomorphic vector bundles 0EFX×0. For the group structure, see also Baer sum.

The Picard group

In the context of complex differential geometry, the Picard group Pic(X) of the complex manifold X is the group of isomorphism classes of holomorphic line bundles with law the tensor product and inversion given by dualization.

It can be equivalently defined as the first cohomology group H1(X,𝒪X*) of the bundle of non-locally zero holomorphic functions.

References

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