# nLab holomorphic vector bundle

Contents

### Context

#### Bundles

bundles

fiber bundles in physics

complex geometry

# Contents

## Idea

A holomorphic vector bundle is a complex vector bundle over a complex manifold such that it admits transition functions that are holomorphic functions.

## Properties

### As complex algebraic vector bundles

By the GAGA-principle, holomorphic vector bundles and more generally analytic coherent sheaves over a projective smooth complex variety coincide with complex algebraic vector bundles/coherent sheaves.

### As complex vector bundles with holomorphically flat connection

###### Theorem

(Koszul-Malgrange theorem)

Holomorphic vector bundles over a complex manifold are equivalently complex vector bundles which are equipped with a holomorphically flat connection (hence a connection whose holomorphic component vanishes). Under this identification the Dolbeault operator $\bar \partial$ acting on the sections of the holomorphic vector bundle is identified with the holomorphic component of the covariant derivative of the given connection.

The analogous statement is true for generalization of vector bundles to chain complexes of module sheaves with coherent cohomology.

For complex vector bundles over complex varieties this statement is due to Alexander Grothendieck and (Koszul-Malgrange 58), recalled for instance as (Pali 06, theorem 1). It may be understood as a special case of the Newlander-Nirenberg theorem, see (Delzant-Py 10, section 6), which also generalises the proof to infinite-dimensional vector bundles. Over Riemann surfaces, see below, the statement was highlighted in (Atiyah-Bott 83) in the context of the Narasimhan-Seshadri theorem.

The generalization from vector bundles to coherent sheaves is due to (Pali 06). In the genrality of (∞,1)-categories of chain complexes (dg-categories) of holomorphic vector bundles the statement is discussed in (Block 05).

###### Remark

The equivalence in theorem serves to relate a fair bit of differential geometry/differential cohomology with constructions in algebraic geometry. For instance intermediate Jacobians arise in differential geometry and quantum field theory as moduli spaces of flat connections equipped with symplectic structure and Kähler polarization, all of which in terms of algebraic geometry directly comes down moduli spaces of abelian sheaf cohomology with coefficients in the structure sheaf (and/or some variants of that, under the exponential exact sequence).

### Over Riemann surfaces

Over Riemann surfaces holomorphic vector bundles are a central part of the theory of the moduli space of flat connections. See at Narasimhan-Seshadri theorem.

A key observation here is (Atiyah-Bott 83, section 7), that a $U(n)$-principal connection induces a holomorphic structure on the associated complex vector bundle by taking the $(0,1)$-part of the connection 1-form as the Dolbeault operator. For review of the statement and its proof see (Evans, lecture 10).

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### General

Textbook accounts:

### Relation to complex vector bundles with flat holomorphic connection

The classical statement of theorem is due to Alexander Grothendieck and

Over Riemann surfaces and in the context of the moduli space of flat connections:

Generalization to coherent sheaves is due to

• N. Pali, Faisceaux $\bar \partial$-cohrents sur les variété complexes ( $\bar \partial$-Coherent sheaves on complex manifolds) Math. Ann. 336 (2006), no. 3, 571–615 (arXiv:math/0305422)

Further Generalization to chain complexes of holomorphic vector bundles is discussed in

in terms of Lie infinity-algebroid representations of the holomorphic tangent Lie algebroid.

Generalization to infinite-dimensional vector bundles is in

• Thomas Delzant, Pierre Py, Kähler groups, real hyperbolic spaces and the Cremona group, Compositio Math. 148, no. 1 (2012), 153–184 (arXiv:1012.1585)
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