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Complex geometry is the study of complex manifolds, complex algebraic varieties, complex analytic spaces, and, by extension, of almost complex structures. It is a part of differential geometry, algebraic geometry and analytic geometry.

7 votes
Accepted

Existence of closed manifolds with more than 3 linearly independent complex structures?

A manifold admitting a triple of complex structures satisfying quaternionic relations also admits a torsion-free connection (called "Obata connection") preserving the quaternionic structure. Such a co …
Misha Verbitsky's user avatar
8 votes
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Does it make sense to define a holomorphic structure on $\mathbb{C}P^\infty$ and vector bund...

Yes, there is lots of literature on this subject. However, Tyurin proved that all vector bundles on $CP^\infty$ are direct sum of line bundles. There are several more recent papers by Penkov and Tikho …
Misha Verbitsky's user avatar
4 votes

Non Kähler blow-up of a Kähler manifold

When $Y$ is compact, the blow-up is always Kahler; see e.g. Lemma 3.4 in this paper (this is a generally known folklore theorem which we had to use, and hence written down). For $Y$ non-compact the …
Misha Verbitsky's user avatar
6 votes

Non projective hyperbolic compact complex space

The non-projective Kahler surfaces are either K3, tori or elliptic surfaces, known to be non-hyperbolic. Non-Kahler surfaces are either elliptic or class VII; the elliptic surfaces are obviously non-h …
Misha Verbitsky's user avatar
3 votes
Accepted

Nonpositive curvature of Stein manifolds

Complete, simply connected manifolds of non-positive sectional curvature are diffeomorphic to $R^n$, by Cartan-Hadamard theorem. Conversely, if it's $R^n$, you can put the metric of negative curvature …
Misha Verbitsky's user avatar
2 votes
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Intuition for holomorphic bisectional curvature

Ngaiming Mok, The uniformization theorem for compact Kähler manifolds of nonnegative holomorphic bisectional curvature, J. Differential Geom. Volume 27, Number 2 (1988), 179-214. Mok improves Mori's …
Misha Verbitsky's user avatar
8 votes
Accepted

What is the moduli of an algebraic torus

There is just no definition of the moduli for complex structures on non-compact manifolds, but by any reasonable definition, it would be (generally) very bad space, certainly infinite-dimensional. For …
Misha Verbitsky's user avatar
4 votes
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Kähler Identities: from the untwisted to the twisted case

The most clear proof (through differential operators, graded Jacobi identities and superalgebra) actually works in both twisted and untwisted cases, no need to derive one from another. See http://arxi …
Misha Verbitsky's user avatar
1 vote

Kahler structure on holomorphic principal bundles

A connected compact complex Lie group is a torus, hence the question is apparently about principal torus bundles. Of course, product of a torus and a compact Kahler manifold is Kahler, giving a trivia …
Misha Verbitsky's user avatar
25 votes
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Two definitions of Calabi-Yau manifolds

I have looked for a while for a proof which does not use the Calabi-Yau theorem and nobody seems to know it. Also, there are plenty of non-Kaehler manifolds with canonical bundle trivial topologicall …
Misha Verbitsky's user avatar
12 votes
Accepted

Deformations of Kähler manifolds where Hodge decomposition fails?

This is known, for projective (even Moishezon) manifolds as shown by Dan Popovici in his paper http://arxiv.org/abs/1003.3605 For general Kaehler manifold, this is conjectured. Popovici has proved t …
Misha Verbitsky's user avatar
6 votes

Question about Hodge number

For a Kaehler surface, the Hodge numbers are topological invariants. By Hodge Index Theorem, the signature of the Poincare pairing is equal to 2h^{2,0} +2 - h^{1,1}, hence h^{2,0} is a topological inv …
Misha Verbitsky's user avatar
0 votes

Examples of symplectic non-Kahler classes.

This is probably the simplest example. Take the Fubini-Study form $\omega$ on $CP^2$. Then $-\omega$ is symplectic, but never Kaehler, because by Yau's theorem $CP^2$ admits a unique (standard) comp …
Misha Verbitsky's user avatar
3 votes
Accepted

Global Definition of the Almost Complex Structure of a Complex Manifold

the construction of the canonical $J$ for a complex manifold is what I'm interested in Given a complex manifold, you have a bundle of (1,0)-forms within complexified 1-forms which is generated (o …
Misha Verbitsky's user avatar
9 votes
Accepted

Different occurences of the word 'period' in algebraic geometry

The second and the third are pretty much equivalent. Indeed, "the period" in XIX century sense is essentially the same as the discrepancy between the branches of a multi-valued function, obtained as a …
Misha Verbitsky's user avatar

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