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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.

25 votes
Accepted

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
20 votes
Accepted

Which almost complex manifolds admit a complex structure?

In complex dimension 3 or more it is still an open conjecture (which was re-stated Yau a couple of years ago in his UCLA lectures). There is not a single known example of an almost complex manifold of …
Misha Verbitsky's user avatar
19 votes
Accepted

Three-dimensional compact Kähler manifolds

The main obstruction to existence of Kahler metric (in addition to Lefschetz SL(2)-action and Riemann-Hodge relations in cohomology) is homotopy formality: the cohomology ring of a Kahler manifold is …
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
12 votes
Accepted

Is the deformation limit of Ricci-flat Kahler manifolds Kahler?

There are counterexamples: a Moishezon manifold, which has trivial canonical class and is birationally equivalent to a hyperkahler manifold, is also deformationally equivalent to a hyperkaehler manif …
Misha Verbitsky's user avatar
11 votes

Weitzenböck Identities

The most general version of Weitzenbock identities (with coefficients in appropriate universal enveloping algebras) is due to Uwe Semmelmann and Gregor Weingart: http://arxiv.org/abs/math/0702031 "The …
Misha Verbitsky's user avatar
10 votes

How restrictive is having zero Chern numbers for a compact complex manifold ? Same for negat...

When a compact Kahler manifold satisfies $c_1=0$, it admits a Ricci-flat Kahler metric by Calabi-Yau, hence its tangent bundle is polystable (direct sum of stable bundles of the same slope). Then its …
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
8 votes
Accepted

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
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
8 votes

Coincide between Chern-connection and Levi-Civita connection

It is easier to prove this result for 1-forms, instead of vector fields. On (1,0)-forms, $\nabla^{0,1}=\bar\partial$ because the Levi-Civita connection is torsion-free, hence $\bigwedge(\nabla(\eta))= …
Misha Verbitsky's user avatar
8 votes
Accepted

Proper family deformation retracts onto special fiber

Here is the reference: Persson, Ulf, On degenerations of algebraic surfaces, Mem. Amer. Math. Soc. 11 (1977), no. 189. Clemens, C. H. Degeneration of Kähler manifolds. Duke Math. J. 44 (1977), no. …
Misha Verbitsky's user avatar
7 votes
Accepted

Finiteness of De Rham cohomology of smooth quasi-projective varieties

I think there are proofs which are much easier. For example, you can try to compute the cohomology using the Morse theory. For that you need existence of Morse functions having finitely many critical …
Misha Verbitsky's user avatar
7 votes
Accepted

"Simple" Kahler manifolds

A generic deformation of a Hilbert scheme of K3 and a generic torus have no subvarieties, hence they are "simple" in the above sense. For a torus it's well known, for a Hilbert scheme of K3 it's in my …
Misha Verbitsky's user avatar
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

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