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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.

76 votes
2 answers
9k views

Complex structure on $S^6$ gets published in Journ. Math. Phys

A paper by Gabor Etesi was published that purports to solve a major outstanding problem: Complex structure on the six dimensional sphere from a spontaneous symmetry breaking Journ. Math. Phys. 56, 04 …
Misha Verbitsky's user avatar
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
15 votes
3 answers
1k views

orbits of automorphism group for indefinite lattices

I have a question about indefinite lattices. QUESTION: Let $\Lambda\times\Lambda\rightarrow {\Bbb Z}$ be a lattice, that is, ${\Bbb Z}^n$ with a non-degenerate integer quadratic form, not necessarily …
Misha Verbitsky's user avatar
13 votes
1 answer
642 views

Does a resolution of a rational singularity have rationally connected fibers?

A rational singularity is a singularity of a complex variety $X$ such that for any resolution $\pi:\; \tilde X\rightarrow X$ the higher direct images $R^i\pi_*(O_{\tilde X})$ vanish for all $i>0$. Sup …
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
10 votes
3 answers
823 views

Newlander-Nirenberg in dimension 2

What is the easiest (and what is the most elementary) way of proving Newlander-Nirenberg theorem for Riemannian surfaces? I was able to reduce it to existence of non-trivial harmonic functions (locall …
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
2 answers
373 views

Real analytic subvariety in complex manifold which is complex outside of its singular set

Let $M$ be a complex manifold, and $Z \subset M$ a closed real analytic subvariety. Suppose that the set of smooth points in $Z$ is complex analytic in $M$. Will it follow that $Z$ is complex analytic …
Misha Verbitsky's user avatar

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