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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.

57 votes

flatness in complex analytic geometry

Instead of trying to say what flatness in analytic geometry means I'll give you some street-fighting tricks for recognizing whether a morphism of analytic spaces ( not necessarily reduced) $f:X\to Y $ …
Georges Elencwajg's user avatar
43 votes

Simplest examples of nonisomorphic complex algebraic varieties with isomorphic analytifications

Dear Ravi, maybe the simplest example is one by Serre: the holomorphic Stein surface $\mathbb C^\ast\times \mathbb C^\ast $ underlies two non-isomorphic smooth complex algebraic varieties. 1) $\math …
Georges Elencwajg's user avatar
35 votes
Accepted

A geometric characterization for arithmetic genus

First let me note that there is an unfortunate clash in terminology: the arithmetic genus of a smooth complex projective variety $X$ of dimension $n$ can mean either a) The number $\chi (X, \mathca …
Georges Elencwajg's user avatar
17 votes
Accepted

Uniformization theorem in higher dimensions

There exist infinitely many holomorphically non-isomorphic complex structures on the unit ball of R^4 (or more generally R^2n): this is a beautiful theorem of Burns, Shnider, Wells ( Inventiones Math. …
Georges Elencwajg's user avatar
16 votes
3 answers
3k views

When is a holomorphic submersion with isomorphic fibers locally trivial?

A justly celebrated theorem by Ehresmann states that a proper smooth submersion $\pi: X\to S$ between smooth manifolds is locally trivial in the sense that every point $s\in S$ downstairs has a neigh …
Georges Elencwajg's user avatar
15 votes

Reference request: moduli spaces of vector bundles

Dear Mohammad, there is a rather elementary book Introduction to Moduli Problems and Orbit spaces by P.E. Newstead which will explain to you why stability is important, give you lots of examples (Ch …
Georges Elencwajg's user avatar
12 votes
Accepted

Most important domains, extension theorems, and functions in several complex variables

Here are a few points to guide you into the beautiful subject you had the good taste to choose. 1) Hartogs extension phenomenon :given two concentric balls in $ \mathbb C^n$, any holomorphic funct …
Georges Elencwajg's user avatar
11 votes
Accepted

Are spaces of holomorphic maps manifolds?

Let $X,Y$ be analytic spaces with $X$ compact reduced and $Y$ arbitrary (i.e. maybe with nilpotents in its structure sheaf). Then Douady showed in his thesis that the set of holomorphic maps $Hol(X,Y) …
Georges Elencwajg's user avatar
11 votes
Accepted

Explicit way to construct simple complex tori/abelian varieties of dimension at least 2

Recall that the Néron-Severi group of a complex manifold $X$ is the subgroup of $NS(X)\subset H^2(X, \mathbb Z) $ consisting of first Chern classes of holomorphic line bundles on $X$. More algebraical …
Georges Elencwajg's user avatar
10 votes

Connected complement manifold

Claim: The complement $U=\mathbb C^h\setminus \{F=0\}$ is path-connected and thus connected. Proof: Given $a,b\in U$ consider the affine complex line $L_{a,b}=L$ joining $a$ to $b$. The polynomial $ …
Georges Elencwajg's user avatar
7 votes

Complex geometry text/research introduction for the analyst

1) There is a great book From Holomorphic Functions to Complex Manifolds by Fritzsche-Grauert. It is very geometric and gives you the fundamentals on complex manifolds, including specialized topics, f …
Georges Elencwajg's user avatar
7 votes

Biholomorphism between neighborhood of a complex submanifold and a neighborhood of zero sect...

The answer is "no" because in general there does not even exist a neighbourhood $U$ of your submanifold that holomorphically retracts to the submanifold. In fact Finnur Lárusson has proved the followi …
Georges Elencwajg's user avatar
6 votes

Kähler metric on projectivised bundle

If $M$ is compact ( the usual assumption in Kähler manifold theory) the answer is "yes". You can look it up in Claire Voisin's book Proposition 3.18, page 78.
Georges Elencwajg's user avatar
5 votes

Are there compact analogues of Cartan's theorems A and B?

Dear Colin , for $X$ a holomorphic connected manifold, denote by $\mathcal M (X)$ its field of meromorphic functions. A) It is not true that a germ of holomorphic function $f_x\in \mathcal O_{X,x}$ …
Georges Elencwajg's user avatar
5 votes
Accepted

Density of holomorphic sections

Dear Benjamin, the statement that holomorphic sections are dense in the smooth sections is false, already for the trivial bundle of rank one $E_1=X\times \mathbb C$ over $X=\mathbb C$. Indeed on any …
Georges Elencwajg's user avatar

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