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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.
41
votes
Accepted
de Rham vs Dolbeault Cohomology
Let $\Omega^{p,q}(M)$ be the $C^{\infty}$ $(p,q)$-forms. One always has a double complex with $\Omega^{p,q}(M)$ in position $(p,q)$. The cohomology in the $q$ direction is Dolbeault cohomology, the co …
22
votes
Accepted
Are all holomorphic vector bundles on a contractible complex manifold trivial?
No, even for line bundles. We have the short exact sequence of sheaves
$$0 \to \underline{\mathbb{Z}} \overset{2 \pi i}{\longrightarrow} \mathcal{O} \overset{\exp}{\longrightarrow} \mathcal{O}^{\ast} …
19
votes
Accepted
Intuitive Aproach to Dolbeault Cohomology
Here is some nonsense that I find useful: On a complex manifold,
$$\frac{\mbox{locally constant functions}}{\mbox{smooth functions}} \approx \frac{\mbox{locally constant functions}}{\mbox{holomorphic …
18
votes
Accepted
$\partial \bar{\partial}$ lemma for contractible domains
Okay, here is a counter-example. Let $X$ be the following open subset of $\mathbb{C}^2$:
$$X:= \{ (z_1, z_2) : |z_1| < 2,\ |z_2| < 1 \} \cup \{(z_1, z_2): |z_1| < 1,\ |z_2| < 2 \}$$
This is the stand …
17
votes
Examples of smooth manifolds admitting inbetween one and a continuum of complex structures
There are countably many complex structures on $S^2 \times S^2$ up to isomorphism. Specifically, the even Hirzebruch surfaces $F_{2k}$ are the only options. This is the main result of
Qin, Zhenbo, C …
15
votes
Accepted
A topological consequence of Riemann-Roch in the almost complex case
I believe that the displayed equation is valid for almost complex manifolds. This is closely related to a computation I talked about here.
Let $r_1$, $r_2$, ..., $r_n$ be the chern roots of the tange …
15
votes
Accepted
Relation between the cohomology group of a curve and the cohomology group of its jacobian
$\def\Alb{\text{Alb}}\def\Pic{\text{Pic}}\def\CC{\mathbb{C}}\def\ZZ{\mathbb{Z}}\def\RR{\mathbb{R}}\def\cO{\mathcal{O}}$There are two abelian varieties associated to a smooth projective connected $n$-f …
14
votes
Accepted
Algebraic de Rham cohomology vs. analytic de Rham cohomology
I don't think you can get this directly from GAGA. The reference that I know for this result is Grothendieck, On the de Rham cohomology of algebraic varieties. It is short, beautiful, and in English.
13
votes
Accepted
Understanding the Hodge filtration
The naive Hodge filtration of a smooth affine variety is, indeed, the whole thing. We always have the short exact sequence of complexes:
$$0 \to \Omega^{\bullet, \geq p} \to \Omega^{\bullet} \to \Omeg …
13
votes
Accepted
Hard Lefschetz Theorem for the Flag Manifolds
I'll spell out Hard Lefschetz as an explicit combinatorial statement about the Grassmannian $G(d,n)$. I can definitely give you a version of this for the full flag manifold if you want it and probably …
12
votes
Accepted
Nonalgebraic complex manifolds
I wrote a blog post about some of the standard examples of nonalgebraic compact complex manifolds.
10
votes
Why are local systems on a complex analytic space equivalent to vector bundles with flat con...
You might also want to read Carlos Simpson's paper "Moduli of representations of the fundamental group of a smooth projective variety", parts I and II. He explains in great detail how to make the set …
10
votes
The Construction of a Basis of Holomorphic Differential 1-forms for a given Planar Curve
$\def\CC{\mathbb{C}}$I'll come back later and leave an answer to (1), which is classical and straightforward. I have nothing to say about (3). I thought the most interesting question was (2), but I am …
10
votes
Converses to Cartan's Theorem B
For (4), there are finite CW complexes $X$ which are not contractible, but such that $H^q(X, \mathcal{F})$ vanishes for all (finite rank) locally constant sheaves $\mathcal{F}$. Specifically, take $X$ …
10
votes
Accepted
The Construction of a Basis of Holomorphic Differential 1-forms for a given Planar Curve
I'm getting back to the question of describing holomorphic $1$-forms on a plane curve.
Affine curves: Let $X$ be a smooth curve in $\mathbb{A}^2$, given by the equation $F(x,y)$. Then $F_x dx + F_y …