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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.

14 votes
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Variety without a compactification whose complement is smooth

Presumably, you want $\bar X$ to be smooth as well. Then there are many examples. Here is a simple one. Let $\bar Y$ be smooth projective curve of positive genus. Now remove at least two points to get …
Donu Arapura's user avatar
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6 votes
Accepted

Prefactor $2\pi i$ for Tate-Hodge structure

You are right that it is in some sense a matter of convention, but I claim it's a natural one. Perhaps the easiest example to explain is $H=H_1(X)$, where $X=\mathbb{C}^*$. By Deligne, this carries a …
Donu Arapura's user avatar
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7 votes

How does complex conjugation act on the Hodge filtration?

I thought it would be useful to give an explicit example to supplement Olivier Benoist's answer; I will use the same notation as in his answer. Let $f(x)\in \mathbb{R}[x]$ be cubic with distinct roo …
Donu Arapura's user avatar
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3 votes

The indecomposable bundle on an elliptic curve

I'll answer your main question for $r=1$, but for any smooth projective variety $X$. Interestingly, the answer is implicit in another paper of Atiyah's Complex analytic connections in fibre bundles, w …
Donu Arapura's user avatar
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5 votes

On Simpson's motivicity conjecture

In the 90's, Simpson proved that rigid local systems on a projective variety come from complex variations of Hodge structure, so it seemed a natural if bold leap to conjecture that they come from geo …
Donu Arapura's user avatar
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3 votes
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Cohomology of singular curves

You don't need all this machinery in this case (unless your goal was to understand the machinery). You have to exact sequences $$0\to W_0\to H^1(X) \to H^1(Y)\to 0$$ $$0 \to H^1(X')\to H^1(Y)\to \oplu …
Donu Arapura's user avatar
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3 votes

Motivation behind spectral sequences

I suspect a previous comment of mine led to this question, so let me say a few words here. The basic problem is this: Suppose $(A^\bullet, F)$ is a filtered complex, then one wants to relate the (co …
Donu Arapura's user avatar
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4 votes
Accepted

What does does the monodromy weight filtration represent?

Given a nilpotent endomorphism $N$ of a finite dimension vector space $V$, Jordan canonical form implies that we can decomponse $V$ into a sum of "blocks" on which we can find bases satisfying $Ne_1 = …
Donu Arapura's user avatar
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4 votes
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Meaning of torsion points in a Roitman's theorem

It occurs to me that your question shouldn't be taken literally, and is simply asking about the meaning of the theorem. To appreciate it, one can ask what $CH_0(X)$ looks like. As a first attempt, ma …
Donu Arapura's user avatar
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5 votes
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Relating the holomorphic Euler characteristic of a family of algebraic varieties to properti...

I'm not entirely sure what would constitute an answer. But here a few simple observations. Let me focus on what you seem be interested in, namely a projective family of connected curves over smooth p …
Donu Arapura's user avatar
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8 votes
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Do we have the Oka coherence theorem for finite group actions?

This would be true. You need two facts: Grauert's theorem that coherent sheaves are preserved by proper direct images. This implies $\pi_*\mathcal{O}_{\mathbb{C}^n}$ is coherent. Sub modules of cohe …
Donu Arapura's user avatar
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6 votes

Gorenstein varieties: why the two definitions are equivalent?

I would say that definition of Gorenstein given in Hartshorne etc. is the correct one; it certainly doesn't require normality. For example, a singular plane curve is Gorenstein in this sense, but not …
Donu Arapura's user avatar
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2 votes

Extension of closed $(1, 1)$-forms

Contrary to my earlier comments, I now believe (but I haven't completely checked) that this is false in general. (I prefer not to comment on the paper you linked.) Suppose that $X$ is a Kähler manifol …
Donu Arapura's user avatar
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1 vote
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Period map for $\partial\bar\partial$-manifolds

Let me start with a disclaimer that I think the following facts are true, but I'm doing this over coffee and I haven't checked the details carefully. First, I'll redefine $F^pH^k(X,\mathbb{C})$ to be …
Donu Arapura's user avatar
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7 votes
Accepted

Comparison of weight filtration on cohomology of complex manifold

Yes, the $\ell$-adic weight filtration is compatible with the weight filtration in mixed Hodge theory under the comparison isomorphism. These facts go back to Deligne, and are described in his announc …
Donu Arapura's user avatar
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