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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.

9 votes
1 answer
2k views

Deform a compact Kähler manifold to a non Kähler one

Could you give me an example of a compact Kähler manifold which analytically deforms to a non Kähler one? For example, there is no hope to find a complex structure on a Hopf manifold in order to make …
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  • 7,902
4 votes
5 answers
941 views

Uniformity of ampleness

Let $X$ be a smooth projective variety over $\mathbb C$ and $A\to X$ an ample line bundle. Is there an integer $k_0$ such that for all line bundle $L\to X$, the tensor product $A^{\otimes k}\otimes …
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  • 7,902
10 votes
1 answer
373 views

Non projective hyperbolic compact complex space

A famous conjecture by Kobayashi (perhaps slightly revisited subsequently) states that every compact hyperbolic Kähler manifold $X$ has ample canonical bundle. This implies in particular that $X$ is …
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  • 7,902
13 votes
1 answer
993 views

Examples of Brody hyperbolic affine varieties which are not Kobayashi hyperbolic

Let $X$ be a complex space. We say that $X$ is Brody hyperbolic if there is no non-constant holomorphic map $f\colon\mathbb C\to X$. We say that $X$ is Kobayashi hyperbolic if the Kobayashi pseudo …
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  • 7,902
12 votes
2 answers
2k views

Negative holomorphic sectional curvature

Let X be a complex hermitian manifold with hermitian form $\omega$. How can you prove that if $\omega$ has negative holomorphic sectional curvature, then its scalar curvature is negative, too?
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  • 7,902
11 votes
0 answers
200 views

Holomorphically convex manifolds and Bergman complete manifolds

Suppose $X$ is a complex manifold which admits the Bergman metric (for definitions, see for instance Kobayashi's book "Hyperbolic Complex Spaces"). Suppose moreover that the Bergman metric of $X$ is c …
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  • 7,902
2 votes
0 answers
224 views

Hermitian connections on real hypersurfaces of $\mathbb C^{n+1}$

I would like to find some non-trivial and "geometric" examples of hermitian connections (that is compatible with a give hermitian metric) on complex hermitian vector bundles over a smooth real manifol …
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  • 7,902
6 votes
1 answer
638 views

A line bundle not big but with good intersection numbers

Let $X$ be a complex projective manifold of complex dimension $n$ and $A\to X$ an ample line bundle. Let $L\to X$ be a line bundle such that $$ c_1(L)^k\cdot c_1(A)^{n-k}>0,\quad k=1,\dots,n. $$ Is it …
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  • 7,902
20 votes
1 answer
2k views

Rational or elliptic curves on Calabi-Yau threefolds

Let $X$ be a Calabi-Yau threefold. From a complex analytic point of view, it is widely believed that it should not be Kobayashi hyperbolic, that is it should always admit some non-constant entire map …
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  • 7,902
3 votes
2 answers
226 views

Uniformity of injectivity for maps associated to linear systems

Let $X$ be a compact complex manifold and $L\to X$ a holomorphic line bundle (without any a priori assumption on its positivity). Suppose that for each $x,y\in X$, with $x\ne y$, there exists a $k_0 …
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  • 7,902
10 votes
0 answers
515 views

About the Bloch conjecture on entire curves

The Bloch conjecture states the following: Bloch's conjecture. Let $X$ be a compact complex Kähler variety such that the irregularity $q = h^0(X,\Omega^1_X)$ is larger than the dimension $n = \dim X$ …
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  • 7,902
10 votes
0 answers
304 views

Examples of quasi-negative but not negative holomorphic sectional curvature

Let $(X,\omega)$ be a compact Kähler manifold and call $\operatorname{HSC}_{\omega}(x,[v])$ the holomorphic sectional curvature of the Chern connection of $\omega$ at the point $x\in X$ in the directi …
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  • 7,902
12 votes
0 answers
2k views

Dolbeault cohomology of complex tori.

Let $T=\mathbb C^n/\Lambda$ a complex torus. It is completely elementary to prove that the de Rham cohomology of $T$ in degree $q$ is isomorphic to the $q$-th exterior power of the dual of $\mathbb C^ …
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  • 7,902
10 votes
2 answers
591 views

Non-bimeromorphic compactifications

Let $X$ be a (smooth, non-compact) complex space. By a compactification of $X$ we mean a compact complex space $\overline X$ which contains a dense open subset biholomorphic to $X$ (we shall identify …
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  • 7,902
6 votes
1 answer
1k views

Blowing-up an ordinary double point, then contracting the exceptional locus to a curve

Let $X\subset\mathbb P^4$ a projective hypersurface with an ordinary double point at $o\in X$. Blow-up $\mathbb P^4$ at $o$ and let $E\simeq\mathbb P^3$ the exceptional divisor of this blow-up. Consi …
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