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Questions about Kähler manifolds and Kähler metrics.

8 votes
Accepted

Kleiman criterion for Kähler classes

This is false. There exists a smooth projective surface $X$ with a strictly nef divisor $D$ (so $D\cdot C>0$ for all curves $C\subset X$) and yet $(D^2)=0$, so in particular $D$ is not ample, see e.g. …
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2 votes

Are holomorphic quasi-positive line bundles on a Kähler manifold positive?

Take $X$ any smooth projective variety of dimension at least $2$, let $H$ be an ample (i.e. positive) line bundle on $X$, let $\pi:Y\to X$ be the blow-up of a point in $X$ and let $L=\pi^*H$. Then $L$ …
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4 votes

Inequality on Kähler classes

It is a consequence of the Khovanskii-Teissier inequality for Kähler classes (which was proved by Gromov and Demailly on Kähler manifolds, the algebraic case is also in Lazarsfeld's book): $$\int_X \ …
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7 votes
Accepted

Kahler manifolds with constant bisectional curvature

This is theorem 7.9 in the book of Kobayashi-Nomizu "Foundations of Differential Geometry Vol.II". There the authors attribute it to Hawley and Igusa independently. These are probably the first papers …
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24 votes
Accepted

On compact Kähler manifold diffeomorphic to complex projective space

The case when $n$ is even has been famously ruled out by Yau as a consequence of his proof of the Calabi Conjecture, see his original paper or these notes. In fact, thanks to results of Novikov, you …
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7 votes
Accepted

Where do the Kähler Identities first appear?

As you hinted yourself, they were indeed discovered by W.V.D. Hodge. They appear explicitly in his 1941 book "The Theory and Applications of Harmonic Integrals", which you can find here, see e.g. the …
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6 votes
Accepted

A question about the existence of a constant scalar curvature metric on $\mathbb{C}P^n\#\ove...

There are no constant scalar curvature Kähler metrics on $M$, the blowup of $\mathbb{CP}^n$ at one point in any Kähler class and for any $n>1$. This is because of the Lichnerowicz-Matsushima obstruc …
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1 vote

the existence of compact Kahler manifolds satisfying some Hodge numbers' restrictions

EDIT: this answer refers to a previous version of the question. Already for $n=3$ the answer is no. Indeed, $h^{3,3}=1$ so by your condition $h^{1,1}=h^{2,2}=0$ but a compact Kähler manifold has $h^{ …
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2 votes
Accepted

Varying a Kahler metric in a neighborhood of a point

This is not literally the answer that the OP wanted (a reference to the literature, which I am not aware of), but following the comments above let me write down the simple gluing argument. Let $\wide …
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4 votes
Accepted

Rationally connected Kähler manifolds are projective

This result follows from Corollaire (p.212) of this paper by F. Campana, Coréduction algébrique d'un espace analytique faiblement kählérien compact, Invent. Math. 63 (1981), no. 2, 187–223. I had the …
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2 votes
Accepted

Can a real (1,1) form $\phi$ be represented by $u\sqrt{-1}\partial\bar{\partial}u$ on a Kähl...

If $M$ is compact this is obviously false: if we can write $\phi=u\sqrt{-1}\partial\overline{\partial}u$ then $\int_M \omega\wedge\phi\leq 0$ integrating by parts. So for every $\phi$ which does not s …
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6 votes
Accepted

An integration identity on $\mathbb{P}^{n-1}$

If I remember correctly, you can find this in the book "Complex Differential Geometry" by Fangyang Zheng in Chapter 7. The analogous result "with real coefficients" (i.e. for real vectors and with $S^ …
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14 votes
Accepted

Does equality of Laplacians imply Kähler?

The answer is yes, as proved by Y. Ogawa in this paper, see Theorem 3.10. Apparently equality on functions and $1$-forms is enough to conclude that the metric is Kähler. There is also a related paper …
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4 votes

"Simple" Kahler manifolds

These manifolds have actually been studied to some extent by Campana and Peternell in their series of papers "Towards a Mori theory on compact Kähler threefolds I, II, III". In those papers they menti …
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6 votes
Accepted

A conjecture from Jean Varouchas on Kahler varieties

This problem was solved by Barlet and Varouchas in this paper. The base $X'$ is assumed to be reduced (surely this is OK for you), and the fibers pure dimensional (also certainly acceptable).
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