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Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.

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?
7 votes

Hom between Brody hyperbolic varieties

I assume that for $\operatorname{Hom}(X,Y)$ you mean $\operatorname{Hol}(X,Y)$, that is the family of all holomorphic maps from $X$ to $Y$, endowed with its universal complex structure (which exists s …
diverietti's user avatar
  • 7,902
27 votes
Accepted

Is the complex structure of $\mathbb CP^n$ unique?

Let me write this too long comment as an answer. As abx says, what we do know is Theorem 1. If a Kähler manifold $X$ is homeomorphic to $\mathbb{CP}^n$, then $X$ is biholomorphic to it. This is due to …
diverietti's user avatar
  • 7,902
22 votes
1 answer
1k views

Relationship between the signs of different notions of curvature in complex geometry

Let $(X,\omega)$ be a complex hermitian manifold, and call $\Theta$ its Chern curvature tensor. Out of this we can consider different notions of curvature, namely the holomorphic bisectional curvature …
5 votes
Accepted

Existence of a connection $A$ on a holomorphic line bundle $L$, s.t $F(A)=(\deg L)\omega$

Let me expand a bit Henri's (hi Henri!) answer, even if this is completely standard. In general, given a compact Kähler manifold $X$ of any dimension, given a holomorphic line bundle $L\to X$, and giv …
diverietti's user avatar
  • 7,902
2 votes

Examples of surfaces with negative Kahler curvature operator

Examples of compact Kähler manifolds with non positive holomorphic bisectional curvature are given by: Closed submanifolds of complex tori. Smooth compact quotients of bounded symmetric domains. M …
diverietti's user avatar
  • 7,902
7 votes

Griffiths-positive metric

As soon as the base manifold has dimension greater than one, the existence of Griffiths positive metrics on an ample vector bundle is not known (and even in the one dimensional case, it is not obvious …
Ben McKay's user avatar
  • 26.3k
0 votes

A question about nef classes on compact Kähler manifolds

Just for fun, here is an answer in the purely algebraic setting. So, suppose that $X$ is irreducible projective algebraic of dimension $n$, $\alpha=c_1(\mathcal O_X(D))$ is the class of a nef diviso …
diverietti's user avatar
  • 7,902
5 votes

Is hyperbolicity a Zariski open condition?

Kobayashi hyperbolicity (or Brody hyperbolicity, the two notions coincide for compact complex spaces), is an open condition with respect to the analytic topology. Thus, for instance, once you find an …
diverietti's user avatar
  • 7,902
2 votes

What is the holomorphic sectional curvature?

Maybe you already were aware of that, or maybe it really doesn't answer to your question, but I'll try anyhow... Take a look at this, Subsection 7.5 on page 39. The construction you talk about in you …
diverietti's user avatar
  • 7,902
2 votes
Accepted

Complex manifolds with trivial canonical bundle

I think the answers you are looking for are in this paper by V. Tosatti, see in particular Proposition 1.1, point (4) and Proposition 1.3. Warning (in view of the comment below by S.S.): the holonom …
diverietti's user avatar
  • 7,902
3 votes
Accepted

holomorphic sectional curvature and total scalar curvature

The answer to your question is exactly the same of the answer to this older question of mine. Enjoy!
Community's user avatar
  • 1
2 votes
Accepted

Decomposition of hermitian form used in the definition of Griffiths/Nakano positivity

With your notations, the hermitian form $\theta_E$ on $T_X\otimes E$ defined by $\Theta_E$ is given in a somewhat more extrinsic way by $$ \theta_E(v\otimes\sigma,v\otimes\sigma):=h(\Theta_E(v,\bar v) …
Community's user avatar
  • 1
2 votes
Accepted

Local expression involved in the definition of positivity of vector bundles

My answer will consist mainly of a collection of trivial facts but which nonetheless often generate some confusion. I begin by fixing some notation. Let $V$ be a complex vector space of complex dimen …
Community's user avatar
  • 1
15 votes

Non-Kahler Complex manifolds

Let $X$ be a compact complex manifold of complex dimension $n$. The Hodge-Frölicher spectral sequence starts with $$ E_1^{p,q}=H^{p,q}(X,\mathbb C) $$ and the limit term $E^{p,q}_\infty$ is the grade …
diverietti's user avatar
  • 7,902

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