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Complex, contact, Riemannian, pseudo-Riemannian and Finsler geometry, relativity, gauge theory, global analysis.
27
votes
"The complex version of Nash's theorem is not true"
As Faisal says, there is no hope to have a general Nash-type theorem for all complex manifold, when the ambient space considered for the (isometric) embedding is some $\mathbb C^N$: no compact complex …
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 …
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 …
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 …
12
votes
Accepted
Relation between the de Rham and Hodge Laplacians on the Exterior Algebra
If $(X,\omega)$ is Kähler, then it is always true that
$$
\Delta'=\Delta''=\frac 12\Delta,
$$
where these three Laplacians are with respect, in order, to $\partial$, $\bar\partial$ and $d$. This is va …
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?
9
votes
Accepted
Negative holomorphic sectional curvature
Here is the answer.
Let $(X,\omega)$ be a Kähler $n$-dimensional manifold. Fix a point $x_0\in X$ an choose local holomorphic coordinates $(z_1,\dots,z_n)$ centered at $x_0$ and such that $(\partial/ …
9
votes
Accepted
Differential forms on an almost complex manifold
Call $C^{\infty}_{p,q}(M)$ the space of smooth complex sections of the bundle $\Lambda^{p,q}T^*_M$ and let $2n$ be the real dimension of $M$.
The fact that
$$
dC^{\infty}_{p,q}(M)\subset C^{\infty}_ …
9
votes
On the generalized Gauss-Bonnet theorem
Maybe what follows is not exactly what you are looking for, but it gives you an answer at least when you don't want to restrict yourself to the tangent bundle and work rather with general (complex) ve …
8
votes
Positive (k.k)-form?
I will try to clarify a little bit your question and at the same time to give you an answer.
All that I say, you can find on Demailly's book "Complex Analytic and Differential Geometry".
GENERAL THEO …
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 …
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 …
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 …
5
votes
Accepted
Holonomy of a Kähler manifold
The answer is yes.
The holonomy principle states that a given a riemannian manifold $(M,g)$ and a point $x\in M$, the datum of a parallel tensor field of a given type is equivalent to the datum of a …
5
votes
A question on Ricci curvature and Ricci form.
The whole point is that if the metric is Kähler, then the Chern connection coincides with the complexification of Levi-Civita connection of the riemanian metric on the underlying real manifold given b …