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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.

11 votes
Accepted

Intersections in almost complex manifolds

Let me answer the easy part now and then come back later for the (slightly) more delicate singular case: If $(M,J)$ is a real-analytic almost-complex manifold and $X,Y\subset M$ are almost-complex su …
Robert Bryant's user avatar
4 votes
Accepted

Can we always solve this equation in the space of Hermitian structures on a complex vector b...

If $E$ has rank $0$ or $1$, 'yes', otherwise, 'no'. Just do a dimension count. You'll find that you have (many) more unknowns than equations and, for general $h$ and $h''$, there will be no solution …
Robert Bryant's user avatar
4 votes

Closed parallel (1,1)-forms on compact Kähler manifolds

Take a compact complex torus with a Kähler structure, say, an abelian variety, for example. Then there are lots of non-vanishing closed parallel $(1,1)$-forms, and their products will generate $(p,p) …
Robert Bryant's user avatar
3 votes

Is every positive $(n-1,n-1)$ form almost decomposable?

Not sure why you aren't asking for a $\chi$ such that $\alpha = \chi^{n-1}$, as this surely exists and doesn't require compactness. The point is that $\alpha$ is positive by construction and, for any …
Robert Bryant's user avatar
5 votes
Accepted

Pull-backs of $\sum dx_i \wedge dy_i$ under radial diffeomorphisms of $\mathbb C^n$

Yes, it's true, and it follows immediately from a simple calculation: Since $f$ is assumed to be a function of $|z|$ such that $\phi(z) = f(|z|)z$ is a smooth diffeomorphism, it follows that $\mathrm …
Robert Bryant's user avatar
3 votes

Analogue of Infinitesimal Schwarzian for holomorphic $(G,X)$-manifolds

To add to what Ben said: Typically the resolution of the sheaf mapping ${\frak{g}}\to\Gamma(TX)$ is the Spencer resolution, which is a canonical $G$-equivariant exact sequence of differential operato …
Robert Bryant's user avatar
2 votes
Accepted

pull back of a Kähler form by a smooth circle group action on a compact Kähler manifold

Now that I fully understand your question, which (apparently) is whether every circle action on a compact Kähler manifold $(M,J,\omega)$ must preserve the $J$-type of $\omega$, I can answer it. The a …
Robert Bryant's user avatar
6 votes
Accepted

Does $\partial\overline{\partial}f=0$ imply $f\equiv c$ for particular kind of $f$?

Yes, this is true. The point is that $\partial\bar\partial f = 0$ on the complement $C$ of a ball in $\mathbb{C}^n$ ($n\ge 2$) implies that $f = h_+ + \overline{h_-}$ for some functions $h_\pm$ that …
Robert Bryant's user avatar
11 votes
Accepted

How to deduce this equation for a 4-dim almost Kahler manifold?

Here is one way to do this computation: Choose a local coframing $\eta = (\eta_i)$ in which $g = {\eta_1}^2{+}{\eta_2}^2{+}{\eta_3}^2{+}{\eta_4}^2$ and $\omega = \eta_1\wedge\eta_2{+}\eta_3\wedge\et …
Robert Bryant's user avatar
4 votes
Accepted

almost complex $\mathbb{Z}^{6}$-action

Here is a construction of a family of such examples that will work, but you will have to choose a particular map to get an explicit example. Let's use coordinates $v_1,v_2,v_3,v_4,x,y$ (each periodic …
Robert Bryant's user avatar
4 votes
Accepted

about Kahler curvature tensor on page 77 of Besse's book "Einstein Manifolds"

Well, $B$, as defined in Besse on page 77, is not the Bochner curvature because it is not traceless when $m>1$ (cf. (2.64)). I believe that $B_0$ is some version of the Bochner curvature tensor. I …
Robert Bryant's user avatar
9 votes
Accepted

First Chern class vanishes on a Lagrangian submanifold

Yes, if you ignore 2-torsion: After all, if you give $TM$ a complex structure compatible with $\omega$, say $J$, then you'll have that $TM$ pulls back to $L$ to become isomorphic to $TL\oplus T^*L\si …
Robert Bryant's user avatar
6 votes
Accepted

What is the definition of a Calabi-Yau metric on a non-compact manifold?

There are two slightly different definitions. The first is that it is a Kähler metric that is Ricci-flat, and the second is that it is a Kähler metric on a (usually connected) complex $n$-manifold wi …
Robert Bryant's user avatar
5 votes
Accepted

Can the $(n-1)$ power of the hermitian form on a compact complex $n$-fold be $\partial {\bar...

Yes, this can happen. For a simple example, consider $M = \mathrm{SL}(2,\mathbb{C})/\Lambda$ where $\Lambda\subset \mathrm{SL}(2,\mathbb{C})$ is a discrete, co-compact lattice. Then $M$ is a compact …
Robert Bryant's user avatar
12 votes
Accepted

Determine whether a (1,2) tensor is Nijenhuis tensor

Yes, there are pointwise algebraic conditions on a section $N$ of $T\otimes\Lambda^2(T^*)$ in order for $N$ to equal $N_J$ for some almost complex structure $J$, but there are differential conditions …
Robert Bryant's user avatar

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