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Complex analysis, holomorphic functions, automorphic group actions and forms, pseudoconvexity, complex geometry, analytic spaces, analytic sheaves.
6
votes
Accepted
Nontrivial extension of the action of complex hyperbolic group $H$ on $\mathbb{C}$
The group $H$ acts transitively and primitively on $\mathbb{C}=\mathbb{R}^2$. ('Primitive' means that $H$ preserves no nontrivial foliation.) It's a consequence of the classification of transitive pr …
1
vote
Characterization of bi-Hermitian structures with equal Lee forms
There are probably too many such $(M,g,I_+,I_-)$ to really expect a 'classification'.
For instance, consider the case when a complex manifold $(M,I_+)$ has real dimension $4$, and the $I_+$-holomorphi …
4
votes
Accepted
Existence of complex function?
The answer is 'yes' there do exist such functions that are non-constant with singularities only along surfaces $\Sigma\subset\mathbb{C}^2$, and here is how one can understand them:
First, it helps to …
4
votes
Accepted
Complex-doubly periodic function in two variables?
The answer is that the only solutions have the form
$$
f = (f_1,f_2) = \bigl(c, h(\,\overline{z}_1, z_2)\bigr)
$$
where $h:\mathbb{C}^2\to\mathbb{C}$ is holomorphic and $c$ is a constant,
which must e …
2
votes
Accepted
Beltrami equation with harmonic coefficient
Note that, if you take $\phi=0$, then the equation reduces to $w_y =0$, i.e., if $D\subset C$ is the domain of $w$ and $x:D\to\mathbb{R}$ is the projection on the $x$-axis and has connected fibers, t …
3
votes
Complex manifold defined over $\mathbb{R}$
There is a trivial construction that shows that the answer is 'yes' for all complex manifolds, not just those that admit an anti-holomorphic involution.
Let $(M,J)$ be a (finite-dimensional) complex $ …
7
votes
Conformal map from a 7-sided polyhedron to a square pyramid
No such conformal map exists.
Conformal mapping in dimensions above 2 is very different from conformal mapping in dimension 2. In dimensions above 2, any conformal mapping is a (finite) composition …
7
votes
Accepted
An estimate on deviation of two smooth tangent $J$-holomorphic curves
Yes, this is true. In fact, a more precise statement holds: Unless $f$ vanishes identically on $\mathbb{D}$, there is an integer $n$ and a nonzero complex number $a$ such that $f(z) = a\,z^n + f_{n+ …
3
votes
Regularity for the roots of (characteristic) polynomials with given multiplicity
I think that there is a smooth (or analytic) result of the kind that you are seeking:
Let $M^m$ be a connected smooth (or analytic) manifold, and let $P:M\times\mathbb{R}\to\mathbb{R}$ be a smooth …
4
votes
Accepted
Criterion for homogeneity
Edit: (21 May 2017) I have modified my answer to cover the case that the OP meant to ask, i.e., the assumption is that the closure of an orbit has nonempty interior.
Now that you have added the assu …
2
votes
Accepted
Nonlinear PDE for a 2D foliation
It's easy to derive a third-order (nonlinear) differential equation for $u(x,y)$ that satisfies your conditions (1) and (2): Namely, set $\theta(x,y) = \arctan\bigl(u_y(x,y)/u_x(x,y)\bigr)$ and then …
3
votes
harmonic extension of a curve by different parametrization
The answer to (1) in the space case is a definite 'no'. The actual image 'surface' $h(\Delta)$ in $\mathbb{R}^3$ can actually change when you reparametrize with $\phi:S^1\to S^1$, in which case, ther …
1
vote
Accepted
Lifting quadratic forms on the cotangent bundle to higher level forms
I think that the answer to your question(s), when everything is sorted out, is 'no'. What is actually going on in the complex case that you are concerned with is that there are two Hermitian forms in …
2
votes
Accepted
closed integral formula for a non-zero solution of a homogeneous linear ODE of order 2
The answer is basically 'no', there is no 'elementary method' involving elementary operations and quadrature (i.e., finding antiderivatives of known holomorphic functions) that will give you a solutio …
4
votes
Accepted
Special Kähler normal coordinates around a point
I don't know a reference, but this desired normal form is, indeed, attainable. Here is the argument:
Assume given a Kähler form $\omega$ defined on a neighborhood of $0\in\mathbb{C}^n$ and that ther …