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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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 $ …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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+ …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar
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 …
Robert Bryant's user avatar

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