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Complex analysis, holomorphic functions, automorphic group actions and forms, pseudoconvexity, complex geometry, analytic spaces, analytic sheaves.

27 votes

Are the algebraic numbers dense everywhere on the boundary of the Mandelbrot set?

Post-critically pre-periodic quadratic polynomials, i.e. those for which the orbit of the critical point $0$ is pre-periodic, are well-known to be dense in the boundary of the Mandelbrot set. (This is …
Lasse Rempe's user avatar
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7 votes

Entire function which diverges along every path

To add a little bit more background in addition to Robert's answer: The first thing to clarify is what you mean by "diverges". Like Robert, I think you mean "does not converge to a finite value". How …
Lasse Rempe's user avatar
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6 votes
Accepted

How bad can a circle domain get?

Let $K$ be the boundary of your circle domain $\Omega$. Let us suppose that every point of $K$ is accumulated on by a sequence of (pairwise different) circle components. Such an example is easy to c …
Lasse Rempe's user avatar
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6 votes

Functions holomorphic on a region minus a Cantor set

Removability with respect to homeomorphisms is different from the removability with respect to bounded functions mentioned in another answer. In particular, it is not necessary to have Hausdorff dime …
Lasse Rempe's user avatar
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6 votes

Holomorphic function bounded in a sector with angle $>\pi$

Let $L$ be the boundary of the strip $$ G := \{a + ib\colon a>0, -\pi < b < \pi\}, $$ parameterised in clockwise direction. Define $$ F_0\colon \mathbb{C}\setminus \overline{G}\to\mathbb{C}; \quad z\m …
Lasse Rempe's user avatar
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6 votes

Is an entire function, with nowhere vanishing derivative, always a covering map?

To put the questions and answers in a wider context, the set of singular values $S(f)$ of an entire function $f$ is the set of points $w$ near which $f$ is not a covering map. That is, $w$ is regular …
Lasse Rempe's user avatar
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6 votes
Accepted

Is there any elementary proof of No wandering domain for polynomials

If by "elementary method", you mean a proof that avoids using techniques from quasiconformal methods, then the short answer is "no". Giving a different proof of the No Wandering Domains (NWD) theorem, …
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6 votes

Interesting results for open Riemann surfaces

I hope that the following result by Bishop and myself might be "interesting": Every open Riemann surface is a cover over the sphere, branched over only three points. Equivalently, every open Riemann s …
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5 votes
Accepted

A question on $J(f)$ and $J(f')$

In my opinion, the question is completely arbitrary. There is no reason to expect relationships between the dynamics of $f$ and that of its derivative. Their relationship will even change under affine …
Lasse Rempe's user avatar
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5 votes

A question on Ahlfors covering surface

If you read French, the article "Sur la théorie d'Ahlfors des surfaces" by Duval may be interesting: http://arxiv.org/abs/1311.1589 . It covers the full Ahlfors theory, not just the islands theorem. …
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5 votes

Complex function for mapping a circle to a superellipse

As Adam stated, the Riemann mapping theorem provides the function that you are looking for. However, the Riemann mapping will not be given by an explicit formula, except in particularly simple cases. …
Lasse Rempe's user avatar
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5 votes
Accepted

Conformal map and Jordan curve

If $G\neq\mathbb{C}$ is a s.c. domain, then a conformal map to a disc extends analytically beyond the boundary if and only if $G$ is bounded by an analytic Jordan curve. In particular, if you were to …
Lasse Rempe's user avatar
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5 votes
Accepted

A generalization of Liouvilles Theorem for entire functions

To elaborate on my comment, choose three pairwise disjoint Jofrdan $U_1$, $U_2$, $U_3$ whose boundary passes through infinity, and let $\gamma_i\subset U_i$ be a curve to infinity for each $i$. Fix $\ …
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5 votes
Accepted

On the existence of a holomorphic logarithm

I believe that your suggestion is correct: $\newcommand{\C}{\mathbb{C}}$ THEOREM. Suppose that $U,V\subset\mathbb{C}$ are domains, and that $f:U\to V$ is a conformal isomorphism. Then $f'$ has a ( …
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5 votes
Accepted

Domain of Holomorphy

Further to Ben's answer, it might be useful to picture the situation in $\mathbb{C}$. (Of course in $\mathbb{C}$ every domain is a domain of holomorphy, but we can still exhibit the same phenomenon th …
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