The topology of the set of non-escaping endpoints

TL;DR

This paper investigates the topological structure of endpoints in Julia sets of transcendental entire functions, revealing a dichotomy in their properties and extending known results to broader function classes.

Contribution

It generalizes the endpoint dichotomy to large families in the Eremenko-Lyubich class and beyond, including the Fatou function, and explores their implications for spider's web structures.

Findings

Dichotomy between escaping and non-escaping endpoints holds for many functions.

Results extend to functions outside the Eremenko-Lyubich class, including the Fatou function.

Applications include demonstrating certain sets form spider's webs.

Abstract

There are several classes of transcendental entire functions for which the Julia set consists of an uncountable union of disjoint curves each of which joins a finite endpoint to infinity. Many authors have studied the topological properties of this set of finite endpoints. It was recently shown that, for certain functions in the exponential family, there is a strong dichotomy between the topological properties of the set of endpoints which escape and those of the set of endpoints which do not escape. In this paper, we show that this result holds for large families of functions in the Eremenko-Lyubich class. We also show that this dichotomy holds for a family of functions, outside that class, which includes the much-studied Fatou function defined by $f(z) := z + 1+ e^{-z}.$ Finally, we show how our results can be used to demonstrate that various sets are spiders' webs, generalising results such as those in a recent paper of the first author.