Bifurcation Loci of Exponential Maps and Quadratic Polynomials: Local Connectivity, Triviality of Fibers, and Density of Hyperbolicity

TL;DR

This paper investigates the structure of bifurcation loci in quadratic and exponential maps, proving connectedness for exponential maps and discussing conjectures related to local connectivity, fibers, and hyperbolic dynamics density.

Contribution

It proves the connectedness of the exponential bifurcation locus and explores conjectures on local connectivity and fibers for quadratic and exponential maps.

Findings

Exponential bifurcation locus is connected.

Local connectivity of the Mandelbrot set implies density of hyperbolic maps.

Triviality of fibers generalizes local connectivity for exponential maps.

Abstract

We study the bifurcation loci of quadratic (and unicritical) polynomials and exponential maps. We outline a proof that the exponential bifurcation locus is connected; this is an analog to Douady and Hubbard's celebrated theorem that (the boundary of) the Mandelbrot set is connected. For these parameter spaces, a fundamental conjecture is that hyperbolic dynamics is dense. For quadratic polynomials, this would follow from the famous stronger conjecture that the bifurcation locus (or equivalently the Mandelbrot set) is locally connected. It turns out that a formally slightly weaker statement is sufficient, namely that every point in the bifurcation locus is the landing point of a parameter ray. For exponential maps, the bifurcation locus is not locally connected. We describe a different conjecture (triviality of fibers) which naturally generalizes the role that local connectivity has for quadratic or unicritical polynomials.