Dynamics of Generalized Nevanlinna Functions

TL;DR

This paper extends the duality between parameter space and dynamical behavior observed in rational maps to a broader class of transcendental functions called generalized Nevanlinna functions, showing that hyperbolic components are bounded in certain families.

Contribution

It generalizes the duality concept to generalized Nevanlinna functions and proves boundedness of hyperbolic components in specific transcendental function families.

Findings

Duality extends to generalized Nevanlinna functions with no infinity asymptotic value.

In natural parameter slices, hyperbolic-like components have boundary points reflecting asymptotic tract behavior.

All hyperbolic components of period greater than 1 in certain families are bounded.

Abstract

In the early 1980's, computers made it possible to observe that in complex dynamics, one often sees dynamical behavior reflected in parameter space and vice versa. This duality was first exploited by Douady, Hubbard and their students in early work on rational maps. See \cite{DH,BH} for example. Here, we continue to study these ideas in the realm of transcendental functions. In \cite{KK1}, it was shown that for the tangent family, $\lambda \tan z$, the way the hyperbolic components meet at a point where the asymptotic value eventually lands on infinity reflects the dynamic behavior of the functions at infinity. In the first part of this paper we show that this duality extends to a much more general class of transcendental meromorphic functions that we call {\em generalized Nevanlinna functions} with the additional property that infinity is not an asymptotic value. In particular, we show that in "dynamically natural" one dimensional slices of parameter space, there are "hyperbolic-like" components with a unique distinguished boundary point whose dynamics reflect the behavior inside an asymptotic tract at infinity. Our main result is that {\em every} parameter point in such a slice for which the asymptotic value eventually lands on a pole is such a distinguished boundary point. In the second part of the paper, we apply this result to the families $\lambda \tan^p z^q$, $p,q \in \mathbb Z^+$, to prove that all hyperbolic components of period greater than $1$ are bounded.