On the automorphic group of an entire function

TL;DR

This paper advances the theory of the automorphic group of entire functions, exploring its geometric and analytic properties and aiming to develop tools similar to those used in hyperbolic geometry and number theory.

Contribution

It extends Shimizu's foundational work by investigating the global properties of automorphic groups of entire functions, setting the stage for future generalizations of arithmetic and analytic methods.

Findings

Analyzed geometric structures induced by automorphic groups

Identified similarities with hyperbolic and arithmetic groups

Proposed directions for applying trace formulas to entire functions

Abstract

This paper develops further the theory of the automorphic group of non-constant entire functions. This theory has already a long history that essentially started with two remarkable papers of Tatsujir\^o Shimizu that were published in 1931. The elements $\phi(z)$ of the group are defined by the automorphic equation $f(\phi(z))=f(z)$, were $f(z)$ is entire. Tatsujir\^o Shimizu also refers to the functions of this group as those functions that are determined by $f^{-1}\circ f$. He proved many remarkable properties of those automorphic functions. He indicated how they induce a beautiful geometric structure on the complex plane. Those structures were termed by Tatsujir\^o Shimizu, the system of normal polygonal domains, and the more refined system of the fundamental domains of $f(z)$. The last system if exists tiles up the complex plane with remarkable geometric tiles that are conformally mapped to one another by the automorphic functions. In the Ph.D thesis of the author, those tiles were also called the system of the maximal domains of $f(z)$. One can not avoid noticing the many similarities between this automorphic group and its accompanying geometric structures and analytic properties, and the more tame discrete groups that appear in the theory of hyperbolic geometry and also the arithmetic groups in number theory. This paper pursues further the theory initiated by Tatsujir\^o Shimizu, towards understanding global properties of the automorphic group, rather than just understanding the properties of the individual automorphic functions. We hope to be able in sequel papers to generalize arithmetic and analytic tools such as the Selberg trace formula, to this new setting.