Singularities of slice regular functions over real alternative *-algebras

TL;DR

This paper classifies singularities of slice regular functions over real alternative *-algebras, extending complex and quaternionic theories with new series expansions and topological insights into zero sets.

Contribution

It introduces a new series expansion near singularities and provides a complete classification, advancing the understanding of slice regular functions over broader algebraic structures.

Findings

Complete classification of singularities

Introduction of a new series expansion method

Analysis of zero set topology and semiregular functions

Abstract

The main goal of this work is classifying the singularities of slice regular functions over a real alternative *-algebra A. This function theory has been introduced in 2011 as a higher-dimensional generalization of the classical theory of holomorphic complex functions, of the theory of slice regular quaternionic functions launched by Gentili and Struppa in 2006 and of the theory of slice monogenic functions constructed by Colombo, Sabadini and Struppa since 2009. Along with this generalization step, the larger class of slice functions over A has been defined. We introduce here a new type of series expansion near each singularity of a slice regular function. This instrument, which is new even in the quaternionic case, leads to a complete classification of singularities. This classification also relies on some recent developments of the theory, concerning the algebraic structure and the zero sets of slice functions. Peculiar phenomena arise, which were not present in the complex or quaternionic case, and they are studied by means of new results on the topology of the zero sets of slice functions. The analogs of meromorphic functions, called (slice) semiregular functions, are introduced and studied.