Transcendental operators acting on slice regular functions

The aim of this paper is to carry out an analysis of five trascendental operators acting on the space of slice regular functions, namely *-exponential, *-sine and *-cosine and their hyperbolic analogues. The first three of them were introduced by Colombo, Sabadini and Struppa and some features of *-exponential were investigated in a previous paper by Altavilla and the author. We show how exp*(f), sin*(f), cos*(f), sinh*(f) and cosh*(f) can be written in terms of the real and the vector part of the function f and we examine the relation between cos* and cosh* when the domain Omega is product and when it is slice. In particular we prove that when Omega is slice, then cos*(f) = cosh*(f * I) holds if and only if f is C-I preserving, while in the case Omega is product there is a much larger family of slice regular functions for which the above relation holds.

Automated summary

This paper analyzes five transcendental operators acting on the space of slice regular functions and examines their relationships. The study finds that there is a certain relationship between cos* and cosh* in specific domains.