New Taylor and Laurent series of axially harmonic, Fueter regular and polyanalytic functions (2505.06555v1)

Abstract: The Fueter-Sce mapping theorem stands as one of the most profound outcomes in complex and hypercomplex analysis, producing hypercomplex generalizations of holomorphic functions. In recent years, delving into the factorization of the second operator appearing in the Fueter-Sce mapping theorem has uncovered its potential to generate novel classes of functions and their respective functional calculi. The sets of functions obtained from this factorization and the associated functional calculi define the so-called {\em fine structures on the $S$-spectrum}. This paper aims to comprehensively investigate the function theories for the fine structures of Dirac type in the quaternionic framework, presenting new series expansions for axially harmonic, Fueter regular, and axially polyanalytic functions. These series expansions are highly nontrivial. In fact, when considering the hypercomplex realm, specifically the quaternionic or the Clifford setting, extending the concept of complex power series expansion is not immediate, and different Taylor and Laurent expansions appear with different sets of convergence. Additionally, our objectives include establishing the representation formulas for these function spaces; such formulas encode the fundamental properties of the functions and have numerous consequences. Finally, in the last section of this paper, we explain the applications of the fine structures in operator theory.