A unified approach to the Dirac fine structures on the $S$-spectrum and a connection with Jacobi polynomials
This paper contributes to the recently introduced theory of fine structures on the $S$-spectrum. We study, in a unified way, the functional calculi for axially Poly-Analytic-Harmonic functions on the $S$-spectrum. Axially Poly-Analytic-Harmonic functions of type $(\beta, m)$, for $\beta, m \in \mathbb{N}_0$ belong to the kernel of the Dirac-Laplace operators $D^\beta\Delta^m_{n+1}$ of type $(\beta, m)$ and contain as particular cases Poly-Analytic and Poly-Harmonic functions of axial type. By applying these operators to the Cauchy kernels $S^{-1}_L(s,x)$ of (left) slice hyperholomorphic functions, we obtain an integral representation for axially Poly-Analytic-Harmonic functions. We point out that the kernels $D^\beta\Delta^m_{n+1}S^{-1}_L(s,x)$ have a remarkable connection with Jacobi polynomials. By replacing the paravector operator $T$ with commuting components in the kernels $D^\beta\Delta^m_{n+1} S^{-1}_L(s,x)$, we obtain the associated resolvent operators. With these resolvent operators, denoted by $S^{-1}_{L, D^\beta\Delta^m}(s,T)$, we define the associated functional calculi based on the $S$-spectrum and study their properties.