Universality property of the $S$-functional calculus, noncommuting matrix variables and Clifford operators

TL;DR

This paper demonstrates that the $S$-functional calculus and spectral theory are highly general, encompassing complex, quaternionic, and Clifford cases, and possess a universality property that extends their applicability to noncommuting matrix and operator variables.

Contribution

It establishes the universality of the $S$-functional calculus, showing its broad applicability across different algebraic settings and extending spectral theory to noncommuting operators.

Findings

$S$-spectrum is well defined in complex-structured algebras and Banach modules.

The $S$-functional calculus has a universality property.

Applicable to noncommuting matrix and operator variables.

Abstract

The spectral theory on the $S$-spectrum was born out of the need to give quaternionic quantum mechanics (formulated by Birkhoff and von Neumann) a precise mathematical foundation. Then it turned out that this theory has important applications in several fields such as fractional diffusion problems and, moreover, it allows one to define several functional calculi for $n$-tuples of noncommuting operators. With this paper we show that the spectral theory on the $S$-spectrum is much more general and it contains, just as particular cases, the complex, the quaternionic and the Clifford settings. More precisely, we show that the $S$-spectrum is well defined for objects in an algebra that has a complex structure and for operators in general Banach modules. We show that the abstract formulation of the $S$-functional calculus goes beyond quaternionic and Clifford analysis. Indeed we show that the $S$-functional calculus has a certain {\em universality property}. This fact makes the spectral theory on the $S$-spectrum applicable to several fields of operator theory and allows one to define functions of noncommuting matrix variables, and operator variables, as a particular case.