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The aim of this paper is to introduce the $H^\infty$-functional calculus for harmonic functions over the quaternions. More precisely, we give meaning to Df(T) for unbounded sectorial operators T and polynomially growing functions of the…

Functional Analysis · Mathematics 2023-10-20 Antonino de Martino , Stefano Pinton , Peter Schlosser

The Fueter mapping theorem gives a constructive way to extend holomorphic functions of one complex variable to monogenic functions, i.e., null solutions of the generalized Cauchy-Riemann operator in $\mathbb{R}^4$, denoted by $\mathcal{D}$.…

Spectral Theory · Mathematics 2022-11-18 Antonino De Martino , Stefano Pinton

The $S$-functional calculus for slice hyperholomorphic functions generalizes the Riesz-Dunford-functional calculus for holomorphic functions to quaternionic linear operators and to $n$-tuples of noncommuting operators. For an unbounded…

Spectral Theory · Mathematics 2016-02-15 Jonathan Gantner

Holomorphic functions are fundamental in operator theory and their Cauchy formula is a crucial tool for defining functions of operators. The Fueter-Sce extension theorem (often called Fueter-Sce mapping theorem) provides a two-step…

Spectral Theory · Mathematics 2024-10-11 Fabrizio Colombo , Antonino De Martino , Stefano Pinton , Irene Sabadini , Peter Schlosser

The spectral theory on the $S$-spectrum originated to give quaternionic quantum mechanics a precise mathematical foundation and as a spectral theory for linear operators in vector analysis. This theory has proven to be significantly more…

Functional Analysis · Mathematics 2025-01-27 Fabrizio Colombo , Antonino De Martino , Stefano Pinton

Holomorphic functions play a crucial role in operator theory and the Cauchy formula is a very important tool to define functions of operators. The Fueter-Sce-Qian extension theorem is a two steps procedure to extend holomorphic functions to…

Spectral Theory · Mathematics 2023-03-02 Fabrizio Colombo , Antonino De Martino , Stefano Pinton , Irene Sabadini

The Fueter theorem provides a two step procedure to build an axially monogenic function, i.e. a null-solutions of the Cauchy-Riemann operator in $ \mathbb{R}^4$, denoted by $ \mathcal{D}$. In the first step a holomorphic function is…

Functional Analysis · Mathematics 2022-07-20 Antonino De Martino , Stefano Pinton

The fine structures on the $S$-spectrum constitute a new research area that includes a class of functional calculi based on the $S$-spectrum and on integral transforms determined by the Fueter--Sce mapping theorem and the Cauchy formula for…

Functional Analysis · Mathematics 2026-03-17 Fabrizio Colombo , Antonino De Martino , Joao Marques Da Costa

In this paper, we utilize various integral representations derived from the Fueter-Sce extension theorem, to introduce novel functional calculi tailored for quaternionic operators of sectorial type. Specifically, due to the different…

Functional Analysis · Mathematics 2024-02-23 Fabrizio Colombo , Stefano Pinton , Peter Schlosser

In this paper we extend the $H^\infty$ functional calculus to quaternionic operators and to $n$-tuples of noncommuting operators using the theory of slice hyperholomorphic functions and the associated functional calculus, called…

Functional Analysis · Mathematics 2015-11-25 D. Alpay , F. Colombo , T. Qian , I. Sabadini

Since 2006 the theory of slice hyperholomorphic functions and the related spectral theory on the S-spectrum have had a very fast development. This new spectral theory based on the S-spectrum has applications, for example, in the formulation…

Functional Analysis · Mathematics 2021-11-15 Daniel Alpay , Fabrizio Colombo , Kamal Diki , Irene Sabadini

The aim of this paper is to give an overview of the spectral theories associated with the notions of holomorphicity in dimension greater than one. A first natural extension is the theory of several complex variables whose Cauchy formula is…

Spectral Theory · Mathematics 2020-11-24 Fabrizio Colombo , Jonathan Gantner , Stefano Pinton

In this paper, we prove that slice polyanalytic functions on quaternions can be considered as solutions of a power of some special global operator with nonconstant coefficients as it happens in the case of slice hyperholomorphic functions.…

Complex Variables · Mathematics 2021-01-06 Daniel Alpay , Kamal Diki , Irene Sabadini

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…

Complex Variables · Mathematics 2025-05-13 Fabrizio Colombo , Antonino De Martino , Irene Sabadini

In 2016, the spectral theory on the $S$-spectrum was used to establish the $H^\infty$-functional calculus for quaternionic or Clifford operators. This calculus applies for example to sectorial or bisectorial right linear operators $T$ and…

Spectral Theory · Mathematics 2025-05-06 Fabrizio Colombo , Francesco Mantovani , Peter Schlosser

In this paper we study the additive splitting associated to the quaternionic Cauchy transform defined by the Cauchy formula of slice hyperholomorphic functions. Moreover, we introduce and study the analogue of the fundamental solution of…

Complex Variables · Mathematics 2019-01-30 Fabrizio Colombo , Samuele Mongodi

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…

Functional Analysis · Mathematics 2026-02-05 F. Colombo , A. De Martino , S. Pinton

The aim of this work is to define a continuous functional calculus in quaternionic Hilbert spaces, starting from basic issues regarding the notion of spherical spectrum of a normal operator. As properties of the spherical spectrum suggest,…

Functional Analysis · Mathematics 2013-06-17 Riccardo Ghiloni , Valter Moretti , Alessandro Perotti

We define a smooth functional calculus for a non-commuting tuple of (unbounded) operators $A_j$ on a Banach space with real spectra and resolvents with temperate growth, by means of an iterated Cauchy formula. The construction is also…

Spectral Theory · Mathematics 2007-05-23 Mats Andersson , Johannes Sjoestrand

The main purpose of this work is the construction of an analytic functional calculus for Clifford operators, which are operators acting on certain modules over Clifford algebras. Unlike in some preceding works by other authors, we use a…

Functional Analysis · Mathematics 2020-08-18 Florian-Horia Vasilescu
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