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Harmonic and polyanalytic functional calculi have been recently defined for bounded commuting operators. Their definitions are based on the Cauchy formula of slice hyperholomorphic functions and on the factorization of the Laplace operator…

Spectral Theory · Mathematics 2023-04-21 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 $S$-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

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-Sce-Qian mapping theorem is a two steps procedure to extend holomorphic functions of one complex variable to quaternionic or Clifford algebra-valued functions in the kernel of a suitable generalized Cauchy-Riemann operator. Using…

Complex Variables · Mathematics 2021-12-10 Fabrizio Colombo , Antonino De Martino , Irene Sabadini

In this paper we introduce the two possible formulations of the F-functional calculus which are based on the Fueter-Sce mapping theorem in integral form and we introduce the pseudo F-resolvent equation. In the case of dimension 3 we prove…

Functional Analysis · Mathematics 2014-03-18 Fabrizio Colombo , 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

we start the study of Schur analysis in the quaternionic setting using the theory of slice hyperholomorphic functions. The novelty of our approach is that slice hyperholomorphic functions allows to write realizations in terms of a suitable…

Functional Analysis · Mathematics 2011-10-13 Daniel Alpay , Fabrizio Colombo , Irene Sabadini

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 spectral theory on the S-spectrum was introduced to give an appropriate mathematical setting to quaternionic quantum mechanics, but it was soon realized that there were different applications of this theory, for example, to fractional…

Spectral Theory · Mathematics 2022-05-18 Fabrizio Colombo , Antonino De Martino , Stefano Pinton , Irene Sabadini

Integral relations with the Cauchy kernel on a semi-axis for the Laguerre polynomials, the confluent hypergeometric function, and the cylindrical functions are derived. A part of these formulas is obtained by exploiting some properties of…

Complex Variables · Mathematics 2018-10-01 Y. A. Antipov , S. M. Mkhitaryan

We introduce the notion of rationality for hyperholomorphic functions (functions in the kernel of the Cauchy-Fueter operator). Following the case of one complex variable, we give three equivalent definitions: the first in terms of…

Functional Analysis · Mathematics 2007-05-23 D. Alpay , M. Shapiro , D. Volok

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

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

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

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

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

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

In this paper, we first prove that the S-spectrum of a bounded right quaternionic linear operator on a two-sided quaternionic Banach space is a union of the spectrum of some bounded linear operators on a complex Banach space. Furthermore,…

Functional Analysis · Mathematics 2020-05-21 El Hassan Benabdi , Mohamed Barraa

The S-functional calculus is a functional calculus for $(n+1)$-tuples of non necessarily commuting operators that can be considered a higher dimensional version of the classical Riesz-Dunford functional calculus for a single operator. In…

Functional Analysis · Mathematics 2013-10-30 Daniel Alpay , Fabrizio Colombo , Jonathan Gantner , Irene Sabadini
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