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The goal of the present paper is to push Sz.-Nagy--Foias model theory for a completely nonunitary Hilbert-space contraction operator $T$, to the case of a commuting pair of contraction operators $(T_1, T_2)$ having product $T = T_1 T_2$…

Functional Analysis · Mathematics 2018-10-01 Joseph A. Ball , Haripada Sau

We initiate the study of weighted multi-Toeplitz operators associated with noncommutative regular domains in B(H)^n. These operators are acting on the full Fock space with n generators and have as symbols free pluriharmonic functions.…

Functional Analysis · Mathematics 2018-12-18 Gelu Popescu

This article, addressed to a general audience of functional analysts, is intended to be an illustration of a few basic principles from `noncommutative functional analysis', more specifically the new field of {\em operator spaces.} In our…

Functional Analysis · Mathematics 2007-05-23 David P. Blecher , Damon M. Hay

The theory of characteristic functions for row contractions is used to determine the group $Aut(B(H)^n_1)$ of all free holomorphic automorphisms of the unit ball of $B(H)^n$. We show that the noncommutative Poisson transform commutes with…

Operator Algebras · Mathematics 2008-10-03 Gelu Popescu

This paper concerns free analytic maps on noncommutative domains. These maps are free analogs of classical holomorphic functions in several complex variables, and are defined in terms of noncommuting variables amongst which there are no…

Functional Analysis · Mathematics 2013-04-16 J. William Helton , Igor Klep , Scott McCullough

In this paper, we study free holomorphic functions on regular polyballs and provide analogues of several classical results from complex analysis such as: Abel theorem, Hadamard formula, Cauchy inequality, Schwarz lemma, and maximum…

Operator Algebras · Mathematics 2015-03-02 Gelu Popescu

In this paper we initiate the study of composition operators on the noncommutative Hardy space $H^2_{\bf ball}$. Several classical results about composition operators (boundedness, norm estimates, spectral properties, compactness,…

Functional Analysis · Mathematics 2011-11-15 Gelu Popescu

Multivariable operator theory is used to provide Bohr inequalities for free holomorphic functions with operator coefficients on the regular polyball. In addition, we obtain analogues of Caratheodory, Fejer, and Egervary-Szazs inequalities…

Functional Analysis · Mathematics 2017-09-29 Gelu Popescu

In this paper we introduce a hyperbolic distance $\delta$ on the noncommutative open ball $[B(H)^n]_1$, where $B(H)$ is the algebra of all bounded linear operators on a Hilbert space $H$, which is a noncommutative extension of the…

Functional Analysis · Mathematics 2009-11-29 Gelu Popescu

We introduce a notion of completely bounded holomorphic functions defined on the open unit ball of an operator space. We endow the set of these functions with an operator space structure, and in the scalar-valued case we identify an…

Functional Analysis · Mathematics 2024-05-16 Javier Alejandro Chávez-Domínguez , Verónica Dimant

We define the notion of a free resolution of a d-tuple $(T_1, T_2, . . . T_d)$ of mutually commuting operators acting on a Hilbert space H, and that this invariant gives rise to a class of vector space complexes parametrized by points in…

Functional Analysis · Mathematics 2007-05-23 Devin C. V. Greene

We prove an implicit function theorem and an inverse function theorem for free noncommutative functions over operator spaces and on the set of nilpotent matrices. We apply these results to study dependence of the solution of the initial…

Operator Algebras · Mathematics 2015-06-30 Gulnara Abduvalieva , Dmitry S. Kaliuzhnyi-Verbovetskyi

We study operator algebraic and function theoretic aspects of algebras of bounded nc functions on subvarieties of the nc domain determined by all levels of the unit ball of an operator space (nc operator balls). Our main result is the…

Operator Algebras · Mathematics 2025-04-15 Jeet Sampat , Orr Shalit

The goal of this paper is to study the structure of noncommutative weighted shifts, their properties, and to understand their role as models (up to similarity) for $n$-tuples of operators on Hilbert spaces as well as their implications to…

Functional Analysis · Mathematics 2024-04-16 Gelu Popescu

In this article we introduce powerful tools and techniques from invariant theory to free analysis. This enables us to study free maps with involution. These maps are free noncommutative analogs of real analytic functions of several…

Rings and Algebras · Mathematics 2019-08-15 Igor Klep , Špela Špenko

We show "free theorems" in the style of Wadler for polymorphic functions in homotopy type theory as consequences of the abstraction theorem. As an application, it follows that every space defined as a higher inductive type has the same…

Logic in Computer Science · Computer Science 2017-04-20 Taichi Uemura

In this paper we initiate the study of real operator monotonicity for functions of tuples of operators, which are multivariate structured maps with a functional calculus called free functions that preserve the order between real parts (or…

Functional Analysis · Mathematics 2019-12-19 Marcell Gaál , Miklós Pálfia

We give an entire free holomorphic function $f$ which is unbounded on the row ball. That is, we give a holomorphic free noncommutative function which is continuous in the free topology developed by Agler and McCarthy but is unbounded on the…

Functional Analysis · Mathematics 2019-08-20 J. E. Pascoe

In this paper, we study free k-pluriharmonic functions on noncommutative regular polyballs. These regular polyballs have universal operator models consisting of left creation operators acting on tensor products of full Fock spaces. We…

Operator Algebras · Mathematics 2016-04-14 Gelu Popescu

We characterize functions of $d$-tuples of bounded operators on a Hilbert space that are uniformly approximable by free polynomials on balanced open sets.

Functional Analysis · Mathematics 2015-09-04 Jim Agler , John E. McCarthy