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The objective of this article is to study nearly invariant subspaces of the backward shift operator on the real Hardy space. We also investigate nearly invariant subspaces with finite defect, and as a consequence, provide a characterization…

Functional Analysis · Mathematics 2026-04-14 Arshad Khan , Sneh Lata , Dinesh Singh

Let $H(\mathbb{D})$ be the space of all analytic functions in the unit disc $\mathbb{D}$. For $g\in H(\mathbb{D})$, the generalized Hilbert operator $\mathcal{H}_{g}$ is defined by $$\mathcal{H}_{g}(f)(z)=\int_{0}^{1}f(t)g'(tz)dt, \ \ z\in…

Functional Analysis · Mathematics 2026-01-14 Pengcheng Tang

We aim to give a self-contained and detailed yet simplified account of the foundations of the theory of double operator integrals, in order to provide an accessible entry point to the theory. We make two new contributions to these…

Mathematical Physics · Physics 2025-10-31 Robert Ferydouni , Daniel D. Spiegel

We show that if a nonscalar operator on a separable Hilbert space has a nontrivial invariant subspace, then it has also a nontrivial hyperinvariant subspace. Thus the hyperinvariant subspace problem is equivalent to the invariant subspace…

Functional Analysis · Mathematics 2025-04-01 László Kérchy , Carl Pearcy

Let $\mathcal{M}$ be a von Neumann algebra equipped with a normal semifinite faithful trace, $(\mathbb{X},\,d,\,\mu)$ be a space of homogeneous type in the sense of Coifman and Weiss, and…

Functional Analysis · Mathematics 2023-11-28 Zhijie Fan , Guixiang Hong , Wenhua Wang

The notion of slant H-Toeplitz operator $V_\phi$ on the Hardy space $H^2$ is introduced and its characterizations are obtained. We have shown that an operator on the space $H^2$ is slant H-Toeplitz if and only if its matrix is a slant…

Functional Analysis · Mathematics 2018-01-15 Anuradha Gupta , Shivam Kumar Singh

This is an expository article about operads in homotopy theory written as a chapter for an upcoming book. It concentrates on what the author views as the basic topics in the homotopy theory of operadic algebras: the definition of operads,…

Algebraic Topology · Mathematics 2022-01-04 Michael A. Mandell

We study the intertwining relations between analytic Toeplitz operators induced on the Hardy space H^2 by analytic functions bounded on the open unit disc. Our work centers on the connection between intertwining between the Toeplitz…

Functional Analysis · Mathematics 2009-03-31 Paul S. Bourdon , Joel H. Shapiro

This paper studies the behaviour of iterates of weighted composition operators acting on spaces of analytic functions, with particular emphasis on the Hardy space $H^2$. Questions relating to uniform, strong and weak convergence are…

Functional Analysis · Mathematics 2020-02-11 I. Chalendar , J. R. Partington

Truncated Toeplitz operators and their asymmetric versions are studied in the context of the Hardy space $H^p$ of the half-plane for $1<p<\infty$. It is shown that they are equivalent after extension to $2 \times 2$ matricial Toeplitz…

Functional Analysis · Mathematics 2015-04-27 M. Cristina Câmara , Jonathan R. Partington

We prove that the invariant subspaces of the Hardy operator on $L^2[0,1]$ are the spaces that are limits of sequences of finite dimensional spaces spanned by monomial functions.

Functional Analysis · Mathematics 2022-07-05 Jim Agler , John E. McCarthy

We first extend the multiplicativity property of arithmetic functions to the setting of operators on the Fock space. Secondly, we use phase operators to get representation of some extended arithmetic functions by operators on the Hardy…

Functional Analysis · Mathematics 2018-12-27 F. Bouzeffour , M. Garayev

We are concerned with Hardy and BMO spaces of operator-valued functions analytic in the unit disk of $\mathbb{C}.$ In the case of the Hardy space, we involve the atomic decomposition since the usual argument in the scalar setting is not…

Functional Analysis · Mathematics 2010-02-19 Zeqian Chen

We give an exposition on the $L^2$ theory of the perturbed Fourier transform associated with a Schr\"odinger operator $H=-d^2/dx^2 +V$ on the real line, where $V$ is a real-valued \mbox{finite} measure. In the case $V\in L^1\cap L^2$, we…

Analysis of PDEs · Mathematics 2025-03-20 Shijun Zheng

Hausdorff operators on the real line and multidimensional Euclidean spaces originated from some classical summation methods. Now it is an active research area. Hausdorff operators on general groups were defined and studied by the author…

Functional Analysis · Mathematics 2020-08-11 A. R. Mirotin

In this article, we show that multilinear fractional type operators are bounded from product Hardy spaces with variable exponents into Lebesgue spaces with variable exponents via the atomic decomposition theory. We also study continuity…

Classical Analysis and ODEs · Mathematics 2019-07-19 Jian Tan

We give an elementary proof of a formula recently obtained by Hammond, Moorhouse, and Robbins for the adjoint of a rationally induced composition operator on the Hardy space H^2. We discuss some variants and implications of this formula,…

Functional Analysis · Mathematics 2009-03-20 Paul S. Bourdon , Joel H. Shapiro

The symmetrized bidisc has been a rich field of holomorphic function theory and operator theory. A certain well-known reproducing kernel Hilbert space of holomorphic functions on the symmetrized bidisc resembles the Hardy space of the unit…

Functional Analysis · Mathematics 2020-03-23 Tirthankar Bhattacharyya , B. Krishna Das , Haripada Sau

We show that a Krein-Feller operator is naturally associated to a fixed measure $\mu$, assumed positive, $\sigma$-finite, and non-atomic. Dual pairs of operators are introduced, carried by the two Hilbert spaces, $L^{2}\left(\mu\right)$ and…

Functional Analysis · Mathematics 2022-05-17 Palle E. T. Jorgensen , James Tian

This article describes Hilbert spaces contractively contained in certain reproducing kernel Hilbert spaces of analytic functions on the open unit disc which are nearly invariant under division by an inner function. We extend Hitt's theorem…

Functional Analysis · Mathematics 2025-02-19 Arshad Khan , Sneh Lata , Dinesh Singh