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One approach to multivariate operator theory involves concepts and techniques from algebraic and complex geometry and is formulated in terms of Hilbert modules. In these notes we provide an introduction to this approach including many…

Functional Analysis · Mathematics 2007-11-28 Ronald G. Douglas

False theta functions form a family of functions with intriguing modular properties and connections to mock modular forms. In this paper, we take the first step towards investigating modular transformations of higher rank false theta…

Number Theory · Mathematics 2021-08-27 Kathrin Bringmann , Jonas Kaszian , Antun Milas , Caner Nazaroglu

Nazarov-Treil-Volberg recently proved an elegant two-weight T1 theorem for "almost diagonal" operators that played a key role in the proof of the $A_2$ conjecture for dyadic shifts and related operators. In this paper, we obtain a…

Classical Analysis and ODEs · Mathematics 2016-10-10 Kelly Bickel , Brett D. Wick

G\v avruta studied atomic systems in terms of frames for range of operators (that is, for subspaces), namely $K$-frames, where the lower frame condition is controlled by the Hilbert-adjoint of a bounded linear operator $K$. For a locally…

Functional Analysis · Mathematics 2023-02-09 Jyoti , Lalit Kumar Vashisht , Uttam Kumar Sinha

We discuss variants of construction of measurable subgradients for multivariate convex functions and the problem of characterization of the $\Delta_2$-condition in terms of their directional derivatives. Furthermore we study related basic…

Functional Analysis · Mathematics 2026-04-15 Sergey G. Bobkov , Friedrich Götze

Any Z_2-graded C*-dynamical system with a self-adjoint graded-KMS functional on it can be represented (canonically) as a Z_2-graded algebra of bounded operators on a Z_2-graded Hilbert space, so that the grading of the latter is compatible…

Mathematical Physics · Physics 2008-11-26 Orlin Stoytchev

We introduce two kinds of quasi-inner functions. Since every rationally invariant subspace for a shift operator $S_K$ on a vector-valued Hardy space $H^{2}(\Omega,K)$ is generated by a quasi-inner function, we also provide relationships of…

Functional Analysis · Mathematics 2008-01-03 Yun-Su Kim

\v{C}u\v{c}kovi\'{c} and Paudyal recently characterized the lattice of invariant subspaces of the shift plus a complex Volterra operator on the Hilbert space $H^2$ on the unit disk. Motivated by the idea of Ong, in this paper, we give a…

Complex Variables · Mathematics 2018-05-04 Qingze Lin

We review recent interactions between mathematical theory of two-dimensional topological order and operator algebras, particularly the Jones theory of subfactors. The role of representation theory in terms of tensor categories is…

Mathematical Physics · Physics 2021-08-02 Yasuyuki Kawahigashi

The numerical range of a bounded, linear operator on a Hilbert space is a set in $\mathbb{C}$ that encodes important information about the operator. In this survey paper, we first consider numerical ranges of matrices and discuss several…

Functional Analysis · Mathematics 2018-10-30 Kelly Bickel , Pamela Gorkin

In this paper we consider compressions of $k^{th}$--order slant Toeplitz operators to the backward shift invariant subspaces of the classical Hardy space $H^2$. In particular, we characterize these operators using compressed shifts and…

Functional Analysis · Mathematics 2019-11-12 Bartosz Łanucha , Małgorzata Michalska

We notice that for any positive integer $k$, the set of $(1,2)$-specialized characters of level $k$ standard $A_{1}^{(1)}$-modules is the same as the set of rescaled graded dimensions of the subspaces of level $2k+1$ standard…

Quantum Algebra · Mathematics 2007-05-23 Julius Borcea

In this paper the properties of right invertible row operators, i.e., of 1X2 surjective operator matrices are studied. This investigation is based on a specific space decomposition. Using this decomposition, we characterize the…

Functional Analysis · Mathematics 2016-04-12 Junjie Huang , Junfeng Sun , Alatancang Chen , Carsten Trunk

For a matrix-valued function $\Phi\in L^2_{M_{n\times m}}$, it is well-known that the kernel of a block Hankel operator $H_\Phi$ is an invariant subspace for the shift operator. Thus, if the kernel is nontrivial, then $\ker H_\Phi= \Theta…

Functional Analysis · Mathematics 2018-05-03 Dong-O Kang

The purpose of this paper is to generalize Zhu's theorem about characters of modules over a vertex operator algebra graded by integer conformal weights, to the setting of a vertex operator superalgebra graded by rational conformal weights.…

Representation Theory · Mathematics 2013-07-19 Jethro van Ekeren

Let $\theta$ be an inner function satisfying the connected level set condition of B. Cohn, and let $K^{1}_{\theta}$ be the shift-coinvariant subspace of the Hardy space $H^1$ generated by $\theta$. We describe the dual space to…

Complex Variables · Mathematics 2022-02-28 R. V. Bessonov

We introduce and systematically study a class of operators that arise naturally due to the Beurling decomposition of the Hardy space $H^2=K_\theta \oplus \theta H^2$. While the compressions of classical Toeplitz and Hankel operators to the…

Functional Analysis · Mathematics 2026-04-02 Priyanka Aroda , Arup Chattopadhyay , Supratim Jana

In this paper, we investigate the structure of doubly commuting submodules and quotient modules of the Hardy space $H^2(\triangle_H)$ over the Hartogs triangle. We establish a complete classification of doubly commuting submodules. In…

Functional Analysis · Mathematics 2025-08-07 Arup Chattopadhyay , Saikat Giri , Shubham Jain

This work presents a rigorous characterization of inner products on the Hilbert space $S_2$ of Hilbert--Schmidt operators. We first deal with a general setting of continuous sesquilinear forms on a Hilbert space $\mathcal H$, and provide a…

Functional Analysis · Mathematics 2025-06-06 Josué I. Rios-Cangas

Given Hilbert spaces $H_1,H_2,H_3$, we consider bilinear maps defined on the cartesian product $S^2(H_2,H_3)\times S^2(H_1,H_2)$ of spaces of Hilbert-Schmidt operators and valued in either the space $B(H_1,H_3)$ of bounded operators, or in…

Operator Algebras · Mathematics 2020-07-09 Christian Le Merdy , Ivan G. Todorov , Lyudmila Turowska