Invertibility and positivity of truncated Toeplitz operators on certain model subspaces of the Hardy space

2018 ◽  
Vol 118A (2) ◽  
pp. 71-82
Author(s):  
Krishna Subedi ◽  
Anthony Vasaturo
Keyword(s):  
Hardy Space ◽  
Toeplitz Operators ◽  
Model Subspaces

scholarly journals Hyponormal Toeplitz operators on H2(T) with polynomial symbols

1996 ◽  
Vol 144 ◽  
pp. 179-182 ◽  
Author(s):  
Dahai Yu
Keyword(s):  
Functional Equation ◽  
Hardy Space ◽  
Closed Form ◽  
Unit Circle ◽  
Toeplitz Operator ◽  
Explicit Expression ◽  
Complex Plane ◽  
Toeplitz Operators ◽  
Computing Process

Let T be the unit circle on the complex plane, H2(T) be the usual Hardy space on T, Tø be the Toeplitz operator with symbol Cowen showed that if f1 and f2 are functions in H such that is in Lø, then Tf is hyponormal if and only if for some constant c and some function g in H∞ with Using it, T. Nakazi and K. Takahashi showed that the symbol of hyponormal Toeplitz operator Tø satisfies and and they described the ø solving the functional equation above. Both of their conditions are hard to check, T. Nakazi and K. Takahashi remarked that even “the question about polynomials is still open” [2]. Kehe Zhu gave a computing process by way of Schur’s functions so that we can determine any given polynomial ø such that Tø is hyponormal [3]. Since no closed-form for the general Schur’s function is known, it is still valuable to find an explicit expression for the condition of a polynomial á such that Tø is hyponormal and depends only on the coefficients of ø, here we have one, it is elementary and relatively easy to check. We begin with the most general case and the following Lemma is essential.

scholarly journals The wandering subspace property and Shimorin’s condition of shift operator on the weighted Bergman spaces

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Changhui Wu ◽  
Zhijie Wang ◽  
Tao Yu
Keyword(s):  
Hardy Space ◽  
Toeplitz Operators ◽  
Shift Operator ◽  
Bergman Spaces ◽  
Invariant Subspaces ◽  
Weighted Bergman Spaces ◽  
Wandering Subspace ◽  
Formula Type

AbstractIn the present paper, we first study the wandering subspace property of the shift operator on the $$I_{a}$$ I a type zero based invariant subspaces of the weighted Bergman spaces $$L_{a}^{2}(dA_{n})(n=0,2)$$ L a 2 ( d A n ) ( n = 0 , 2 ) via the spectrum of some Toeplitz operators on the Hardy space $$H^{2}$$ H 2 . Second, we give examples to show that Shimorin’s condition for the shift operator fails on the $$I_{a}$$ I a type zero based invariant subspaces of the weighted Bergman spaces $$L_{a}^{2}(dA_{\alpha })(\alpha >0)$$ L a 2 ( d A α ) ( α > 0 ) .

scholarly journals Nearly Invariant Subspaces with Applications to Truncated Toeplitz Operators

2020 ◽  
Vol 14 (8) ◽  
Author(s):  
Ryan O’Loughlin
Keyword(s):  
Hardy Space ◽  
Toeplitz Operator ◽  
Invariant Subspace ◽  
Toeplitz Operators ◽  
Invariant Subspaces ◽  
Decomposition Theorem ◽  
Truncated Toeplitz Operator ◽  
Finite Defect ◽  
Vector Valued

AbstractIn this paper we first study the structure of the scalar and vector-valued nearly invariant subspaces with a finite defect. We then subsequently produce some fruitful applications of our new results. We produce a decomposition theorem for the vector-valued nearly invariant subspaces with a finite defect. More specifically, we show every vector-valued nearly invariant subspace with a finite defect can be written as the isometric image of a backwards shift invariant subspace. We also show that there is a link between the vector-valued nearly invariant subspaces and the scalar-valued nearly invariant subspaces with a finite defect. This is a powerful result which allows us to gain insight in to the structure of scalar subspaces of the Hardy space using vector-valued Hardy space techniques. These results have far reaching applications, in particular they allow us to develop an all encompassing approach to the study of the kernels of: the Toeplitz operator, the truncated Toeplitz operator, the truncated Toeplitz operator on the multiband space and the dual truncated Toeplitz operator.

Admissible Majorants for Model Subspaces of H2, Part I: Slow Winding of the Generating Inner Function

2003 ◽  
Vol 55 (6) ◽  
pp. 1231-1263 ◽  
Author(s):  
Victor Havin ◽  
Javad Mashreghi
Keyword(s):  
Hardy Space ◽  
Half Plane ◽  
Blaschke Product ◽  
Inner Function ◽  
Rate Of Growth ◽  
Model Subspaces ◽  
Almost Everywhere ◽  
Model Subspace ◽  
Upper Half Plane

AbstractA model subspace Kϴ of the Hardy space H2 = H2(ℂ+) for the upper half plane ℂ+ is H2(ℂ+) ϴ ϴH2(ℂ+) where ϴ is an inner function in ℂ+. A function ω: ⟼ [0,∞) is called an admissible majorant for Kϴ if there exists an f ∈ Kϴ, f ≢ 0, |f(x)| ≤ ω(x) almost everywhere on ℝ. For some (mainly meromorphic) ϴ's some parts of Adm ϴ (the set of all admissible majorants for Kϴ) are explicitly described. These descriptions depend on the rate of growth of argϴ along ℝ. This paper is about slowly growing arguments (slower than x). Our results exhibit the dependence of Adm B on the geometry of the zeros of the Blaschke product B. A complete description of Adm B is obtained for B's with purely imaginary (“vertical”) zeros. We show that in this case a unique minimal admissible majorant exists.

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