Integral-type operators between the weighted Lipschitz spaces on a tree　　　　　　　　　　　　　　　
Toshikazu Abe; Takuya Hosokawa
Nihonkai Mathematical Journal, 2021年07月, ［査読有り］

Weighted composition operators acting from the Lipschitz space to the space of bounded functions on a tree
We study the weighted composition operators between the Lipschitz space and the space of bounded functions on the set of vertices of an infinite tree.
We characterize the boundedness, the compactness, and the boundedness from below of weighted composition operators. We also determine the isometric weighted composition operators.
Acta Scientiarum Mathematicarum (Szeged), 2020年04月, ［査読有り］

Weighted composition operators between Hilbert spaces of analytic functions in the operator norm and Hilbert-Schmidt norm topologies
Takuya Hosokawa; Kei Ji Izuchi; Shuichi Ohno, We here investigate the topological structure of the space of weighted composition operators boundedly acting between two Hilbert spaces of analytic functions on the open unit disk, satisfying some natural hypotheses. We will consider the operator norm topology and the Hilbert-Schmidt norm topology respectively. These results will be involved-in the investigation for the explicit cases of the classical Hardy-Hilbert space, the weighted Bergman spaces and the Dirichlet space. Furthermore we will estimate the Hilbert-Schmidt norms of difference of two composition operators acting from the Dirichlet space to the Hardy and the weighted Bergman spaces. (c) 2014 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS, 2015年01月, ［査読有り］

Some remarks on operator equation $C_\varphi = C_\psi X$　　　　　　　　　　　　　　　
Takuya Hosokawa; Michio Seto
Nihonkai Mathematical Journal, 2014年, ［査読有り］

DIFFERENCES OF WEIGHTED COMPOSITION OPERATORS FROM H-infinity TO BLOCH SPACE
Takuya Hosokawa; Shuichi Ohno, We consider the boundedness and compactness of the differences of two weighted composition operators acting from the Banach space of bounded analytic functions on the open unit disk to the Bloch space. In the sequel, we will present some explicit examples to bring our reseach into forcus., MATHEMATICAL SOC REP CHINA
TAIWANESE JOURNAL OF MATHEMATICS, 2012年12月, ［査読有り］

Hilbert-Schmidt differences of composition operators on the Bergman space
Boo Rim Choe; Takuya Hosokawa; Hyungwoon Koo, In the setting of the weighted Bergman space over the unit disk, we characterize Hilbert-Schmidt differences of two composition operators in terms of integrability condition involving pseudohyperbolic distance between the inducing functions. We also show that a linear combination of two composition operators can be Hilbert-Schmidt, except for trivial cases, only when it is essentially a difference. We apply our results to study the topological structure of the space of all composition operators under the Hilbert-Schmidt norm topology. We first characterize components and then provide some sufficient conditions for isolation or for non-isolation., SPRINGER
MATHEMATISCHE ZEITSCHRIFT, 2011年12月, ［査読有り］

DIFFERENCES OF WEIGHTED COMPOSITION OPERATORS ACTING FROM BLOCH SPACE TO H-infinity
Takuya Hosokawa; Shuichi Ohno, We study the boundedness and compactness of the differences of two weighted composition operators acting from the Bloch space B to the space H-infinity of bounded analytic functions on the open unit disk. Such a study has a relationship to the topological structure problem of composition operators on H-infinity. Using this relation, we will estimate the operator norms and the essential norms of the differences of two composition operators acting from B to H-infinity., AMER MATHEMATICAL SOC
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY, 2011年10月, ［査読有り］

Linear Combinations of Composition Operators on the Bloch Spaces
Takuya Hosokawa; Pekka J. Nieminen; Shuichi Ohno, We characterize the compactness of linear combinations of analytic composition operators on the Bloch space. We also study their boundedness and compactness on the little Bloch space., CANADIAN MATHEMATICAL SOC
CANADIAN JOURNAL OF MATHEMATICS-JOURNAL CANADIEN DE MATHEMATIQUES, 2011年08月, ［査読有り］

Differences of weighted composition operators acting from Bloch space to $H^\infty$　　　　　　　　　　　　　　　
Takuya Hosokawa; Sh\^{u}ichi Ohno
Transactions of the American Mathematical Society, 2011年, ［査読有り］

Eigenvalues of Weighted Composition Operators on the Bloch Space
Takuya Hosokawa; Quang Dieu Nguyen, This note discusses eigenvalues of weighted composition operators uC (phi) on the Bloch space. The main result provides a class of uC (phi) for which computation of eigenvalues is possible. We also construct an example of a non-compact operator C (phi) whose eigenvalues can be determined precisely., BIRKHAUSER VERLAG AG
INTEGRAL EQUATIONS AND OPERATOR THEORY, 2010年04月, ［査読有り］

Differences of Weighted Composition Operators on the Bloch Spaces
Takuya Hosokawa, We study the boundedness and the compactness of the differences of weighted composition operators on the Bloch spaces. The results generalize the corresponding results on the single weighted composition operators and on the differences of composition operators., BIRKHAUSER VERLAG AG
COMPLEX ANALYSIS AND OPERATOR THEORY, 2009年12月, ［査読有り］

THE ESSENTIAL NORM OF A WEIGHTED COMPOSITION OPERATOR FROM THE BLOCH SPACE TO H-infinity
Takuya Hosokawa, We express the operator norm of a weighted composition operator which acts from the Bloch space B to H-infinity as the supremum of a quantity involving the weight function, the inducing self-map, and the hyperbolic distance. We also express the essential norm of a weighted composition operator from B to H-infinity as the asymptotic upper bound of the same quantity. Moreover we study the estimate of the essential norm of a weighted composition operator from H-infinity to itself., CAMBRIDGE UNIV PRESS
BULLETIN OF THE AUSTRALIAN MATHEMATICAL SOCIETY, 2009年06月, ［査読有り］

Weighted composition operators on the logarithmic Bloch spaces with iterated weights
Takuya Hosokawa; Nguyen Quang Dieu, 新潟大学
Nihonkai Mathematical Journal, 2009年, ［査読有り］

Extreme points of the closed convex hull of composition operators
Takuya Hosokawa, We study the extreme points of the closed convex hull of the set of all composition operators on the space of bounded analytic functions and the disk algebra. (C) 2008 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS, 2008年11月

Differences of composition operators on the Bloch spaces　　　　　　　　　　　　　　　
Takuya Hosokawa; Sh\^{u}ichi Ohno
Journal of Operator Theory, 2007年04月, ［査読有り］

Topological structures of the sets of composition operators on the Bloch spaces
T Hosokawa; S Ohno, We study properties of the topological sets of composition operators on Bloch and little Bloch spaces in the operator topology. (c) 2005 Elsevier Inc. All rights reserved., ACADEMIC PRESS INC ELSEVIER SCIENCE
JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS, 2006年02月, ［査読有り］

Minimum moduli of weighted composition operators on algebras of analytic functions
Takuya Hosokawa, We study the minimum moduli of weighted composition operators on the disk algebra and the space of bounded analytic functions. © 2006, Department of Mathematics, Tokyo Institute of Technology. All rights reserved.
Kodai Mathematical Journal, 2006年, ［査読有り］

Topological structure of the space of weighted composition operators on H-infinity
T Hosokawa; K Izuchi; S Ohno, We study properties of the topological space of weighted composition operators on the space of bounded analytic functions on the open unit disk in the uniform operator topology. Moreover, we characterize the compactness of differences of two weighted composition operators., BIRKHAUSER VERLAG AG
INTEGRAL EQUATIONS AND OPERATOR THEORY, 2005年12月, ［査読有り］

Essential norms of differences of composition operators on H-infinity
T Hosokawa; K Izuchi, We study essential norms of differences of composition operators on the Banach algebra H-infinity of bounded analytic functions on the unit disk., MATH SOC JAPAN
JOURNAL OF THE MATHEMATICAL SOCIETY OF JAPAN, 2005年07月, ［査読有り］

Chaotic behavior of composition operators on the Hardy space　　　　　　　　　　　　　　　
Takuya Hosokawa
Acta Scientiarum Mathematicarum(Szeged), 2003年, ［査読有り］

Isolated points and essential components of composition operators on H infinity
T Hosokawa; K Izuchi; D Zheng, We consider the topological space of all composition operators on the Banach algebra of bounded analytic functions on the unit disk. We obtain a function theoretic characterization of isolated points and show that each isolated composition operator is essentially isolated., AMER MATHEMATICAL SOC
PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY, 2002年, ［査読有り］

Some operators on power growth spaces on a tree　　　　　　　　　　　　　　　
2021年度関数環研究集会, 2021年12月17日

tree上の関数空間とその上の荷重合成作用素　　　　　　　　　　　　　　　
細川卓也
2020年度関数環研究集会, 2020年11月27日

Weighted composition operators between Bergman spaces　　　　　　　　　　　　　　　
細川卓也
Real, Complex and Functional Analysis Seminar 2019, 2019年11月09日

Composition operators induced by products of analytic self-maps　　　　　　　　　　　　　　　
細川卓也
Spring Central and Western Joint Sectional Meeting of American Mathematical Society, 2019年03月23日, ［招待有り］

Integral operators acting from Bergman spaces to BMOA-type spaces　　　　　　　　　　　　　　　
細川卓也
2018年度関数環研究集会, 2018年11月30日

On some operators on function spaces on trees　　　　　　　　　　　　　　　
細川卓也
Real, Complex and Functional Analysis Seminar 2018, 2018年11月18日

写像の葉数と作用素の挙動について　　　　　　　　　　　　　　　
細川卓也
防大関数解析セミナー, 2018年06月22日

Composition operators with product symbols　　　　　　　　　　　　　　　
細川卓也
Real, Complex and Functional Analysis Seminar 2017, 2017年12月16日

Composition operators with product symbols　　　　　　　　　　　　　　　
細川卓也
第39回東北複素解析セミナー, 2017年11月29日

解析関数空間上の合成作用素の成す集合の位相構造について　　　　　　　　　　　　　　　
細川卓也
関東作用素論セミナー, 2017年05月20日

単位円板上の正則自己写像の積と合成作用素の性質について　　　　　　　　　　　　　　　
細川卓也
つくばセミナー, 2016年03月08日

Composition operators with product symbols　　　　　　　　　　　　　　　
細川卓也
2015年度 関数環研究集会, 2015年12月19日

Weighted composition operators between Hilbert spaces of analytic functions in Hilbert-Schmidt norm topologies　　　　　　　　　　　　　　　
細川卓也
日本数学会２０１５年度秋季総合分科会, 2015年09月15日

Linear combinations of composition operators on H^∞ and the Bloch space　　　　　　　　　　　　　　　
２０１３年作用素論・作用素環論研究集会, 2013年11月24日, ［招待有り］

Differences of weighted composition operators from H∞ to the Bloch space　　　　　　　　　　　　　　　
2013日本数学会秋季総合分科会, 2013年09月25日

Some notes on composition operators on the Bloch space　　　　　　　　　　　　　　　
第21回宮代セミナー, 2012年10月31日

Differences of weighted composition operators from the Bloch space to H∞　　　　　　　　　　　　　　　
2012 日本数学会 秋季総合分科会, 2012年09月20日

Differences of weighted composition operators between H∞ and the Bloch spaces　　　　　　　　　　　　　　　
Functional Analysis Seminar, 2012年08月28日

Eigenvalues of weighted composition operators on the Bloch space　　　　　　　　　　　　　　　
日本数学会2012年会, 2012年03月27日

Linear combinations of composition operators on the Bloch space　　　　　　　　　　　　　　　
日本数学会2012年会, 2012年03月27日

Integral type operators from H∞　　　　　　　　　　　　　　　
2011年度関数環研究集会, 2011年12月02日

Composition operators from H∞ to the little Bloch space　　　　　　　　　　　　　　　
第20回宮代セミナー, 2011年08月18日

Differences of composition operators between H∞ and the Bloch space　　　　　　　　　　　　　　　
2010年度関数環研究集会, 2010年11月30日

Extreme points of the closed convex hull of composition operators on H∞　　　　　　　　　　　　　　　
2010 日本数学会 秋季総合分科会, 2010年09月25日

Norms and essential norms of weighted composition operators between the Bloch space and H∞　　　　　　　　　　　　　　　
2010 日本数学会 秋季総合分科会, 2010年09月25日

Linear combinations of composition operators on H∞ and the Bloch spaces　　　　　　　　　　　　　　　
2009年度関数環研究集会, 2009年11月27日

Differences of weighted composition operators between H∞ and the Bloch space　　　　　　　　　　　　　　　
第52回函数論シンポジウム, 2009年11月21日

Differences of weighted composition operators on the Bloch space　　　　　　　　　　　　　　　
2009 日本数学会 秋季総合分科会, 2009年09月26日

2004年09月, 日本数学会