Composition Operators and Classical Function Theory

Majee, Satyabarta and D, Venku Naidu (2018) Composition Operators and Classical Function Theory. Masters thesis, Indian Institute of Technology Hyderabad.

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(1) The section Linear Fractional Prologue is a context, to be consulted as needed , on the basic properties and classi�cation of linear fractional transformations. Linear fractional maps play a vital role in my work, both as agents for changing coordinates and transforming settings. (2) In the section Fourier series, I discuss how to construct a inner product from given Fourier series , the Dirichlet Kernel and its properties. Then I give the proof of Plancharal theorem and Parseval's theorem which play a good role through out my project. (3) This Littlewood's Theorem section is most important part of my work. After developing some of the basic properties of H2, here we shows that every composition operator acts boundedly on the Hilbert space. As pointed out above, this is essentially Littlewood's Subordination Principle. I present Littlewood's original proof - a beautiful argument that is perfectly transparent in its beauty, but utterly ba�ing in its lack of geometric insight. Much of conclusion can be regarded as an e�ort to understand the geometric underpinning of this theorem. (4) Having established that every composition operator is bounded on H2, we turn to the most natural follow-up question: "Which composition operators are compact?" The Chapter Compact- ness:Introduction sets out the motivation for this problem. The property of "boundedness" for composition operators means that each one takes bounded subsets of H2 to bounded subsets. The question above asks us to specify precisely how much the inducing map � has to compress the unit disc into itself in order to insure that the operator C� compresses bounded subsets of H2 into relatively compact ones. (5) In Chapter Compactness and Univalence we discover that the geometric soul of Littlewood's Theorem is bound up in the Schwarz Lemma. Armed with this insight, we are able to characterize the univalently induced compact composition operators, obtaining a compactness criterion that leads directly to the Julia-Caratheodory Theorem on the angular derivative. (6) In Chapter The Angular Derivative, I give the idea of the proof of Julia-Caratheodory Theorem in a way that emphasizes its geometric content, especially its connection with the Schwarz Lemma.

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Item Type: Thesis (Masters)
Subjects: Mathematics
Divisions: Department of Mathematics
Depositing User: Team Library
Date Deposited: 20 Jun 2018 10:56
Last Modified: 20 Jun 2018 10:56
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