The composition operators on H-2(D) with minimal polynomial z(n) - 1 are shown to be block Toeplitz with Toeplitz symbol equal to an n x n matrix-valued polynomial of degree 1. This result is used to prove that the numerical range of a composition operator on H-2(D) with minimal polynomial z(3) - 1 cannot be a circular disk. (C) 2012 Elsevier Inc. All rights reserved.
机构:
Sungkyunkwan Univ, Dept Math, Suwon 440746, South KoreaSungkyunkwan Univ, Dept Math, Suwon 440746, South Korea
Hwang, In Sung
Kim, Sumin
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Hanyang Univ, Dept Math, Seoul 04763, South Korea
Hanyang Univ, Res Inst Nat Sci, Seoul 04769, South KoreaSungkyunkwan Univ, Dept Math, Suwon 440746, South Korea
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Tel Aviv Univ, Raymond & Beverly Sackler Fac Exact Sci, Sch Math Sci, IL-69978 Ramat Aviv, IsraelTel Aviv Univ, Raymond & Beverly Sackler Fac Exact Sci, Sch Math Sci, IL-69978 Ramat Aviv, Israel