Hyponormal operators with rank-two self-commutators |
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Authors: | Sang Hoon Lee Woo Young Lee |
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Institution: | a Department of Mathematics, Chungnam National University, Daejeon 305-764, Republic of Korea b Department of Mathematics, Seoul National University, Seoul 151-742, Republic of Korea |
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Abstract: | In this paper it is shown that if T∈L(H) satisfies- (i)
- T is a pure hyponormal operator;
- (ii)
- T∗,T] is of rank two; and
- (iii)
- kerT∗,T] is invariant for T,
then T is either a subnormal operator or the Putinar's matricial model of rank two. More precisely, if T|kerT∗,T] has a rank-one self-commutator then T is subnormal and if instead T|kerT∗,T] has a rank-two self-commutator then T is either a subnormal operator or the kth minimal partially normal extension, , of a (k+1)-hyponormal operator Tk which has a rank-two self-commutator for any k∈Z+. Hence, in particular, every weakly subnormal (or 2-hyponormal) operator with a rank-two self-commutator is either a subnormal operator or a finite rank perturbation of a k-hyponormal operator for any k∈Z+. |
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Keywords: | Hyponormal operators Finite rank self-commutators Subnormal operators Weakly subnormal operators |
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