Geodesic
Subnormal n-th roots of matricially and spherically quasinormal pairs
Filomat, Tome 37 (2023) no. 16, p. 5325

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DOI

In a recent paper, Curto et al. [4] asked the following question: " Let T be a subnormal operator, and assume that T 2 is quasinormal. Does it follow that T is quasinormal? ". Pietrzycki and Stochel have answered this question in the affirmative [18] and proved an even stronger result. Namely, the authors have showed that the subnormal n-th roots of a quasinormal operator must be quasinormal. In the present paper, using an elementary technique, we present a much simpler proof of this result and generalize some other results from [4]. We also show that we can relax a condition in the definition of matricially quasinormal n-tuples and we give a correction for one of the results from [4]. Finally, we give sufficient conditions for the equivalence of matricial and spherical quasinormality of T (n,n) := (T n 1 , T n 2) and matricial and spherical quasinormality of T = (T 1 , T 2), respectively.
DOI : 10.2298/FIL2316325S
Classification : 47B20, 47B37, 47A13
Keywords: Subnormal operators, Quasinormal operators, Spherically quasinormal pairs, Matricially quasinormal pairs, (Jointly) quasinormal pairs 
Hranislav Stanković. Subnormal n-th roots of matricially and spherically quasinormal pairs. Filomat, Tome 37 (2023) no. 16, p. 5325 . doi: 10.2298/FIL2316325S
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     title = {Subnormal n-th roots of matricially and spherically quasinormal pairs},
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