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The Aluthge transform of unilateral weighted shifts and the Square Root Problem for finitely atomic measures
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The Aluthge transform of unilateral weighted shifts and the Square Root Problem for finitely atomic measures

Raul E Curto, Jaewoong Kim and Jasang Yoon
Mathematische Nachrichten, Vol.292(11), pp.2352-2368
11/01/2019
DOI: 10.1002/mana.201800140

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Abstract

In this paper we consider the following Square Root Problem for measures: Given a positive probability Borel measure mu (supported on an interval [a,b]subset of R+), does there exist a positive Borel measure nu such that mu=nu*nu holds? (Here * denotes the multiplicative convolution, properly defined on R+.) This problem is intimately connected to the subnormality of the Aluthge transform of a unilateral weighted shift. We develop a criterion to test whether a measure mu admits a square root, and we provide a concrete solution for the case of a finitely atomic measure having at most five atoms. In addition, we sharpen the statement of a previous result on this topic and extend its applicability via a new technique that uses the standard inequality of real numbers to generate a diagram of a partial order on the support of a probability measure.
Mathematics Physical Sciences Science & Technology

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