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Numerical radius inequalities and estimation of zeros of polynomials

  • Pintu Bhunia , Suvendu Jana and Kallol Paul EMAIL logo
Published/Copyright: June 27, 2023
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Abstract

Let A be a bounded linear operator defined on a complex Hilbert space and let | A | = ( A * A ) 1 2 . Among other refinements of the well-known numerical radius inequality w 2 ( A ) 1 2 A * A + A A * , we show that

w 2 ( A ) 1 4 w 2 ( | A | + i | A * | ) + 1 8 | A | 2 + | A * | 2 + 1 4 w ( | A | | A * | ) 1 2 A * A + A A * .

Also, we develop inequalities involving the numerical radius and the spectral radius for the sum of the product operators, from which we derive the inequalities

w p ( A ) 1 2 w ( | A | p + i | A * | p ) A p

for all p 1 . Further, we derive new bounds for the zeros of complex polynomials.

Funding statement: Dr. Pintu Bhunia would like to thank SERB, Government of India for the financial support in the form of National Post Doctoral Fellowship (N-PDF, File No. PDF/2022/000325) under the mentorship of Professor Apoorva Khare.

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Received: 2022-11-27
Revised: 2023-02-17
Accepted: 2023-03-20
Published Online: 2023-06-27
Published in Print: 2023-10-01

© 2023 Walter de Gruyter GmbH, Berlin/Boston

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