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Improved bounds for the numerical radius via a new norm on B(H)

Author : Dr Pintu Bhunia

Year : 2025

Publisher : Walter de Gruyter GmbH

Source Title : Georgian Mathematical Journal

Document Type :

Abstract

In this paper, we introduce a new norm, christened the t-operator norm, on the space of all bounded linear operators defined on a complex Hilbert space H as (Formula Prasented), where x, y ϵ H and t ϵ [ 0, 1 ]. This norm satisfies 1/2 Tt ≤ w (T) ≤ Tt 12 and we explore its properties. This norm characterizes those invertible operators that are also unitary. We obtain various inequalities involving the t-operator norm and the usual operator norm. We show that w (T) ≤ min t ϵ improves the existing bounds w (T) ≤ 1/2 w(T) (see [F. Kittaneh, A numerical radius inequality and an estimate for the numerical radius of the Frobenius companion matrix, Studia Math. 158 2003, 1, 11-17]) and w (T) ≤ 1/2 T ∗ (see [F. Kittaneh, Numerical radius inequalities for Hilbert space operators, Studia Math. 168 2005, 1, 73-80]). We show that (T) ≤ min | λ | = 1 . Further, we study the t-operator norm of operator matrices.