$q$-Numerical radius of sectorial matrices and $2 \times 2$ operator matrices

TL;DR

This paper establishes new bounds and relations for the $q$-numerical radius of sectorial matrices and $2 imes 2$ operator matrices, extending previous results and providing practical estimations.

Contribution

It introduces refined bounds for the $q$-numerical radius of sectorial matrices, including bounds for off-diagonal $2 imes 2$ operator matrices and relations for non-integer powers.

Findings

Derived bounds for $w_q(A)$ involving matrix norms and sectorial angle.

Established bounds for commutator and anti-commutator matrices.

Provided estimations for $q$-numerical radius of off-diagonal $2 imes 2$ matrices.

Abstract

This article focuses on several significant bounds of $q$-numerical radius $w_q(A)$ for sectorial matrix $A$ which refine and generalize previously established bounds. One of the significant bounds we have derived is as follows: \[\frac{|q|^2\cos^2\alpha}{2} \|A^*A+AA^*\| \le w_q^2(A)\le \frac{\left(\sqrt{(1-|q|^2)\left(1+2sin^2(\alpha)\right)}+ |q|\right)^2}{2} \|A^*A+AA^*\|,\] where $ A $ is a sectorial matrix. Also, upper bounds for commutator and anti-commutator matrices and relations between $w_q(A^t)$ and $w_q^t(A)$ for non-integral power $t\in [0,1]$ are also obtained. Moreover, a few significant estimations of $q$-numerical radius of off-diagonal $2\times2$ operator matrices are developed.