English

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

Functional Analysis 2026-02-04 v1

Abstract

This article focuses on several significant bounds of qq-numerical radius wq(A)w_q(A) for sectorial matrix AA which refine and generalize previously established bounds. One of the significant bounds we have derived is as follows: q2cos2α2AA+AAwq2(A)((1q2)(1+2sin2(α))+q)22AA+AA,\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 A is a sectorial matrix. Also, upper bounds for commutator and anti-commutator matrices and relations between wq(At)w_q(A^t) and wqt(A)w_q^t(A) for non-integral power t[0,1]t\in [0,1] are also obtained. Moreover, a few significant estimations of qq-numerical radius of off-diagonal 2×22\times2 operator matrices are developed.

Keywords

Cite

@article{arxiv.2501.14505,
  title  = {$q$-Numerical radius of sectorial matrices and $2 \times 2$ operator matrices},
  author = {Jyoti Rani and Arnab Patra},
  journal= {arXiv preprint arXiv:2501.14505},
  year   = {2026}
}