English

Numerical radius in Hilbert $C^*$-modules

Functional Analysis 2021-12-01 v2

Abstract

Utilizing the linking algebra of a Hilbert CC^*-module (V, ⁣ ⁣)\big(\mathscr{V}, {\|\!\cdot\!\|}\big), we introduce Ω(x)\Omega(x) as a definition of numerical radius for an element xVx\in\mathscr{V} and then show that Ω()\Omega(\cdot) is a norm on V\mathscr{V} such that 12xΩ(x)x\frac{1}{2}{\|x\|} \leq \Omega(x) \leq {\|x\|}. In addition, we obtain an equivalent condition for Ω(x)=12x\Omega(x) = \frac{1}{2}{\|x\|}. Moreover, we present a refinement of the triangle inequality for the norm Ω()\Omega(\cdot). Some other related results are also discussed.

Keywords

Cite

@article{arxiv.2101.04396,
  title  = {Numerical radius in Hilbert $C^*$-modules},
  author = {Ali Zamani},
  journal= {arXiv preprint arXiv:2101.04396},
  year   = {2021}
}

Comments

13 pages

R2 v1 2026-06-23T22:03:43.953Z