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Furtherance of Numerical radius inequalities of Hilbert space operators

Functional Analysis 2024-08-14 v1

Abstract

If A,BA,B are bounded linear operators on a complex Hilbert space, then % w(A)12(A+r(AA))w(A) \leq \frac{1}{2}\left( \|A\|+\sqrt{r\left(|A||A^*|\right)}\right) and w(AB±BA)22Bw2(A)c2((A))+c2((A))2,w(AB \pm BA)\leq 2\sqrt{2}\|B\|\sqrt{ w^2(A)-\frac{c^2(\Re (A))+c^2(\Im (A))}{2} }, \begin{eqnarray*} w(A) &\leq& \frac{1}{2}\left( \|A\|+\sqrt{r\left(|A||A^*|\right)}\right),\\ w(AB \pm BA)&\leq& 2\sqrt{2}\|B\|\sqrt{ w^2(A)-\frac{c^2(\Re (A))+c^2(\Im (A))}{2} }, \end{eqnarray*} where w(.),.,c(.)w(.),\|.\|,c(.) and r(.)r(.) are the numerical radius, the operator norm, the Crawford number and the spectral radius respectively, and (A)\Re (A), (A)\Im (A) are the real part, the imaginary part of AA respectively. The inequalities obtained here generalize and improve on the existing well known inequalities.

Keywords

Cite

@article{arxiv.2102.01953,
  title  = {Furtherance of Numerical radius inequalities of Hilbert space operators},
  author = {Pintu Bhunia and Kallol Paul},
  journal= {arXiv preprint arXiv:2102.01953},
  year   = {2024}
}

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9 pages