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$A$-Davis-Wielandt Radius Bounds of Semi-Hilbertian Space Operators (2407.21639v1)

Published 31 Jul 2024 in math.FA

Abstract: Consider $\mathcal{H}$ is a complex Hilbert space and $A$ is a positive operator on $\mathcal{H}.$ The mapping $\langle\cdot,\cdot\rangle_A: \mathcal{H}\times \mathcal{H} \to \mathbb {C}$, defined as $\left\langle y,z\right\rangle_{A}=\left\langle Ay,z\right\rangle $ for all $y,z$ $\in $ ${\mathcal{H}}$, induces a seminorm $ \left\Vert \cdot\right\Vert_{A}$. The $A$-Davis-Wielandt radius of an operator $S$ on $\mathcal{H}$ is defined as $d\omega_{A}\left( S\right) =\sup \left{ \sqrt{\left\vert \left\langle Sz,z\right\rangle_{A}\right\vert {2}+\left\Vert Sz\right\Vert_{A}{4}} :\left\Vert z\right\Vert_{A}=1\right} \text{.} $ We investigate some new bounds for $d\omega_{A}\left( S\right)$ which refine the existing bounds. We also give some bounds for the $2\times 2$ off-diagonal block matrices.

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