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A New Family of Semi-Norms Between the Berezin Radius and the Berezin Norm

  • Mojtaba Bakherad,
  • Cristian Conde,
  • Fuad Kittaneh

摘要

A functional Hilbert space is the Hilbert space ℋ of complex-valued functions on some set Θ C $\Theta \subseteq \mathbb{C}$ such that the evaluation functionals φ τ ( f ) = f ( τ ) $\varphi _{\tau }\left ( f\right ) =f\left ( \tau \right ) $ , τ Θ $\tau \in \Theta $ , are continuous on ℋ. The Berezin number of an operator X $X$ is defined by ber ( X ) = sup τ Θ | X ˜ ( τ ) | = sup τ Θ | X k ˆ τ , k ˆ τ | $\mathbf{ber}(X)=\underset{\tau \in {\Theta } }{\sup }\big \vert \widetilde{X}(\tau )\big \vert = \underset{\tau \in {\Theta } }{\sup }\big \vert \langle X\hat{k}_{\tau },\hat{k}_{\tau }\rangle \big \vert $ , where the operator X $X$ acts on the reproducing kernel Hilbert space H = H ( Θ ) ${\mathscr{H}}={\mathscr{H}(}\Theta )$ over some (non-empty) set Θ $\Theta $ . In this paper, we introduce a new family involving means σ t $\Vert \cdot \Vert _{\sigma _{t}}$ between the Berezin radius and the Berezin norm. Among other results, it is shown that if X L ( H ) $X\in {\mathscr{L}}({\mathscr{H}})$ and f $f$ , g $g$ are two non-negative continuous functions defined on [ 0 , ) $[0,\infty )$ such that f ( t ) g ( t ) = t , ( t 0 ) $f(t)g(t) = t,\,(t\geqslant 0)$ , then X σ 2 ber ( 1 4 ( f 4 ( | X | ) + g 4 ( | X | ) ) + 1 2 | X | 2 ) \(\begin{aligned} \Vert X\Vert ^{2}_{\sigma }\leqslant \textbf{ber}\left (\frac{1}{4}(f^{4}( \vert X\vert )+g^{4}(\vert X^{*}\vert ))+\frac{1}{2}\vert X\vert ^{2} \right ) \end{aligned}\) and X σ 2 1 2 ber ( f 4 ( | X | ) + g 2 ( | X | 2 ) ) ber ( f 2 ( | X | 2 ) + g 4 ( | X | ) ) , \(\begin{aligned} \Vert X\Vert ^{2}_{\sigma }\leqslant \frac{1}{2}\sqrt{\textbf{ber} \left (f^{4}(\vert X\vert )+g^{2}(\vert X\vert ^{2})\right ) \textbf{ber}\left (f^{2}(\vert X\vert ^{2})+g^{4}(\vert X^{*}\vert ) \right )}, \end{aligned}\) where σ $\sigma $ is a mean dominated by the arithmetic mean $\nabla $ .