<p>In this note, we introduce a novel norm, termed the <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11785_2025_1710_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(t-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>t</mi> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation>Berezin norm, on the algebra of all bounded linear operators defined on a reproducing kernel Hilbert space <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11785_2025_1710_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {H}(\Omega )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">H</mi> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> as <Equation ID="Equ8"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="11785_2025_1710_Article_Equ8.gif" Format="GIF" Height="39" Rendition="HTML" Resolution="72" Type="Linedraw" Width="457" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned}{\Vert A\Vert _{ber}}_t = \sup _{ \lambda , \mu \in \Omega } \left\{ t|\langle A \hat{k}_\lambda , \hat{k}_\mu \rangle | + (1-t) |\langle A^* \hat{k}_\lambda , \hat{k}_\mu \rangle | \right\} , \quad t\in [0,1],\end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mrow> <msub> <mrow> <mo stretchy="false">‖</mo> <mi>A</mi> <mo stretchy="false">‖</mo> </mrow> <mrow> <mi mathvariant="italic">ber</mi> </mrow> </msub> </mrow> <mi>t</mi> </msub> <mo>=</mo> <munder> <mo movablelimits="true">sup</mo> <mrow> <mi>λ</mi> <mo>,</mo> <mi>μ</mi> <mo>∈</mo> <mi mathvariant="normal">Ω</mi> </mrow> </munder> <mfenced close="}" open="{"> <mrow> <mi>t</mi> <mo stretchy="false">|</mo> </mrow> <mrow> <mo stretchy="false">⟨</mo> <mi>A</mi> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>λ</mi> </msub> <mo>,</mo> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>μ</mi> </msub> <mo stretchy="false">⟩</mo> </mrow> <mrow> <mo stretchy="false">|</mo> <mo>+</mo> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mo stretchy="false">|</mo> <mrow> <mo stretchy="false">⟨</mo> <msup> <mi>A</mi> <mo>∗</mo> </msup> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>λ</mi> </msub> <mo>,</mo> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>μ</mi> </msub> <mo stretchy="false">⟩</mo> </mrow> <mo stretchy="false">|</mo> </mrow> </mfenced> <mo>,</mo> <mspace width="1em" /> <mi>t</mi> <mo>∈</mo> <mrow> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11785_2025_1710_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="98" /> </InlineMediaObject> <EquationSource Format="TEX">\(A \in \mathcal {B}(\mathcal {H}(\Omega ))\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>A</mi> <mo>∈</mo> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a bounded linear operator. This norm characterizes those invertible operators which are also unitary. Using this newly defined norm, we establish various upper bounds for the Berezin number, thereby refining the existing results. Additionally, we derive several sharp bounds for the Berezin number of an operator via the Orlicz function.</p>

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A New Norm on the Space of Reproducing Kernel Hilbert Space Operators and Berezin Number Inequalities

  • Raj Kumar Nayak,
  • Pintu Bhunia

摘要

In this note, we introduce a novel norm, termed the \(t-\) t - Berezin norm, on the algebra of all bounded linear operators defined on a reproducing kernel Hilbert space \(\mathcal {H}(\Omega )\) H ( Ω ) as \(\begin{aligned}{\Vert A\Vert _{ber}}_t = \sup _{ \lambda , \mu \in \Omega } \left\{ t|\langle A \hat{k}_\lambda , \hat{k}_\mu \rangle | + (1-t) |\langle A^* \hat{k}_\lambda , \hat{k}_\mu \rangle | \right\} , \quad t\in [0,1],\end{aligned}\) A ber t = sup λ , μ Ω t | A k ^ λ , k ^ μ | + ( 1 - t ) | A k ^ λ , k ^ μ | , t [ 0 , 1 ] , where \(A \in \mathcal {B}(\mathcal {H}(\Omega ))\) A B ( H ( Ω ) ) is a bounded linear operator. This norm characterizes those invertible operators which are also unitary. Using this newly defined norm, we establish various upper bounds for the Berezin number, thereby refining the existing results. Additionally, we derive several sharp bounds for the Berezin number of an operator via the Orlicz function.