<p>The Berezin range of a bounded operator <i>A</i> acting on a reproducing kernel Hilbert space <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathscr {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> </InlineEquation> is the set <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq2.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="224" /> </InlineMediaObject> <EquationSource Format="TEX">\({\textbf {Ber}}(A):= \{ \langle A\hat{k}_{\tau },\hat{k}_{\tau }\rangle : \tau \in \Theta \}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="bold">Ber</mi> <mrow> <mo stretchy="false">(</mo> <mi>A</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mo stretchy="false">{</mo> <mrow> <mo stretchy="false">⟨</mo> <mi>A</mi> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</mi> </msub> <mo>,</mo> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</mi> </msub> <mo stretchy="false">⟩</mo> </mrow> <mo>:</mo> <mi>τ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq3.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\hat{k}_{\tau }\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</mi> </msub> </math></EquationSource> </InlineEquation> is the normalized reproducing kernel for <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathscr {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">H</mi> </math></EquationSource> </InlineEquation> at <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq5.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="44" /> </InlineMediaObject> <EquationSource Format="TEX">\(\tau \in \Theta \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>τ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> </mrow> </math></EquationSource> </InlineEquation>. The Berezin radius (number) and the Berezin norm of an operator <i>A</i> are defined by <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq6.gif" Format="GIF" Height="33" Rendition="HTML" Resolution="72" Type="Linedraw" Width="183" /> </InlineMediaObject> <EquationSource Format="TEX">\({\textbf {ber}}\left( A\right) :=\underset{\tau \in \Theta }{\sup }\big \vert \langle {A}\hat{k}_{\tau },\hat{k}_{\tau }\rangle \big \vert \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="bold">ber</mi> <mfenced close=")" open="("> <mi>A</mi> </mfenced> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="false">sup</mo> <mrow> <mi>τ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> </mrow> </munder> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> <mrow> <mo stretchy="false">⟨</mo> <mi>A</mi> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</mi> </msub> <mo>,</mo> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</mi> </msub> <mo stretchy="false">⟩</mo> </mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq7.gif" Format="GIF" Height="35" Rendition="HTML" Resolution="72" Type="Linedraw" Width="189" /> </InlineMediaObject> <EquationSource Format="TEX">\(\left\| A\right\| _{{\textbf {ber}}}:=\underset{\tau ,\mu \in \Theta }{\sup }\big \vert \langle {A}\hat{k}_{\tau },\hat{k}_{\mu }\rangle \big \vert \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mfenced close="∥" open="∥"> <mi>A</mi> </mfenced> <mi mathvariant="bold">ber</mi> </msub> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="false">sup</mo> <mrow> <mi>τ</mi> <mo>,</mo> <mi>μ</mi> <mo>∈</mo> <mi mathvariant="normal">Θ</mi> </mrow> </munder> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> <mrow> <mo stretchy="false">⟨</mo> <mi>A</mi> <msub> <mover accent="true"> <mi>k</mi> <mo stretchy="false">^</mo> </mover> <mi>τ</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 maxsize="1.2em" minsize="1.2em" stretchy="true">|</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, respectively. In this paper, we obtain some estimations for the Berezin radius and the Berezin norm. It is shown, among other inequalities, that if <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(A,B\in {{\mathscr {L}}}({{\mathscr {H}}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>A</mi> <mo>,</mo> <mi>B</mi> <mo>∈</mo> <mi mathvariant="script">L</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq9.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="71" /> </InlineMediaObject> <EquationSource Format="TEX">\(1\le r\le 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>r</mi> <mo>≤</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, then <Equation ID="Equ15"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_Equ15.gif" Format="GIF" Height="120" Rendition="HTML" Resolution="72" Type="Linedraw" Width="392" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} {\textbf {ber}}^r(A^*B)&amp;\le \frac{1}{2^{r\mu } p} {\textbf {ber}}^{r(1-\mu )}(A^*B)\left\| \vert A\vert ^{2}+ \vert B\vert ^{2}\right\| _{\textbf {ber}}^{r\mu }\\&amp;\quad +\frac{1}{2^{r(1-\nu )}q} {\textbf {ber}}^{r\nu }(A^*B) \left\| \vert A\vert ^{2}+ \vert B\vert ^{2}\right\| _{\textbf {ber}}^{r(1-\nu )}\\ &amp;\le \frac{1}{2} \left\| \vert A\vert ^{2r}+ \vert B\vert ^{2r}\right\| _{\textbf {ber}} \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msup> <mrow> <mi mathvariant="bold">ber</mi> </mrow> <mi>r</mi> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mi>A</mi> <mo>∗</mo> </msup> <mi>B</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </mtd> <mtd columnalign="left"> <mrow> <mo>≤</mo> <mfrac> <mn>1</mn> <mrow> <msup> <mn>2</mn> <mrow> <mi>r</mi> <mi>μ</mi> </mrow> </msup> <mi>p</mi> </mrow> </mfrac> <msup> <mrow> <mi mathvariant="bold">ber</mi> </mrow> <mrow> <mi>r</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>μ</mi> <mo stretchy="false">)</mo> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mi>A</mi> <mo>∗</mo> </msup> <mi>B</mi> <mo stretchy="false">)</mo> </mrow> <msubsup> <mfenced close="∥" open="∥"> <msup> <mrow> <mo stretchy="false">|</mo> <mi>A</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo stretchy="false">|</mo> <mi>B</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> </mfenced> <mrow> <mi mathvariant="bold">ber</mi> </mrow> <mrow> <mi>r</mi> <mi>μ</mi> </mrow> </msubsup> </mrow> </mtd> </mtr> <mtr> <mtd columnalign="right"> <mrow /> </mtd> <mtd columnalign="left"> <mrow> <mspace width="1em" /> <mo>+</mo> <mfrac> <mn>1</mn> <mrow> <msup> <mn>2</mn> <mrow> <mi>r</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>ν</mi> <mo stretchy="false">)</mo> </mrow> </msup> <mi>q</mi> </mrow> </mfrac> <msup> <mrow> <mi mathvariant="bold">ber</mi> </mrow> <mrow> <mi>r</mi> <mi>ν</mi> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mi>A</mi> <mo>∗</mo> </msup> <mi>B</mi> <mo stretchy="false">)</mo> </mrow> <msubsup> <mfenced close="∥" open="∥"> <msup> <mrow> <mo stretchy="false">|</mo> <mi>A</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo stretchy="false">|</mo> <mi>B</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> </mfenced> <mrow> <mi mathvariant="bold">ber</mi> </mrow> <mrow> <mi>r</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>ν</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> </mrow> </mtd> </mtr> <mtr> <mtd columnalign="right"> <mrow /> </mtd> <mtd columnalign="left"> <mrow> <mo>≤</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mfenced close="∥" open="∥"> <msup> <mrow> <mo stretchy="false">|</mo> <mi>A</mi> <mo stretchy="false">|</mo> </mrow> <mrow> <mn>2</mn> <mi>r</mi> </mrow> </msup> <mo>+</mo> <msup> <mrow> <mo stretchy="false">|</mo> <mi>B</mi> <mo stretchy="false">|</mo> </mrow> <mrow> <mn>2</mn> <mi>r</mi> </mrow> </msup> </mfenced> <mi mathvariant="bold">ber</mi> </msub> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>for all <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq10.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="83" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mu , \nu \in [0,1]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mo>,</mo> <mi>ν</mi> <mo>∈</mo> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="57" /> </InlineMediaObject> <EquationSource Format="TEX">\(p,q&gt;0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>,</mo> <mi>q</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12215_2025_1234_Article_IEq12.gif" Format="GIF" Height="25" Rendition="HTML" Resolution="72" Type="Linedraw" Width="68" /> </InlineMediaObject> <EquationSource Format="TEX">\(\frac{1}{p}+\frac{1}{q}=1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mfrac> <mn>1</mn> <mi>p</mi> </mfrac> <mo>+</mo> <mfrac> <mn>1</mn> <mi>q</mi> </mfrac> <mo>=</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Some estimations of the Berezin radius and the Berezin norm

  • Mojtaba Bakherad,
  • Fuad Kittaneh

摘要

The Berezin range of a bounded operator A acting on a reproducing kernel Hilbert space \(\mathscr {H}\) H is the set \({\textbf {Ber}}(A):= \{ \langle A\hat{k}_{\tau },\hat{k}_{\tau }\rangle : \tau \in \Theta \}\) Ber ( A ) : = { A k ^ τ , k ^ τ : τ Θ } , where \(\hat{k}_{\tau }\) k ^ τ is the normalized reproducing kernel for \(\mathscr {H}\) H at \(\tau \in \Theta \) τ Θ . The Berezin radius (number) and the Berezin norm of an operator A are defined by \({\textbf {ber}}\left( A\right) :=\underset{\tau \in \Theta }{\sup }\big \vert \langle {A}\hat{k}_{\tau },\hat{k}_{\tau }\rangle \big \vert \) ber A : = sup τ Θ | A k ^ τ , k ^ τ | and \(\left\| A\right\| _{{\textbf {ber}}}:=\underset{\tau ,\mu \in \Theta }{\sup }\big \vert \langle {A}\hat{k}_{\tau },\hat{k}_{\mu }\rangle \big \vert \) A ber : = sup τ , μ Θ | A k ^ τ , k ^ μ | , respectively. In this paper, we obtain some estimations for the Berezin radius and the Berezin norm. It is shown, among other inequalities, that if \(A,B\in {{\mathscr {L}}}({{\mathscr {H}}})\) A , B L ( H ) and \(1\le r\le 2\) 1 r 2 , then \(\begin{aligned} {\textbf {ber}}^r(A^*B)&\le \frac{1}{2^{r\mu } p} {\textbf {ber}}^{r(1-\mu )}(A^*B)\left\| \vert A\vert ^{2}+ \vert B\vert ^{2}\right\| _{\textbf {ber}}^{r\mu }\\&\quad +\frac{1}{2^{r(1-\nu )}q} {\textbf {ber}}^{r\nu }(A^*B) \left\| \vert A\vert ^{2}+ \vert B\vert ^{2}\right\| _{\textbf {ber}}^{r(1-\nu )}\\ &\le \frac{1}{2} \left\| \vert A\vert ^{2r}+ \vert B\vert ^{2r}\right\| _{\textbf {ber}} \end{aligned}\) ber r ( A B ) 1 2 r μ p ber r ( 1 - μ ) ( A B ) | A | 2 + | B | 2 ber r μ + 1 2 r ( 1 - ν ) q ber r ν ( A B ) | A | 2 + | B | 2 ber r ( 1 - ν ) 1 2 | A | 2 r + | B | 2 r ber for all \(\mu , \nu \in [0,1]\) μ , ν [ 0 , 1 ] and \(p,q>0\) p , q > 0 with \(\frac{1}{p}+\frac{1}{q}=1\) 1 p + 1 q = 1 .