<p>This work aims to introduce a new Buzano-type inequality that integrates and unifies several well-established results from the literature. As a consequence, we present novel numerical radius bounds for operators in semi-Hilbertian spaces. For example, it is proven that for <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_901_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="83" /> </InlineMediaObject> <EquationSource Format="TEX">\(T \in \mathcal {L}_{A}(\mathcal {H})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mo>∈</mo> <msub> <mi mathvariant="script">L</mi> <mi>A</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and a mapping <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_901_Article_IEq2.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="152" /> </InlineMediaObject> <EquationSource Format="TEX">\(\chi : [0,1]\subset J \rightarrow [\frac{1}{4},1]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>:</mo> <mrow> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> <mo>⊂</mo> <mi>J</mi> <mo stretchy="false">→</mo> <mrow> <mo stretchy="false">[</mo> <mfrac> <mn>1</mn> <mn>4</mn> </mfrac> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, <Equation ID="Equ31"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_901_Article_Equ31.gif" Format="GIF" Height="38" Rendition="HTML" Resolution="72" Type="Linedraw" Width="520" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \omega _{A}^{4}(T) \leqslant \frac{\chi (\lambda )}{4}\left\| T^{\sharp _{A}} T+TT^{\sharp _{A}}\right\| _{A}^{2}+\frac{(1-\chi (\lambda ))}{2}\left\| T^{\sharp _{A}} T+T T^{\sharp _{A}}\right\| _{A} \omega _{A}\left( T^{2}\right) . \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msubsup> <mi>ω</mi> <mrow> <mi>A</mi> </mrow> <mn>4</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> <mo>⩽</mo> <mfrac> <mrow> <mi>χ</mi> <mo stretchy="false">(</mo> <mi>λ</mi> <mo stretchy="false">)</mo> </mrow> <mn>4</mn> </mfrac> <msubsup> <mfenced close="∥" open="∥"> <msup> <mi>T</mi> <msub> <mo>♯</mo> <mi>A</mi> </msub> </msup> <mi>T</mi> <mo>+</mo> <mi>T</mi> <msup> <mi>T</mi> <msub> <mo>♯</mo> <mi>A</mi> </msub> </msup> </mfenced> <mrow> <mi>A</mi> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <mfrac> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>χ</mi> <mo stretchy="false">(</mo> <mi>λ</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </mfrac> <msub> <mfenced close="∥" open="∥"> <msup> <mi>T</mi> <msub> <mo>♯</mo> <mi>A</mi> </msub> </msup> <mi>T</mi> <mo>+</mo> <mi>T</mi> <msup> <mi>T</mi> <msub> <mo>♯</mo> <mi>A</mi> </msub> </msup> </mfenced> <mi>A</mi> </msub> <msub> <mi>ω</mi> <mi>A</mi> </msub> <mfenced close=")" open="("> <msup> <mi>T</mi> <mn>2</mn> </msup> </mfenced> <mo>.</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>Additionally, we establish several bounds for the <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_901_Article_IEq3.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="12" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {A}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">A</mi> </math></EquationSource> </InlineEquation>-numerical radii of <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_901_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="39" /> </InlineMediaObject> <EquationSource Format="TEX">\(2 \times 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>×</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> operator matrices. Our results extend and improve certain well-established inequalities from existing literature.</p>

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Further A-numerical radius inequalities for semi-Hilbertian space operators

  • Abdelmajid Gourty,
  • Mohamed Amine Ighachane,
  • Fuad Kittaneh

摘要

This work aims to introduce a new Buzano-type inequality that integrates and unifies several well-established results from the literature. As a consequence, we present novel numerical radius bounds for operators in semi-Hilbertian spaces. For example, it is proven that for \(T \in \mathcal {L}_{A}(\mathcal {H})\) T L A ( H ) and a mapping \(\chi : [0,1]\subset J \rightarrow [\frac{1}{4},1]\) χ : [ 0 , 1 ] J [ 1 4 , 1 ] , \(\begin{aligned} \omega _{A}^{4}(T) \leqslant \frac{\chi (\lambda )}{4}\left\| T^{\sharp _{A}} T+TT^{\sharp _{A}}\right\| _{A}^{2}+\frac{(1-\chi (\lambda ))}{2}\left\| T^{\sharp _{A}} T+T T^{\sharp _{A}}\right\| _{A} \omega _{A}\left( T^{2}\right) . \end{aligned}\) ω A 4 ( T ) χ ( λ ) 4 T A T + T T A A 2 + ( 1 - χ ( λ ) ) 2 T A T + T T A A ω A T 2 . Additionally, we establish several bounds for the \(\mathbb {A}\) A -numerical radii of \(2 \times 2\) 2 × 2 operator matrices. Our results extend and improve certain well-established inequalities from existing literature.