<p>Let <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\( \mathbb {B}(\mathscr {H})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> represent the <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(C^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>C</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-algebra, which consists of all bounded linear operators on <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathscr {H},\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">H</mi> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> and let <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(N ( \cdot ) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>N</mi> <mo stretchy="false">(</mo> <mo>·</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be a norm on <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\( \mathbb {B}(\mathscr {H})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. We define a norm <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(w_{(N,e)} (\cdot , \cdot )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>w</mi> <mrow> <mo stretchy="false">(</mo> <mi>N</mi> <mo>,</mo> <mi>e</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mo>·</mo> <mo>,</mo> <mo>·</mo> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> on <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\( \mathbb {B}^2(\mathscr {H})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi mathvariant="double-struck">B</mi> </mrow> <mn>2</mn> </msup> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> by <Equation ID="Equ13"> <EquationSource Format="TEX">\(\begin{aligned} w_{(N,e)}(B,C)=\underset{|\lambda _1|^2+|\lambda _2|^2\le 1}{\sup }\underset{\theta \in \mathbb {R}}{\sup }N\left( \Re \left( e^{i\theta }(\lambda _1B+\lambda _2C)\right) \right) \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi>w</mi> <mrow> <mo stretchy="false">(</mo> <mi>N</mi> <mo>,</mo> <mi>e</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mi>B</mi> <mo>,</mo> <mi>C</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <munder> <mo movablelimits="false">sup</mo> <mrow> <mrow> <mo stretchy="false">|</mo> </mrow> <msub> <mi>λ</mi> <mn>1</mn> </msub> <msup> <mrow> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo stretchy="false">|</mo> <msub> <mi>λ</mi> <mn>2</mn> </msub> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mo>≤</mo> <mn>1</mn> </mrow> </munder> <munder> <mo movablelimits="false">sup</mo> <mrow> <mi>θ</mi> <mo>∈</mo> <mi mathvariant="double-struck">R</mi> </mrow> </munder> <mi>N</mi> <mfenced close=")" open="("> <mi>ℜ</mi> <mfenced close=")" open="("> <msup> <mi>e</mi> <mrow> <mi>i</mi> <mi>θ</mi> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mi>B</mi> <mo>+</mo> <msub> <mi>λ</mi> <mn>2</mn> </msub> <mi>C</mi> <mo stretchy="false">)</mo> </mrow> </mfenced> </mfenced> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>for every <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(B,C\in \mathbb {B}(\mathscr {H})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>B</mi> <mo>,</mo> <mi>C</mi> <mo>∈</mo> <mi mathvariant="double-struck">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="script">H</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\lambda _1,\lambda _2\in \mathbb {C}.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>λ</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>λ</mi> <mn>2</mn> </msub> <mo>∈</mo> <mi mathvariant="double-struck">C</mi> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> We investigate basic properties of this norm and prove some bounds involving it. In particular, when <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(N( \cdot )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>N</mi> <mo stretchy="false">(</mo> <mo>·</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is the Hilbert-Schmidt norm, we prove some Hilbert-Schmidt Euclidean operator radius bounds for a pair of bounded linear operators.</p>

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Generalized Euclidean operator radius inequalities of a pair of bounded linear operators

  • Suvendu Jana

摘要

Let \( \mathbb {B}(\mathscr {H})\) B ( H ) represent the \(C^*\) C -algebra, which consists of all bounded linear operators on \(\mathscr {H},\) H , and let \(N ( \cdot ) \) N ( · ) be a norm on \( \mathbb {B}(\mathscr {H})\) B ( H ) . We define a norm \(w_{(N,e)} (\cdot , \cdot )\) w ( N , e ) ( · , · ) on \( \mathbb {B}^2(\mathscr {H})\) B 2 ( H ) by \(\begin{aligned} w_{(N,e)}(B,C)=\underset{|\lambda _1|^2+|\lambda _2|^2\le 1}{\sup }\underset{\theta \in \mathbb {R}}{\sup }N\left( \Re \left( e^{i\theta }(\lambda _1B+\lambda _2C)\right) \right) \end{aligned}\) w ( N , e ) ( B , C ) = sup | λ 1 | 2 + | λ 2 | 2 1 sup θ R N e i θ ( λ 1 B + λ 2 C ) for every \(B,C\in \mathbb {B}(\mathscr {H})\) B , C B ( H ) and \(\lambda _1,\lambda _2\in \mathbb {C}.\) λ 1 , λ 2 C . We investigate basic properties of this norm and prove some bounds involving it. In particular, when \(N( \cdot )\) N ( · ) is the Hilbert-Schmidt norm, we prove some Hilbert-Schmidt Euclidean operator radius bounds for a pair of bounded linear operators.