<p>In this article, we prove a structure theorem for unbounded operator valued local completely contractive map <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\psi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ψ</mi> </math></EquationSource> </InlineEquation> defined on a unital locally <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(C^{*}\)</EquationSource> <EquationSource Format="MATHML"><math> <mmultiscripts> <mi>C</mi> <mrow /> <mrow> <mrow /> <mo>∗</mo> </mrow> </mmultiscripts> </math></EquationSource> </InlineEquation>-algebra <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathcal {A}.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> There is a unique commutant operator <i>T</i> in the structure of <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\psi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ψ</mi> </math></EquationSource> </InlineEquation> with norm at most 2. We show that the operator <i>T</i> is a contraction if and only if the block map <Equation ID="Equ37"> <EquationSource Format="TEX">\(\begin{aligned} \Phi =\begin{bmatrix} \varphi &amp; \psi \\ \psi ^{*} &amp; \varphi \end{bmatrix} \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <mi mathvariant="normal">Φ</mi> <mo>=</mo> <mfenced close="]" open="["> <mrow> <mtable> <mtr> <mtd> <mi>φ</mi> </mtd> <mtd> <mi>ψ</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mmultiscripts> <mi>ψ</mi> <mrow /> <mrow> <mrow /> <mo>∗</mo> </mrow> </mmultiscripts> </mrow> </mtd> <mtd> <mi>φ</mi> </mtd> </mtr> </mtable> </mrow> </mfenced> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>is local completely positive, for some local completely positive and local completely contractive map <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\varphi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>φ</mi> </math></EquationSource> </InlineEquation> on <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\mathcal {A}.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">A</mi> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> In general, such a map <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\varphi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>φ</mi> </math></EquationSource> </InlineEquation> may not exist for a given <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\psi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ψ</mi> </math></EquationSource> </InlineEquation>, we illustrate this situation with an example. However, we prove a block representation of <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\psi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ψ</mi> </math></EquationSource> </InlineEquation> in the sense that there always exist a local completely positive and local completely bounded map <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\varphi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>φ</mi> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\Phi \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Φ</mi> </math></EquationSource> </InlineEquation> is a local completely positive map.</p>

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A structure theorem for local completely contractive maps

  • Santhosh Kumar Pamula,
  • Rifat Siddique

摘要

In this article, we prove a structure theorem for unbounded operator valued local completely contractive map \(\psi \) ψ defined on a unital locally \(C^{*}\) C -algebra \(\mathcal {A}.\) A . There is a unique commutant operator T in the structure of \(\psi \) ψ with norm at most 2. We show that the operator T is a contraction if and only if the block map \(\begin{aligned} \Phi =\begin{bmatrix} \varphi & \psi \\ \psi ^{*} & \varphi \end{bmatrix} \end{aligned}\) Φ = φ ψ ψ φ is local completely positive, for some local completely positive and local completely contractive map \(\varphi \) φ on \(\mathcal {A}.\) A . In general, such a map \(\varphi \) φ may not exist for a given \(\psi \) ψ , we illustrate this situation with an example. However, we prove a block representation of \(\psi \) ψ in the sense that there always exist a local completely positive and local completely bounded map \(\varphi \) φ such that \(\Phi \) Φ is a local completely positive map.