<p>Let <i>X</i> be Banach space. For <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(x\in X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>x</mi> <mo>∈</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\Vert x\Vert =1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">‖</mo> <mi>x</mi> <mo stretchy="false">‖</mo> <mo>=</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, we denote the state space by, <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(S_{x}=\{x^*\in X^*:\Vert x^*\Vert =x^*(x)=1\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>S</mi> <mi>x</mi> </msub> <mrow> <mo>=</mo> <mo stretchy="false">{</mo> </mrow> <msup> <mi>x</mi> <mo>∗</mo> </msup> <mo>∈</mo> <msup> <mi>X</mi> <mo>∗</mo> </msup> <mrow> <mo>:</mo> <mo stretchy="false">‖</mo> </mrow> <msup> <mi>x</mi> <mo>∗</mo> </msup> <mrow> <mo stretchy="false">‖</mo> <mo>=</mo> <msup> <mi>x</mi> <mo>∗</mo> </msup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mn>1</mn> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In this paper, we study <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\hbox {weak}^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mtext>weak</mtext> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-weak and <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\hbox {weak}^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mtext>weak</mtext> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-<InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\Vert .\Vert \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">‖</mo> <mo>.</mo> <mo stretchy="false">‖</mo> </mrow> </math></EquationSource> </InlineEquation> points of continuity of the identity map, on the state spaces in the space <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\ell ^{p}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>ℓ</mi> <mi>p</mi> </msup> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(1&lt;p&lt;\infty \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>&lt;</mo> <mi>p</mi> <mo>&lt;</mo> <mi>∞</mi> </mrow> </math></EquationSource> </InlineEquation> for a non-reflexive Banach space <i>X</i> and then we use these results to characterize the weak and norm compactness of the state spaces of unit vectors in <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\ell ^{p}(X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>ℓ</mi> <mi>p</mi> </msup> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In addition, we address an open problem, the characterization of weakly compact state spaces in the space of Bochner-integrable functions <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(L^{1}(\mu , X)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>L</mi> <mn>1</mn> </msup> <mrow> <mo stretchy="false">(</mo> <mi>μ</mi> <mo>,</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> (see Daptari and Dwivedi in Colloq Math 179(1):87–105, 2025, Problem&#xa0;3.18). We also provide a local solution to this problem without any additional assumptions on the Banach space <i>X</i>. Motivated by the work of Daptari et al. (Rev R Acad Cienc Exactas Fís Nat Ser A Mat 119(3):82, 2025), we show that if the set of all <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(\hbox {weak}^{*}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mtext>weak</mtext> <mrow> <mrow /> <mo>∗</mo> </mrow> </msup> </math></EquationSource> </InlineEquation>-weak points of continuity of <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(L^{1}(\mu , X)_{1}^{*}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>L</mi> <mn>1</mn> </msup> <msubsup> <mrow> <mo stretchy="false">(</mo> <mi>μ</mi> <mo>,</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mn>1</mn> </mrow> <mrow> <mrow /> <mo>∗</mo> </mrow> </msubsup> </mrow> </math></EquationSource> </InlineEquation> is weakly dense in <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(L^{1}(\mu , X)_{1}^{*}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>L</mi> <mn>1</mn> </msup> <msubsup> <mrow> <mo stretchy="false">(</mo> <mi>μ</mi> <mo>,</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mn>1</mn> </mrow> <mrow> <mrow /> <mo>∗</mo> </mrow> </msubsup> </mrow> </math></EquationSource> </InlineEquation>, then <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\(X^{*}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>X</mi> <mrow> <mrow /> <mo>∗</mo> </mrow> </msup> </math></EquationSource> </InlineEquation> has the Radon–Nikodým property (RNP) (see Theorem&#xa0;<InternalRef RefID="FPar38">3.12</InternalRef>).</p>

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\(\hbox {Weak}^*\)-weak points of continuity on the state spaces

  • Saurabh Dwivedi

摘要

Let X be Banach space. For \(x\in X\) x X with \(\Vert x\Vert =1\) x = 1 , we denote the state space by, \(S_{x}=\{x^*\in X^*:\Vert x^*\Vert =x^*(x)=1\}\) S x = { x X : x = x ( x ) = 1 } . In this paper, we study \(\hbox {weak}^*\) weak -weak and \(\hbox {weak}^*\) weak - \(\Vert .\Vert \) . points of continuity of the identity map, on the state spaces in the space \(\ell ^{p}(X)\) p ( X ) for \(1<p<\infty \) 1 < p < for a non-reflexive Banach space X and then we use these results to characterize the weak and norm compactness of the state spaces of unit vectors in \(\ell ^{p}(X)\) p ( X ) . In addition, we address an open problem, the characterization of weakly compact state spaces in the space of Bochner-integrable functions \(L^{1}(\mu , X)\) L 1 ( μ , X ) (see Daptari and Dwivedi in Colloq Math 179(1):87–105, 2025, Problem 3.18). We also provide a local solution to this problem without any additional assumptions on the Banach space X. Motivated by the work of Daptari et al. (Rev R Acad Cienc Exactas Fís Nat Ser A Mat 119(3):82, 2025), we show that if the set of all \(\hbox {weak}^{*}\) weak -weak points of continuity of \(L^{1}(\mu , X)_{1}^{*}\) L 1 ( μ , X ) 1 is weakly dense in \(L^{1}(\mu , X)_{1}^{*}\) L 1 ( μ , X ) 1 , then \(X^{*}\) X has the Radon–Nikodým property (RNP) (see Theorem 3.12).