<p>A well-known theorem of Bochner, generalized by Eberlein, characterizes the image of Fourier-Stieltjes transform of the measure algebra of a locally compact abelian group. With the approach that arose from this theorem, the concept of BSE-Algebras was created by Takahasi and Hatori to study the Gelfand image of commutative Banach algebras. Let <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {A}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">A</mi> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {B}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">B</mi> </math></EquationSource> </InlineEquation> be two semisimple commutative Banach algebras. We denote by <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathfrak {A}{\tilde{\otimes }}\mathfrak {B}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">A</mi> <mover accent="true"> <mo>⊗</mo> <mo stretchy="false">~</mo> </mover> <mi mathvariant="fraktur">B</mi> </mrow> </math></EquationSource> </InlineEquation> a Banach algebra obtained by the completion of <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq4.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathfrak {A}\otimes \mathfrak {B}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">A</mi> <mo>⊗</mo> <mi mathvariant="fraktur">B</mi> </mrow> </math></EquationSource> </InlineEquation> w.r.t. a submultiplicative cross-norm which dominates the injective norm. In this article, we provide necessary and sufficient conditions for <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathfrak {A}{\tilde{\otimes }}\mathfrak {B}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">A</mi> <mover accent="true"> <mo>⊗</mo> <mo stretchy="false">~</mo> </mover> <mi mathvariant="fraktur">B</mi> </mrow> </math></EquationSource> </InlineEquation> to be a BSE-algebra. We give an extension of Bochner-Eberlein theorem. We also provide another proof for the well-known fact that the injective tensor product of <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {A}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">A</mi> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {B}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">B</mi> </math></EquationSource> </InlineEquation> is isomorphic to a <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq8.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(C^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>C</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation>-algebra if and only if <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {A}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">A</mi> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {B}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">B</mi> </math></EquationSource> </InlineEquation> are so. For a discrete space <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq11.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="13" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Ω</mi> </math></EquationSource> </InlineEquation>, it is proved that the space <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq12.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="61" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathcal {C}}_0(\Omega ,{\mathfrak {A}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="script">C</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Ω</mi> <mo>,</mo> <mi mathvariant="fraktur">A</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>,&#xa0;the set of all continuous functions <InlineEquation ID="IEq2000"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq2000.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="TEX">\(f:\Omega\rightarrow\mathfrak A\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>:</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">→</mo> <mi mathvariant="fraktur">A</mi> </mrow> </math></EquationSource> </InlineEquation> that vanish at infinity, is a BSE-algebra if and only if <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41478_2025_887_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathfrak {A}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">A</mi> </math></EquationSource> </InlineEquation> is a BSE-algebra.</p>

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On characterizations of the image of the Gelfand transform of some Banach algebras of vector-valued functions

  • Meisam Soleimani Malekan

摘要

A well-known theorem of Bochner, generalized by Eberlein, characterizes the image of Fourier-Stieltjes transform of the measure algebra of a locally compact abelian group. With the approach that arose from this theorem, the concept of BSE-Algebras was created by Takahasi and Hatori to study the Gelfand image of commutative Banach algebras. Let \({\mathfrak {A}}\) A and \({\mathfrak {B}}\) B be two semisimple commutative Banach algebras. We denote by \(\mathfrak {A}{\tilde{\otimes }}\mathfrak {B}\) A ~ B a Banach algebra obtained by the completion of \(\mathfrak {A}\otimes \mathfrak {B}\) A B w.r.t. a submultiplicative cross-norm which dominates the injective norm. In this article, we provide necessary and sufficient conditions for \(\mathfrak {A}{\tilde{\otimes }}\mathfrak {B}\) A ~ B to be a BSE-algebra. We give an extension of Bochner-Eberlein theorem. We also provide another proof for the well-known fact that the injective tensor product of \({\mathfrak {A}}\) A and \({\mathfrak {B}}\) B is isomorphic to a \(C^*\) C -algebra if and only if \({\mathfrak {A}}\) A and \({\mathfrak {B}}\) B are so. For a discrete space \(\Omega\) Ω , it is proved that the space \({\mathcal {C}}_0(\Omega ,{\mathfrak {A}})\) C 0 ( Ω , A ) , the set of all continuous functions \(f:\Omega\rightarrow\mathfrak A\) f : Ω A that vanish at infinity, is a BSE-algebra if and only if \({\mathfrak {A}}\) A is a BSE-algebra.