<p>The question of whether the group <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2158_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="58" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {Q}}_p \rtimes {\mathbb {Q}}_p^*\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="double-struck">Q</mi> <mi>p</mi> </msub> <mo>⋊</mo> <msubsup> <mi mathvariant="double-struck">Q</mi> <mi>p</mi> <mo>∗</mo> </msubsup> </mrow> </math></EquationSource> </InlineEquation> is Hermitian has been stated as an open question in multiple sources in the literature, even as recently as a paper by R. Palma published in 2015. In this note, we confirm that this group is Hermitian by proving the following more general theorem: given any local field <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2158_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="12" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {K}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">K</mi> </math></EquationSource> </InlineEquation>, the affine group <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2158_Article_IEq3.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="51" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {K}} \rtimes {\mathbb {K}}^*\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">K</mi> <mo>⋊</mo> <msup> <mrow> <mi mathvariant="double-struck">K</mi> </mrow> <mo>∗</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> is a Hermitian group. The proof is a consequence of results about Hermitian Banach <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2158_Article_IEq4.gif" Format="GIF" Height="9" Rendition="HTML" Resolution="72" Type="Linedraw" Width="12" /> </InlineMediaObject> <EquationSource Format="TEX">\(*\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow /> <mo>∗</mo> </mrow> </math></EquationSource> </InlineEquation>-algebras from the 1970s. In the case that <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2158_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="12" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {K}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">K</mi> </math></EquationSource> </InlineEquation> is a non-archimedean local field, this result produces examples of totally disconnected locally compact Hermitian groups with exponential growth, and these are the first examples of groups satisfying these properties. This answers a second question of Palma about the existence of such groups.</p>

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The affine group of a local field is Hermitian

  • Max Carter

摘要

The question of whether the group \({\mathbb {Q}}_p \rtimes {\mathbb {Q}}_p^*\) Q p Q p is Hermitian has been stated as an open question in multiple sources in the literature, even as recently as a paper by R. Palma published in 2015. In this note, we confirm that this group is Hermitian by proving the following more general theorem: given any local field \({\mathbb {K}}\) K , the affine group \({\mathbb {K}} \rtimes {\mathbb {K}}^*\) K K is a Hermitian group. The proof is a consequence of results about Hermitian Banach \(*\) -algebras from the 1970s. In the case that \({\mathbb {K}}\) K is a non-archimedean local field, this result produces examples of totally disconnected locally compact Hermitian groups with exponential growth, and these are the first examples of groups satisfying these properties. This answers a second question of Palma about the existence of such groups.