<p>Let <i>K</i> be a field equipped with a Henselian valuation, and let <i>D</i> be a tame central division algebra over the field <i>K</i>. Denote by <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{TK}_1(D)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>TK</mtext> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> the torsion subgroup of the Whitehead group <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="118" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{K}_1(D) = D^*/D'\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>K</mtext> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mi>D</mi> <mo>∗</mo> </msup> <mo stretchy="false">/</mo> <msup> <mi>D</mi> <mo>′</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq3.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(D^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>D</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation> is the multiplicative group of <i>D</i> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq4.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\(D'\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>D</mi> <mo>′</mo> </msup> </math></EquationSource> </InlineEquation> is its derived subgroup. Let <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq5.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textbf{G}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="bold">G</mi> </math></EquationSource> </InlineEquation> be the subgroup of <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq3.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(D^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>D</mi> <mo>∗</mo> </msup> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="123" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{TK}_1(D) = \textbf{G}/D'\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>TK</mtext> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi mathvariant="bold">G</mi> <mo stretchy="false">/</mo> <msup> <mi>D</mi> <mo>′</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>. In this note, we prove that either <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="145" /> </InlineMediaObject> <EquationSource Format="TEX">\((1 + M_D) \cap \textbf{G} \subseteq D'\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>M</mi> <mi>D</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>∩</mo> <mi mathvariant="bold">G</mi> <mo>⊆</mo> <msup> <mi>D</mi> <mo>′</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>, or the residue field <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq9.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(\overline{K}\)</EquationSource> <EquationSource Format="MATHML"><math> <mover> <mi>K</mi> <mo>¯</mo> </mover> </math></EquationSource> </InlineEquation> has characteristic <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq10.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(p &gt; 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation> and the group <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq11.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="201" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textbf{H}:= ((1 + M_D) \cap \textbf{G})D'/D'\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="bold">H</mi> <mo>:</mo> <mo>=</mo> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <msub> <mi>M</mi> <mi>D</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>∩</mo> <mi mathvariant="bold">G</mi> <mo stretchy="false">)</mo> </mrow> <msup> <mi>D</mi> <mo>′</mo> </msup> <mo stretchy="false">/</mo> <msup> <mi>D</mi> <mo>′</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> is a <i>p</i>-group. Additionally, we provide examples of valued division algebras with non-trivial <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq12.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textbf{H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="bold">H</mi> </math></EquationSource> </InlineEquation>. This illustrates that, in contrast to the reduced Whitehead group <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq13.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{SK}_1(D)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>SK</mtext> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, a complete analogue of the congruence theorem does not hold for <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2149_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{TK}_1(D)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>TK</mtext> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>.</p>

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On the congruence theorem for valued division algebras

  • Huynh Viet Khanh,
  • Nguyen Duc Anh Khoa

摘要

Let K be a field equipped with a Henselian valuation, and let D be a tame central division algebra over the field K. Denote by \(\textrm{TK}_1(D)\) TK 1 ( D ) the torsion subgroup of the Whitehead group \(\textrm{K}_1(D) = D^*/D'\) K 1 ( D ) = D / D , where \(D^*\) D is the multiplicative group of D and \(D'\) D is its derived subgroup. Let \(\textbf{G}\) G be the subgroup of \(D^*\) D such that \(\textrm{TK}_1(D) = \textbf{G}/D'\) TK 1 ( D ) = G / D . In this note, we prove that either \((1 + M_D) \cap \textbf{G} \subseteq D'\) ( 1 + M D ) G D , or the residue field \(\overline{K}\) K ¯ has characteristic \(p > 0\) p > 0 and the group \(\textbf{H}:= ((1 + M_D) \cap \textbf{G})D'/D'\) H : = ( ( 1 + M D ) G ) D / D is a p-group. Additionally, we provide examples of valued division algebras with non-trivial \(\textbf{H}\) H . This illustrates that, in contrast to the reduced Whitehead group \(\textrm{SK}_1(D)\) SK 1 ( D ) , a complete analogue of the congruence theorem does not hold for \(\textrm{TK}_1(D)\) TK 1 ( D ) .