<p>We construct countable groups <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>G</mi> </math></EquationSource> <EquationSource Format="TEX">$G$</EquationSource> </InlineEquation> with the following new degree of <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq3.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="26" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msup> <mi mathvariant="normal">W</mi> <mo>∗</mo> </msup> </math></EquationSource> <EquationSource Format="TEX">$\mathrm{W}^{*}$</EquationSource> </InlineEquation>-superrigidity: if <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="39" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>L</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$L(G)$</EquationSource> </InlineEquation> is virtually isomorphic, in the sense of admitting a bifinite bimodule, with any other group von Neumann algebra <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="36" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>L</mi> <mo stretchy="false">(</mo> <mi mathvariant="normal">Λ</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$L(\Lambda )$</EquationSource> </InlineEquation>, then the groups <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq6.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>G</mi> </math></EquationSource> <EquationSource Format="TEX">$G$</EquationSource> </InlineEquation> and <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq7.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="13" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Λ</mi> </math></EquationSource> <EquationSource Format="TEX">$\Lambda $</EquationSource> </InlineEquation> must be virtually isomorphic. Moreover, we allow both group von Neumann algebras to be twisted by an arbitrary 2-cocycle. We also give examples of <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">II</mi> <mn>1</mn> </msub> </math></EquationSource> <EquationSource Format="TEX">$\mathrm{II}_{1}$</EquationSource> </InlineEquation> factors <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="222_2025_1320_Article_IEq9.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>N</mi> </math></EquationSource> <EquationSource Format="TEX">$N$</EquationSource> </InlineEquation> that are indecomposable in every sense: they are not virtually isomorphic to any cocycle twisted groupoid von Neumann algebra.</p>

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\(\mathrm{W}^{*}\)-Superrigidity for cocycle twisted group von Neumann algebras

  • Milan Donvil,
  • Stefaan Vaes

摘要

We construct countable groups G $G$ with the following new degree of W $\mathrm{W}^{*}$ -superrigidity: if L ( G ) $L(G)$ is virtually isomorphic, in the sense of admitting a bifinite bimodule, with any other group von Neumann algebra L ( Λ ) $L(\Lambda )$ , then the groups G $G$ and Λ $\Lambda $ must be virtually isomorphic. Moreover, we allow both group von Neumann algebras to be twisted by an arbitrary 2-cocycle. We also give examples of II 1 $\mathrm{II}_{1}$ factors N $N$ that are indecomposable in every sense: they are not virtually isomorphic to any cocycle twisted groupoid von Neumann algebra.