<p>We are interested in computing the Bredon cohomology with coefficients in the constant Mackey functor <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\underline{{\mathbb {F}}_2}\)</EquationSource> <EquationSource Format="MATHML"><math> <munder> <msub> <mi mathvariant="double-struck">F</mi> <mn>2</mn> </msub> <mo>̲</mo> </munder> </math></EquationSource> </InlineEquation> for equivariant <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="60" /> </InlineMediaObject> <EquationSource Format="TEX">\(\text {Rep}(C_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Rep</mtext> <mo stretchy="false">(</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> spaces, in particular for Grassmannian manifolds of the form <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {Gr}_k(V)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo>Gr</mo> <mi>k</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>V</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> where <i>V</i> is some real representation of <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="25" /> </InlineMediaObject> <EquationSource Format="TEX">\(C_2.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> It is possible to create multiple distinct <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="60" /> </InlineMediaObject> <EquationSource Format="TEX">\(\text {Rep}(C_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>Rep</mtext> <mo stretchy="false">(</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> constructions of (and hence multiple filtration spectral sequences for) a given Grassmannian. For sufficiently small examples one may exhaustively compute all possible outcomes of each spectral sequence and determine if there exists a unique common answer. However, the complexity of such a computation quickly balloons in time and memory requirements. We introduce a statistic on <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {M}_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">M</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>-modules valued in the polynomial ring <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="47" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb Z[x,y]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="double-struck">Z</mi> <mo stretchy="false">[</mo> <mi>x</mi> <mo>,</mo> <mi>y</mi> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> which makes cohomology computation of Rep<InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40062_2025_375_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">\((C_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-complexes more tractable, and we present some new results for Grassmannians.</p>

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Bigraded Poincaré polynomials and the equivariant cohomology of Rep\((C_2)\)-complexes

  • Eric Hogle

摘要

We are interested in computing the Bredon cohomology with coefficients in the constant Mackey functor \(\underline{{\mathbb {F}}_2}\) F 2 ̲ for equivariant \(\text {Rep}(C_2)\) Rep ( C 2 ) spaces, in particular for Grassmannian manifolds of the form \(\operatorname {Gr}_k(V)\) Gr k ( V ) where V is some real representation of \(C_2.\) C 2 . It is possible to create multiple distinct \(\text {Rep}(C_2)\) Rep ( C 2 ) constructions of (and hence multiple filtration spectral sequences for) a given Grassmannian. For sufficiently small examples one may exhaustively compute all possible outcomes of each spectral sequence and determine if there exists a unique common answer. However, the complexity of such a computation quickly balloons in time and memory requirements. We introduce a statistic on \(\mathbb {M}_2\) M 2 -modules valued in the polynomial ring \(\mathbb Z[x,y]\) Z [ x , y ] which makes cohomology computation of Rep \((C_2)\) ( C 2 ) -complexes more tractable, and we present some new results for Grassmannians.