<p>We investigate when the filtration induced by Beilinson’s spectral sequence splits non-canonically into a direct sum decomposition. We conclude that for any vector bundle <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2024_1605_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\mathcal {E}}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">E</mi> </math></EquationSource> </InlineEquation> on a projective space over an algebraically closed field of characteristic <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2024_1605_Article_IEq2.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> there exists <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2024_1605_Article_IEq3.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(r_{0}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>r</mi> <mn>0</mn> </msub> </math></EquationSource> </InlineEquation> such that for <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2024_1605_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="46" /> </InlineMediaObject> <EquationSource Format="TEX">\(r\ge r_{0}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo>≥</mo> <msub> <mi>r</mi> <mn>0</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> the Frobenius pushforward <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="229_2024_1605_Article_IEq5.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="29" /> </InlineMediaObject> <EquationSource Format="TEX">\({\textsf{F}^{r}_{*}}{{\mathcal {E}}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mmultiscripts> <mi mathvariant="sans-serif">F</mi> <mrow> <mrow /> <mo>∗</mo> </mrow> <mi>r</mi> </mmultiscripts> <mi mathvariant="script">E</mi> </mrow> </math></EquationSource> </InlineEquation> decomposes as a direct sum of line bundles and exterior powers of the cotangent bundle (we also give a variant for the "toric Frobenius map" valid in any characteristic). As an application we give a short proof of Klyachko’s theorem for vanishing of the cohomology of toric vector bundles on projective spaces.</p>

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Frobenius pushforwards of vector bundles on projective spaces

  • Feliks Rączka

摘要

We investigate when the filtration induced by Beilinson’s spectral sequence splits non-canonically into a direct sum decomposition. We conclude that for any vector bundle \({{\mathcal {E}}}\) E on a projective space over an algebraically closed field of characteristic \(p>0\) p > 0 there exists \(r_{0}\) r 0 such that for \(r\ge r_{0}\) r r 0 the Frobenius pushforward \({\textsf{F}^{r}_{*}}{{\mathcal {E}}}\) F r E decomposes as a direct sum of line bundles and exterior powers of the cotangent bundle (we also give a variant for the "toric Frobenius map" valid in any characteristic). As an application we give a short proof of Klyachko’s theorem for vanishing of the cohomology of toric vector bundles on projective spaces.