<p>Let <i>X</i> be a smooth hypersurface of degree <i>d</i> in the projective space <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="34" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {P}}^{n+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">P</mi> </mrow> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> </math></EquationSource> </InlineEquation>, and <i>G</i> be an abelian group subgroup of the automorphism group of <i>X</i> where <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq2.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(n\ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="41" /> </InlineMediaObject> <EquationSource Format="TEX">\(d\ge 3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo>≥</mo> <mn>3</mn> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="98" /> </InlineMediaObject> <EquationSource Format="TEX">\((n,d)\not =(2,4)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>d</mi> <mo stretchy="false">)</mo> <mo>≠</mo> <mo stretchy="false">(</mo> <mn>2</mn> <mo>,</mo> <mn>4</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. In this paper, we determine the group structure of <i>G</i> such that the quotient space <i>X</i>/<i>G</i> is smooth. In addition, we show that if <i>X</i>/<i>G</i> is isomorphic to <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq5.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {P}}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">P</mi> </mrow> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation>, then <i>X</i> has an outer Galois point <i>p</i>, and the quotient morphism <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13366_2024_775_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="105" /> </InlineMediaObject> <EquationSource Format="TEX">\(q:X\rightarrow X/G\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>q</mi> <mo>:</mo> <mi>X</mi> <mo stretchy="false">→</mo> <mi>X</mi> <mo stretchy="false">/</mo> <mi>G</mi> </mrow> </math></EquationSource> </InlineEquation> factors through a projection at an outer Galois point <i>p</i>.</p>

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Abelian automorphism groups of smooth hypersurfaces with smooth quotient

  • Taro Hayashi

摘要

Let X be a smooth hypersurface of degree d in the projective space \({\mathbb {P}}^{n+1}\) P n + 1 , and G be an abelian group subgroup of the automorphism group of X where \(n\ge 2\) n 2 , \(d\ge 3\) d 3 , and \((n,d)\not =(2,4)\) ( n , d ) ( 2 , 4 ) . In this paper, we determine the group structure of G such that the quotient space X/G is smooth. In addition, we show that if X/G is isomorphic to \({\mathbb {P}}^n\) P n , then X has an outer Galois point p, and the quotient morphism \(q:X\rightarrow X/G\) q : X X / G factors through a projection at an outer Galois point p.