<p>We show that if <i>G</i> is a finite group whose Sylow 2-subgroups are wreathed 2-groups <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(W \cong (C_{2^n} \times C_{2^n}) \rtimes C_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <mo>≅</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>C</mi> <msup> <mn>2</mn> <mi>n</mi> </msup> </msub> <mo>×</mo> <msub> <mi>C</mi> <msup> <mn>2</mn> <mi>n</mi> </msup> </msub> <mo stretchy="false">)</mo> </mrow> <mo>⋊</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(n \ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, then the intersection <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\operatorname {Out}_c(G) \cap \operatorname {Out}_{\textrm{Col}}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo>Out</mo> <mi>c</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>∩</mo> <msub> <mo>Out</mo> <mtext>Col</mtext> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> has odd order, where <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\operatorname {Out}_c(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo>Out</mo> <mi>c</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\operatorname {Out}_{\textrm{Col}}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo>Out</mo> <mtext>Col</mtext> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> denote the class-preserving and Coleman outer automorphism groups, respectively. In particular, <i>G</i> satisfies the normalizer condition for its integral group ring. Together with earlier results for the dihedral and semidihedral cases, this settles the question for all finite groups whose Sylow 2-subgroups are of 2-rank two. We recall that the finite simple groups with such Sylow 2-subgroups were classified by Gorenstein and Walter in the dihedral case (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\textrm{PSL}(2,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>PSL</mtext> <mo stretchy="false">(</mo> <mn>2</mn> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> with <i>q</i> odd, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(q \ge 5\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>q</mi> <mo>≥</mo> <mn>5</mn> </mrow> </math></EquationSource> </InlineEquation>, and the alternating group <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(A_7\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mn>7</mn> </msub> </math></EquationSource> </InlineEquation>) and by Alperin, Brauer, and Gorenstein in the semidihedral and wreathed cases (the groups <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\textrm{PSL}(3,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>PSL</mtext> <mo stretchy="false">(</mo> <mn>3</mn> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\textrm{PSU}(3,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>PSU</mtext> <mo stretchy="false">(</mo> <mn>3</mn> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> for suitable odd&#xa0;<i>q</i>, with the Mathieu group <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(M_{11}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>M</mi> <mn>11</mn> </msub> </math></EquationSource> </InlineEquation> appearing in the semidihedral case only).</p>

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Class-preserving Coleman automorphisms of finite groups with Wreathed Sylow 2-subgroups

  • Riccardo Aragona

摘要

We show that if G is a finite group whose Sylow 2-subgroups are wreathed 2-groups \(W \cong (C_{2^n} \times C_{2^n}) \rtimes C_2\) W ( C 2 n × C 2 n ) C 2 with \(n \ge 2\) n 2 , then the intersection \(\operatorname {Out}_c(G) \cap \operatorname {Out}_{\textrm{Col}}(G)\) Out c ( G ) Out Col ( G ) has odd order, where \(\operatorname {Out}_c(G)\) Out c ( G ) and \(\operatorname {Out}_{\textrm{Col}}(G)\) Out Col ( G ) denote the class-preserving and Coleman outer automorphism groups, respectively. In particular, G satisfies the normalizer condition for its integral group ring. Together with earlier results for the dihedral and semidihedral cases, this settles the question for all finite groups whose Sylow 2-subgroups are of 2-rank two. We recall that the finite simple groups with such Sylow 2-subgroups were classified by Gorenstein and Walter in the dihedral case ( \(\textrm{PSL}(2,q)\) PSL ( 2 , q ) with q odd, \(q \ge 5\) q 5 , and the alternating group \(A_7\) A 7 ) and by Alperin, Brauer, and Gorenstein in the semidihedral and wreathed cases (the groups \(\textrm{PSL}(3,q)\) PSL ( 3 , q ) and \(\textrm{PSU}(3,q)\) PSU ( 3 , q ) for suitable odd q, with the Mathieu group \(M_{11}\) M 11 appearing in the semidihedral case only).