<p>Let <i>p</i> be an odd prime and <i>P</i> a Sylow <i>p</i>-subgroup of a finite group <i>G</i>. If <i>P</i> is either metacyclic or each of its elements of order <i>p</i> lies in the center, then <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\(N_G(P)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mi>G</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>P</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> controls strong <i>G</i>-fusion in <i>P</i>, as established in Martino and Priddy (Math. Z. 225(2):277–288, 1997, Theorems 2.7 and 4.1). First, we provide alternative proofs for these results without relying on the Alperin fusion theorem, thereby simplifying the theoretical framework. Second, we establish an equivalence for the control of fusion in terms of a permutation character. Specifically, we define the permutation character induced by the action of <i>G</i> on <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq2.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(Syl_p(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>S</mi> <mi>y</mi> <msub> <mi>l</mi> <mi>p</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> as <i>the Sylow </i><i>p</i><i>-character of</i> <i>G</i>. Now let <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq3.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="93" /> </InlineMediaObject> <EquationSource Format="TEX">\(P\in Syl_p(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>P</mi> <mo>∈</mo> <mi>S</mi> <mi>y</mi> <msub> <mi>l</mi> <mi>p</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="128" /> </InlineMediaObject> <EquationSource Format="TEX">\(N_G(P)\le N \le G \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mi>G</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>P</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mi>N</mi> <mo>≤</mo> <mi>G</mi> </mrow> </math></EquationSource> </InlineEquation>. Set <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq5.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="35" /> </InlineMediaObject> <EquationSource Format="TEX">\(\chi ,\psi \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>,</mo> <mi>ψ</mi> </mrow> </math></EquationSource> </InlineEquation> to be the Sylow <i>p</i>-characters of <i>G</i> and <i>N</i>, respectively. Then we prove that <i>N</i> controls <i>G</i>-fusion in <i>P</i> if and only if <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13_2025_2101_Article_IEq6.gif" Format="GIF" Height="28" Rendition="HTML" Resolution="72" Type="Linedraw" Width="190" /> </InlineMediaObject> <EquationSource Format="TEX">\(\frac{\chi (g)}{\psi (g)}=\frac{|C_G(g)|}{|C_N(g)|} \text { for all } g\in P.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mfrac> <mrow> <mi>χ</mi> <mo stretchy="false">(</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mi>ψ</mi> <mo stretchy="false">(</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mrow> <mo stretchy="false">|</mo> </mrow> <msub> <mi>C</mi> <mi>G</mi> </msub> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> </mrow> <mrow> <mrow> <mo stretchy="false">|</mo> </mrow> <msub> <mi>C</mi> <mi>N</mi> </msub> <mrow> <mrow> <mo stretchy="false">(</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> </mrow> </mfrac> <mspace width="0.333333em" /> <mtext>for all</mtext> <mspace width="0.333333em" /> <mi>g</mi> <mo>∈</mo> <mi>P</mi> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> In the case that <i>N</i> is a <i>p</i>-local subgroup, further results are obtained.</p>

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A geodesic insight into some fundamental fusion theorems

  • M. Yasir Kızmaz

摘要

Let p be an odd prime and P a Sylow p-subgroup of a finite group G. If P is either metacyclic or each of its elements of order p lies in the center, then \(N_G(P)\) N G ( P ) controls strong G-fusion in P, as established in Martino and Priddy (Math. Z. 225(2):277–288, 1997, Theorems 2.7 and 4.1). First, we provide alternative proofs for these results without relying on the Alperin fusion theorem, thereby simplifying the theoretical framework. Second, we establish an equivalence for the control of fusion in terms of a permutation character. Specifically, we define the permutation character induced by the action of G on \(Syl_p(G)\) S y l p ( G ) as the Sylow p-character of G. Now let \(P\in Syl_p(G)\) P S y l p ( G ) , and \(N_G(P)\le N \le G \) N G ( P ) N G . Set \(\chi ,\psi \) χ , ψ to be the Sylow p-characters of G and N, respectively. Then we prove that N controls G-fusion in P if and only if \(\frac{\chi (g)}{\psi (g)}=\frac{|C_G(g)|}{|C_N(g)|} \text { for all } g\in P.\) χ ( g ) ψ ( g ) = | C G ( g ) | | C N ( g ) | for all g P . In the case that N is a p-local subgroup, further results are obtained.