<p>Let <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(S_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>S</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> denote the symmetric group. We consider <Equation ID="Equ6"> <EquationSource Format="TEX">\(\begin{aligned} N_{\ell }(n):= \frac{\left| \textrm{Hom}\left( {\mathbb {Z}}^{\ell },S_n\right) \right| }{n!} \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi>N</mi> <mi>ℓ</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mfrac> <mfenced close="|" open="|"> <mtext>Hom</mtext> <mfenced close=")" open="("> <msup> <mrow> <mi mathvariant="double-struck">Z</mi> </mrow> <mi>ℓ</mi> </msup> <mo>,</mo> <msub> <mi>S</mi> <mi>n</mi> </msub> </mfenced> </mfenced> <mrow> <mi>n</mi> <mo>!</mo> </mrow> </mfrac> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>which also counts the number of <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\ell \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ℓ</mi> </math></EquationSource> </InlineEquation>-tuples <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\pi =\left( \pi _1, \ldots , \pi _{\ell }\right) \in S_n^{\ell }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>π</mi> <mo>=</mo> <mfenced close=")" open="("> <msub> <mi>π</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>π</mi> <mi>ℓ</mi> </msub> </mfenced> <mo>∈</mo> <msubsup> <mi>S</mi> <mi>n</mi> <mi>ℓ</mi> </msubsup> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\pi _i \pi _j = \pi _j \pi _i\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>π</mi> <mi>i</mi> </msub> <msub> <mi>π</mi> <mi>j</mi> </msub> <mo>=</mo> <msub> <mi>π</mi> <mi>j</mi> </msub> <msub> <mi>π</mi> <mi>i</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(1 \le i,j \le \ell \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>i</mi> <mo>,</mo> <mi>j</mi> <mo>≤</mo> <mi>ℓ</mi> </mrow> </math></EquationSource> </InlineEquation> scaled by <i>n</i>!. A recursion formula, generating function, and Euler product have been discovered by Dey, Wohlfahrt, Bryan and Fulman, and White. Let <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(a,b, \ell \ge 2.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo>,</mo> <mi>b</mi> <mo>,</mo> <mi>ℓ</mi> <mo>≥</mo> <mn>2</mn> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> It is known by Bringmann, Franke, and Heim, that the Bessenrodt–Ono inequality <Equation ID="Equ7"> <EquationSource Format="TEX">\(\begin{aligned} \Delta _{a,b}^{\ell }:= N_{\ell }(a) \, N_{\ell }(b) - N_{\ell }(a+b) &gt;0 \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msubsup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>a</mi> <mo>,</mo> <mi>b</mi> </mrow> <mi>ℓ</mi> </msubsup> <mo>:</mo> <mo>=</mo> <msub> <mi>N</mi> <mi>ℓ</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> <mspace width="0.166667em" /> <msub> <mi>N</mi> <mi>ℓ</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>b</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <msub> <mi>N</mi> <mi>ℓ</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>a</mi> <mo>+</mo> <mi>b</mi> <mo stretchy="false">)</mo> </mrow> <mo>&gt;</mo> <mn>0</mn> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>is valid for <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(a,b \gg 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo>,</mo> <mi>b</mi> <mo>≫</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> and by Bessenrodt and Ono that it is valid for <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\ell =2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ℓ</mi> <mo>=</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(a+b &gt;9.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo>+</mo> <mi>b</mi> <mo>&gt;</mo> <mn>9</mn> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation> In this paper, we prove that for each pair (<i>a</i>,&#xa0;<i>b</i>) the sign of <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(\{\Delta _{a,b}^{\ell } \}_{\ell }\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msubsup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>a</mi> <mo>,</mo> <mi>b</mi> </mrow> <mi>ℓ</mi> </msubsup> <mo stretchy="false">}</mo> </mrow> <mi>ℓ</mi> </msub> </math></EquationSource> </InlineEquation> is getting stable. In each case we provide an explicit bound. The numbers <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(N_{\ell }\left( n\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mi>ℓ</mi> </msub> <mfenced close=")" open="("> <mi>n</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> had been identified by Bryan and Fulman as the <i>n</i>th orbifold characteristics, generalizing work by Macdonald and Hirzebruch–Höfer concerning the ordinary and string-theoretic Euler characteristics of symmetric products, where <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(N_2(n)=p(n) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>N</mi> <mn>2</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>p</mi> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> represents the partition function.</p>

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Bessenrodt–Ono Inequalities for \(\ell \)-Tuples of Pairwise Commuting Permutations

  • Abdelmalek Abdesselam,
  • Bernhard Heim,
  • Markus Neuhauser

摘要

Let \(S_n\) S n denote the symmetric group. We consider \(\begin{aligned} N_{\ell }(n):= \frac{\left| \textrm{Hom}\left( {\mathbb {Z}}^{\ell },S_n\right) \right| }{n!} \end{aligned}\) N ( n ) : = Hom Z , S n n ! which also counts the number of \(\ell \) -tuples \(\pi =\left( \pi _1, \ldots , \pi _{\ell }\right) \in S_n^{\ell }\) π = π 1 , , π S n with \(\pi _i \pi _j = \pi _j \pi _i\) π i π j = π j π i for \(1 \le i,j \le \ell \) 1 i , j scaled by n!. A recursion formula, generating function, and Euler product have been discovered by Dey, Wohlfahrt, Bryan and Fulman, and White. Let \(a,b, \ell \ge 2.\) a , b , 2 . It is known by Bringmann, Franke, and Heim, that the Bessenrodt–Ono inequality \(\begin{aligned} \Delta _{a,b}^{\ell }:= N_{\ell }(a) \, N_{\ell }(b) - N_{\ell }(a+b) >0 \end{aligned}\) Δ a , b : = N ( a ) N ( b ) - N ( a + b ) > 0 is valid for \(a,b \gg 1\) a , b 1 and by Bessenrodt and Ono that it is valid for \(\ell =2\) = 2 and \(a+b >9.\) a + b > 9 . In this paper, we prove that for each pair (ab) the sign of \(\{\Delta _{a,b}^{\ell } \}_{\ell }\) { Δ a , b } is getting stable. In each case we provide an explicit bound. The numbers \(N_{\ell }\left( n\right) \) N n had been identified by Bryan and Fulman as the nth orbifold characteristics, generalizing work by Macdonald and Hirzebruch–Höfer concerning the ordinary and string-theoretic Euler characteristics of symmetric products, where \(N_2(n)=p(n) \) N 2 ( n ) = p ( n ) represents the partition function.