<p>An algebra is bicommutative if it satisfies left and right symmetries; i.e., <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(a(bc)=b(ac)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mo stretchy="false">(</mo> <mi>b</mi> <mi>c</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mi>b</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mi>c</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\((ab)c=(ac)b\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>a</mi> <mi>b</mi> <mo stretchy="false">)</mo> <mi>c</mi> <mo>=</mo> <mo stretchy="false">(</mo> <mi>a</mi> <mi>c</mi> <mo stretchy="false">)</mo> <mi>b</mi> </mrow> </math></EquationSource> </InlineEquation>. Let <i>K</i> be a field of characteristic zero, and <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(M_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>M</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(n\ge 3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>3</mn> </mrow> </math></EquationSource> </InlineEquation>, be the free metabelian bicommutative algebra generated by a set <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(X_n=\{x_1,\ldots ,x_n\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>X</mi> <mi>n</mi> </msub> <mo>=</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>x</mi> <mi>n</mi> </msub> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of variables, in which the identity <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\((xy)(zt)=0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mi>y</mi> <mo stretchy="false">)</mo> <mo stretchy="false">(</mo> <mi>z</mi> <mi>t</mi> <mo stretchy="false">)</mo> <mo>=</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation> is being satisfied. We define the action of the alternating group <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(A_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> on <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(M_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>M</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> as follows. <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\pi f(x_1,\ldots ,x_n)=f(x_{\pi (1)},\ldots ,x_{\pi (n)})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>π</mi> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>x</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>x</mi> <mrow> <mi>π</mi> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>x</mi> <mrow> <mi>π</mi> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\pi \in A_n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>π</mi> <mo>∈</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(f\in M_n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>∈</mo> <msub> <mi>M</mi> <mi>n</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>. The set <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(M_n^{A_n}=\{f\in M_n\mid \pi f=f\ , \forall \pi \in A_n\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>M</mi> <mi>n</mi> <msub> <mi>A</mi> <mi>n</mi> </msub> </msubsup> <mo>=</mo> <mrow> <mo stretchy="false">{</mo> <mi>f</mi> <mo>∈</mo> <msub> <mi>M</mi> <mi>n</mi> </msub> <mo>∣</mo> <mi>π</mi> <mi>f</mi> <mo>=</mo> <mi>f</mi> <mspace width="4pt" /> <mo>,</mo> <mo>∀</mo> <mi>π</mi> <mo>∈</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is a subalgebra of <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(M_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>M</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> called the algebra of invariants of the group <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(A_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>A</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>. In the first part of this study, we describe the elements of the algebra <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(M_n^{A_n}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>M</mi> <mi>n</mi> <msub> <mi>A</mi> <mi>n</mi> </msub> </msubsup> </math></EquationSource> </InlineEquation>. We also give the description of the algebras <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(M_2^{C_2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>M</mi> <mn>2</mn> <msub> <mi>C</mi> <mn>2</mn> </msub> </msubsup> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\(M_2^{C_3}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>M</mi> <mn>2</mn> <msub> <mi>C</mi> <mn>3</mn> </msub> </msubsup> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(M_2^{C_2\times C_2}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>M</mi> <mn>2</mn> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>×</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> </mrow> </msubsup> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\(M_2^{C_4}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>M</mi> <mn>2</mn> <msub> <mi>C</mi> <mn>4</mn> </msub> </msubsup> </math></EquationSource> </InlineEquation> of invariants of the groups <InlineEquation ID="IEq20"> <EquationSource Format="TEX">\(C_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>C</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq21"> <EquationSource Format="TEX">\(C_3\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>C</mi> <mn>3</mn> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq22"> <EquationSource Format="TEX">\(C_2\times C_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>×</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq23"> <EquationSource Format="TEX">\(C_4\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>C</mi> <mn>4</mn> </msub> </math></EquationSource> </InlineEquation> of order up to 4, respectively, as a subgroups of the general linear group <InlineEquation ID="IEq24"> <EquationSource Format="TEX">\(\text {GL}_2(K)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mtext>GL</mtext> <mn>2</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>K</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>.</p>

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On invariants of free metabelian bicommutative algebras

  • Nazar Şahin Öğüşlü,
  • Şehmus Fındık

摘要

An algebra is bicommutative if it satisfies left and right symmetries; i.e., \(a(bc)=b(ac)\) a ( b c ) = b ( a c ) and \((ab)c=(ac)b\) ( a b ) c = ( a c ) b . Let K be a field of characteristic zero, and \(M_n\) M n , \(n\ge 3\) n 3 , be the free metabelian bicommutative algebra generated by a set \(X_n=\{x_1,\ldots ,x_n\}\) X n = { x 1 , , x n } of variables, in which the identity \((xy)(zt)=0\) ( x y ) ( z t ) = 0 is being satisfied. We define the action of the alternating group \(A_n\) A n on \(M_n\) M n as follows. \(\pi f(x_1,\ldots ,x_n)=f(x_{\pi (1)},\ldots ,x_{\pi (n)})\) π f ( x 1 , , x n ) = f ( x π ( 1 ) , , x π ( n ) ) , where \(\pi \in A_n\) π A n and \(f\in M_n\) f M n . The set \(M_n^{A_n}=\{f\in M_n\mid \pi f=f\ , \forall \pi \in A_n\}\) M n A n = { f M n π f = f , π A n } is a subalgebra of \(M_n\) M n called the algebra of invariants of the group \(A_n\) A n . In the first part of this study, we describe the elements of the algebra \(M_n^{A_n}\) M n A n . We also give the description of the algebras \(M_2^{C_2}\) M 2 C 2 , \(M_2^{C_3}\) M 2 C 3 , \(M_2^{C_2\times C_2}\) M 2 C 2 × C 2 , and \(M_2^{C_4}\) M 2 C 4 of invariants of the groups \(C_2\) C 2 , \(C_3\) C 3 , \(C_2\times C_2\) C 2 × C 2 , and \(C_4\) C 4 of order up to 4, respectively, as a subgroups of the general linear group \(\text {GL}_2(K)\) GL 2 ( K ) .