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arXiv 2512.20187math.RA
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一个生成元代数

One generator algebras

Mohamad Maassarani

AI总结:

本文研究了由一个元素生成的完美域上代数的结构,证明其自同构群的分解形式及特定代数的同构分类。

摘要:

对于一个非同构的环族 $R_1,R_2,R_3,\dots$,每个环(或代数)只有两个幂等元(1和0),我们对通过不同 $R_i$ 的幂的乘积得到的环(或代数)进行分类。我们证明此类环(或代数)的自同构群自然地分解为 wreath 乘积的乘积 $Aut( R_n)\wr \mathfrak{S}_{m_n} $。这些结果应用于完美域 $\mathbb{K}$ 上由一个元素生成的代数。此类代数要么是 $\mathbb{K}[X]$,要么是 $\mathbb{K}[X]$ 的商代数。我们证明在后一种情况下,该代数同构于有限乘积的形式 $A=\prod (\mathbb{L}_i[X]/(X^j))^{n_{i,j}}$,其中 $\mathbb{L}_i$ 是非同构的有限域扩张(不作为 $\mathbb{K}$-代数同构),当 $\mathbb{K}$ 有限时,对 $n_{i,j}$ 有限制。我们对这些代数进行同构分类。我们还证明 $\mathbb{K}$-代数 $A=\prod (\mathbb{L}_i[X]/(X^j))^{n_{i,j}}$ 的自同构群自然地分解为 wreath 乘积的乘积 $Aut_\mathbb{K}(\mathbb{L}_i[X]/(X^j) )\wr \mathfrak{S}_{n_{i,j}}$($Aut_\mathbb{K}(-)$ 表示 $\mathbb{K}$-代数自同构群)。最后,我们证明 $Aut_\mathbb{K}(\mathbb{L}_i[X]/(X^n) )$ 与半直积 $G_n(\mathbb{L}_i)\rtimes Aut_\mathbb{K}(\mathbb{L}_i)$($Aut_\mathbb{K}(-)$ 表示 $\mathbb{K}$-代数自同构群)同构,其中 $G_n(\mathbb{L}_i)\simeq Aut_{\mathbb{L}_i}(\mathbb{L}_i[X]/(X^n) )$($\mathbb{L}_i$ 代数自同构群)是一个由系数在 $\mathbb{L}_i}$ 中的可逆下三角矩阵组成的代数子群,尺寸为 $(n-1)\times (n-1)$;矩阵 $M\in G_n(\mathbb{L}_i)$ 在 $σ\in Aut_\mathbb{K}(\mathbb{L}_i)$ 下的共轭是通过将 $M$ 的系数应用 $σ$ 得到的矩阵。

英文摘要:

For $R_1,R_2,R_3,\dots$ a family of non isomorphic rings (or algebras) having each only 2 idempotents ($1$ and $0$), we classify up to isomorphism the rings (or algebras) obtained by taking products of powers of the different $R_i$. We show that the automorphism groups of such rings (or algebras) split naturally into the product of wreath products $Aut( R_n)\wr \mathfrak{S}_{m_n} $ for different $n$. These results are applied to algebras generated by one element over a perfect field $\mathbb{K}$. Such algebra is either $\mathbb{K}[X]$ or a quotient of $\mathbb{K}[X]$. We show that in the later case the algebra is isomorphic to a finite product of the form $A=\prod (\mathbb{L}_i[X]/(X^j))^{n_{i,j}}$, where the $\mathbb{L}_i$ are non isomomorphic finite field extensions of $\mathbb{K}$ $($not isomophic as $\mathbb{K}$-algebras$)$, with restrictions on the numbers $n_{i,j}$ if $\mathbb{K}$ is finite. We classify these algebras up to isomorphism. We have also that the $\mathbb{K}$-algebra automorphism group of $A=\prod (\mathbb{L}_i[X]/(X^j))^{n_{i,j}}$ splits naturally into the product of wreat products $Aut_\mathbb{K}(\mathbb{L}_i[X]/(X^j) )\wr \mathfrak{S}_{n_{i,j}}$ ($Aut_\mathbb{K}(-)$ is for $\mathbb{K}$-algebra automorphism group). Finally, we prove that $Aut_\mathbb{K}(\mathbb{L}_i[X]/(X^n) )$ is isomorphic to the semi-direct product $G_n(\mathbb{L}_i)\rtimes Aut_\mathbb{K}(\mathbb{L}_i)$ ($Aut_\mathbb{K}(-)$ is for $\mathbb{K}$-algebra automorphism group), where $G_n(\mathbb{L}_i)\simeq Aut_{\mathbb{L}_i}(\mathbb{L}_i[X]/(X^n) )$ ($\mathbb{L}_i$ algebra automorphism group) is an algebraic subgroup of invertible lower triangular matrices of dimension $(n-1)\times (n-1)$ with coefficients in $\mathbb{L}_i$; the conjugate of a matrix $M\in G_n(\mathbb{L}_i)$ by $σ\in Aut_\mathbb{K}(\mathbb{L}_i)$ is the matrix obtained from $M$ by applying $σ$ to its coefficients.

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