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arXiv 2209.03020math.AC
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参数理想幂紧闭包滤子的相伴分次环

Associated graded rings of the filtration of tight closure of powers of parameter ideals

Saipriya Dubey, Jugal K. Verma

摘要:

设$I$是一个理想,它由一个优良的Cohen-Macaulay局部域中的参数系统生成。我们证明了过滤$\{(I^n)^*: n\in \mathbb{N}\}$的相关分次环$G^*(I)$是Cohen-Macaulay。证明了若$R$是一个优良的Buchsbaum局部整环,则$G^*(I)$是Rees环$\mathcal R^*(I)=\oplus_{n\in \mathbb{N}}(I^n)^*.$上的一个Buchsbaum模。Aberbach、Huneke-Itoh和Huneke-Hochster关于优秀局部域中的过滤$\{(I^n)^*: n\in \mathbb{N}\}$的研究。证明中使用的一个重要工具是M.霍赫斯特和C. Huneke提出了一种新的Cohen-Macaulay代数,它指出了一个优良局部区域的绝对积分闭包是一个大的Cohen-Macaulay代数。本文计算了超曲面环$R=\mathbb{F}_p[X_0,\ldots ,X_d]/(X_0^r+\cdots+X_d^r).$中由齐次参数系$e$生成的$I^n$的紧闭包。在这种情况下,我们证明了$G^*(I)$是Cohen-Macaulay的。给出了Rees代数$r, d, e$为Cohen-Macaulay的条件.

英文摘要:

Let $I$ be an ideal generated by a system of parameters in an excellent Cohen-Macaulay local domain. We show that the associated graded ring $G^*(I)$ of the filtration $\{(I^n)^*: n\in \mathbb{N}\}$ is Cohen-Macaulay. We prove that if $R$ is an excellent Buchsbaum local domain then $G^*(I)$ is a Buchsbaum module over the Rees ring $\mathcal R^*(I)=\oplus_{n\in \mathbb{N}}(I^n)^*.$ We provide quick proofs of well-known results of I. Aberbach, Huneke-Itoh and Huneke-Hochster about the filtration $\{(I^n)^*: n\in \mathbb{N}\}$ in excellent local domains. An important tool used in the proofs is a deep result due to M. Hochster and C. Huneke which states that the absolute integral closure of an excellent local domain is a big Cohen-Macaulay algebra. We compute the tight closure of $I^n$ where $I$ is generated by homogeneous system of parameters having the same degree $e$ in the hypersurface ring $R=\mathbb{F}_p[X_0,\ldots ,X_d]/(X_0^r+\cdots+X_d^r).$ In such cases we prove that $G^*(I)$ is Cohen-Macaulay. We provide conditions on $r, d, e$ for the Rees algebra $\mathcal R^*(I)$ to be Cohen-Macaulay.

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