Parametric Decomposition of Powers of Parameter Ideals and Sequentially Cohen-Macaulay Modules

Abstract

Let $M$ be a finitely generated module of dimension $d$ over a Noetherian local ring $(R,\m)$ and $\q $ the parameter ideal generated by a system of parameters $\x = (x_1,..., x_d)$ of $M$. For each positive integer $n$, set $$\Lambda_{d,n}=\{\alpha =(\alpha_1,...,\alpha_d)\in\Bbb{Z}^d|\alpha_i\geqslant 1, \forall 1\leqslant i\leqslant d \text{and} \sum\limits_{i=1}^d\alpha_i=d+n-1\}$$ and $\qa = (x_1^{\alpha_1},...,x_d^{\alpha_d})$. Then we prove in this note that $M$ is a sequentially Cohen-Macaulay module if and only if there exists a certain system of parameters $\x$ such that the equality $\q^nM=\pd$ holds true for all $n$. As an application of this result, we can compute the Hilbert-Samuel polynomial of a sequentially Cohen-Macaulay module with respect to certain parameter ideals