English

On depth of modules in an ideal

Commutative Algebra 2025-09-23 v2

Abstract

Let RR be a commutative Noetherian ring, II an ideal of RR and MM a finitely generated RR-module with dimR(M)=d\dim_R(M)=d. Denote by \depthR(I,M)\depth_R(I,M) the depth of MM in II. In \cite{HT}, C. Huneke and V. Trivedi proved that if RR is a quotient of a regular ring then there exists a finite subset ΛM\Lambda_M of \Spec(R)\Spec(R) such that \depthR(I,M)=min\pΛM{\depthR\p(M\p)+\docao((I+\p)/\p)}.\depth_R(I,M)=\underset{\p\in \Lambda_M}{\min} \big\{ \depth_{R_{\p}}(M_{\p})+ \docao\big((I+\p)/\p\big) \big\}. Denote by \PsuppRi(M)={p\Spec(R)HpRpidim(R/p)(Mp)0}\Psupp^i_R(M)=\{\frak p\in\Spec(R)\mid H^{i-\dim(R/\frak p)}_{\frak p R_{\frak p}}(M_{\frak p})\neq 0\} the ii-th pseudo support of MM defined by M. Brodmann and R. Y. Sharp \cite{BS1}. In this paper, we prove that if \PsuppRi(M)\Psupp^i_R(M) is closed for all idi\leq d then the above formula of \depthR(I,M)\depth_R(I,M) holds true, where ΛM=0idmin\PsuppRi(M)\Lambda_M =\underset{0\leq i\leq d}{\bigcup} \min \Psupp^i_R(M). In particular, if RR is a quotient of a Cohen-Macaulay local ring then ΛM=0idmin\Var(\AnnR(H\mi(M)))\Lambda_M =\underset{0\leq i\leq d}{\bigcup}\min\Var\big(\Ann_R(H_{\m}^i(M))\big). We also give some examples to clarify the results.

Keywords

Cite

@article{arxiv.2311.04702,
  title  = {On depth of modules in an ideal},
  author = {Tran Nguyen An},
  journal= {arXiv preprint arXiv:2311.04702},
  year   = {2025}
}

Comments

8 pages

R2 v1 2026-06-28T13:15:09.478Z