English

On Coefficient ideals

Commutative Algebra 2022-08-26 v1

Abstract

Let (A,m)(A,\mathfrak{m}) be a Cohen-Macaulay local ring of dimension d2d \geq 2 with infinite residue field and let II be an m\mathfrak{m}-primary ideal. For 0id0 \leq i \leq d let IiI_i be the ithi^{th}-coefficient ideal of II. Also let I~=Id\widetilde{I} = I_d denote the Ratliff-Rush closure of AA. Let G=GI(A)G = G_I(A) be the associated graded ring of II. We show that if dimHG+j(G)j1\dim H^j_{G_+}(G)^\vee \leq j -1 for 1jid11 \leq j \leq i \leq d-1 then (In)di=In~(I^n)_{d-i} = \widetilde{I^n} for all n1n \geq 1. In particular if GG is generalized Cohen-Macaulay then (In)1=In~(I^n)_1 = \widetilde{I^n} for all n1n \geq 1. As a consequence we get that if AA is an analytically unramified domain with GG generalized Cohen-Macaulay, then the S2S_2-ification of the Rees algebra A[It] A[It] is n0In~\bigoplus_{n \geq 0} \widetilde{I^n}.

Keywords

Cite

@article{arxiv.2208.12147,
  title  = {On Coefficient ideals},
  author = {Tony J. Puthenpurakal},
  journal= {arXiv preprint arXiv:2208.12147},
  year   = {2022}
}