English

Bass and Betti Numbers of $A/I^n.$

Commutative Algebra 2019-09-10 v1

Abstract

Let (A,\m,k)(A, \m, k) be a Gorenstein local ring of dimension d1. d\geq 1. Let II be an ideal of AA with \htt(I)d1.\htt(I) \geq d-1. We prove that the numerical function n(\extAi(k,A/In+1)) n \mapsto \ell(\ext_A^i(k, A/I^{n+1})) is given by a polynomial of degree d1d-1 in the case when id+1 i \geq d+1 and \curv(In)>1\curv(I^n) > 1 for all n1.n \geq 1. We prove a similar result for the numerical function n(\ToriA(k,A/In+1)) n \mapsto \ell(\Tor_i^A(k, A/I^{n+1})) under the assumption that AA is a \CM ~ local ring. \noindent We note that there are many examples of ideals satisfying the condition \curv(In)>1,\curv(I^n) > 1, for all n1. n \geq 1. We also consider more general functions n(\ToriA(M,A/In)n \mapsto \ell(\Tor_i^A(M, A/I_n) for a filtration {In}\{I_n \} of ideals in A.A. We prove similar results in the case when MM is a maximal \CM ~ AA-module and {In=In}\{I_n=\overline{I^n} \} is the integral closure filtration, II an \m\m-primary ideal in A.A.

Keywords

Cite

@article{arxiv.1909.03869,
  title  = {Bass and Betti Numbers of $A/I^n.$},
  author = {Ganesh S. Kadu and Tony J. Puthenpurakal},
  journal= {arXiv preprint arXiv:1909.03869},
  year   = {2019}
}