English

Weakly cofiniteness of local cohomology modules

Commutative Algebra 2017-07-24 v1

Abstract

Let RR be a commutative Noetherian ring, Φ\Phi a system of ideals of RR and IΦI\in \Phi. Let MM be an RR-module (not necessary II-torsion) such that dimM1\dim M\leq 1, then the RR-module \ExtRi(R/I,M)\Ext^i_{R}(R/I, M) is weakly Laskerian, for all i0i\geq 0, if and only if the RR-module \ExtRi(R/I,M)\Ext^i_{R}(R/I, M) is weakly Laskerian, for i=0,1i=0, 1. Let tN0t\in\Bbb{N}_0 be an integer and MM an RR-module such that \ExtRi(R/I,M)\Ext^i_R(R/I,M) is weakly Laskerian for all it+1i\leq t+1. We prove that if the RR-module \lcΦi(M)\lc^{i}_\Phi(M) is FD1{\rm FD_{\leq 1}} for all i<ti<t, then \lcΦi(M)\lc^{i}_\Phi(M) is Φ\Phi-weakly cofinite for all i<ti<t and for any FD0{\rm FD_{\leq 0}} (or minimax) submodule NN of \lcΦt(M)\lc^t_\Phi(M), the RR-modules \HomR(R/I,\lcΦt(M)/N)\Hom_R(R/I,\lc^t_\Phi(M)/N) and \ExtR1(R/I,\lcΦt(M)/N)\Ext^1_R(R/I,\lc^t_\Phi(M)/N) are weakly Laskerian. Let NN be a finitely generated RR-module. We also prove that \ExtRj(N,\lcΦi(M))\Ext^j_R(N,\lc^{i}_\Phi(M)) and TorjR(N,HΦi(M)){\rm Tor}^R_{j}(N,H^{i}_\Phi(M)) are Φ\Phi-weakly cofinite for all ii and jj whenever MM is weakly Laskerian and \lcΦi(M)\lc^{i}_\Phi(M) is FD1{\rm FD_{\leq 1}} for all ii. Similar results are true for ordinary local cohomology modules and local cohomology modules defined by a pair of ideals.

Keywords

Cite

@article{arxiv.1707.06795,
  title  = {Weakly cofiniteness of local cohomology modules},
  author = {Moharram Aghapournahr},
  journal= {arXiv preprint arXiv:1707.06795},
  year   = {2017}
}

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16 pages