English

Cohen-Macaulay approximations over generically Gorenstein rings

Commutative Algebra 2026-03-24 v1

Abstract

Let (R,m)(R,\mathfrak{m}) be a Cohen-Macaulay local ring with canonical module that is generically Gorenstein. In this paper, I prove isomorphisms relating the minimal MCM approximations and minimal FID hulls of modules constructed from a canonical ideal ωR\,\omega \subset R, including ω/xR\,\omega/xR, with xω\,x \in \omega\, a nonzerodivisor, (ω/xR):=ExtR1(ω/xR,ω)\,(\omega/xR)^{\vee}:=\text{Ext}^1_R(\omega/xR,\omega), R/ω2\,R/\omega^2, and ω/ω2\,\omega/\omega^2. I also prove that if RR is not Gorenstein, then δR(ω/xR)=δR((ω/xR))=0\delta_{R}\left(\omega/xR \right)=\delta_{R}\left(\left(\omega/xR \right)^{\vee} \right)=0\, and γR(ΩR1(ω/xR))=γR(ΩR1((ω/xR)))=0\,\gamma_{R}\left(\Omega^{1}_{R}\left(\omega/xR \right) \right)=\gamma_{R}\left(\Omega^{1}_{R}\left(\left(\omega/xR\right)^{\vee}\right) \right)=0, where δR\delta_R is Auslander's δ\,\delta-invariant and γR\gamma_R is the dual γ\gamma-invariant.

Keywords

Cite

@article{arxiv.2603.21587,
  title  = {Cohen-Macaulay approximations over generically Gorenstein rings},
  author = {Richard F. Bartels},
  journal= {arXiv preprint arXiv:2603.21587},
  year   = {2026}
}

Comments

18 pages

R2 v1 2026-07-01T11:32:44.611Z