English

Maximal Cohen-Macaulay modules that are not locally free on the punctured spectrum

Commutative Algebra 2020-01-13 v2

Abstract

We say that a Cohen-Macaulay local ring has finite CM+\operatorname{\mathsf{CM}}_+-representation type if there exist only finitely many isomorphism classes of indecomposable maximal Cohen-Macaulay modules that are not locally free on the punctured spectrum. In this paper, we consider finite CM+\operatorname{\mathsf{CM}}_+-representation type from various points of view, relating it with several conjectures on finite/countable Cohen-Macaulay representation type. We prove in dimension one that the Gorenstein local rings of finite CM+\operatorname{\mathsf{CM}}_+-representation type are exactly the local hypersurfaces of countable CM\mathsf{CM}-representation type, that is, the hypersurfaces of type (A)(\mathrm{A}_\infty) and (D)(\mathrm{D}_\infty). We also discuss the closedness and dimension of the singular locus of a Cohen-Macaulay local ring of finite CM+\operatorname{\mathsf{CM}}_+-representation type.

Keywords

Cite

@article{arxiv.1903.03287,
  title  = {Maximal Cohen-Macaulay modules that are not locally free on the punctured spectrum},
  author = {Toshinori Kobayashi and Justin Lyle and Ryo Takahashi},
  journal= {arXiv preprint arXiv:1903.03287},
  year   = {2020}
}

Comments

24 pages. Minor corrections made throughout