Some criteria for regular and Gorenstein local rings via syzygy modules

Abstract

Let $R$ be a Cohen-Macaulay local ring. We prove that the $n$th syzygy module of a maximal Cohen-Macaulay $R$-module cannot have a semidualizing direct summand for every $n\ge 1$. In particular, it follows that $R$ is Gorenstein if and only if some syzygy of a canonical module of $R$ has a non-zero free direct summand. We also give a number of necessary and sufficient conditions for a Cohen-Macaulay local ring of minimal multiplicity to be regular or Gorenstein. These criteria are based on vanishing of certain Exts or Tors involving syzygy modules of the residue field.

13 pages

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