On the relative Cohen-Macaulay modules (1303.2208v2)

Abstract: Let $R$ be a commutative Noetherian local ring and let $\fa$ be a proper ideal of $R$. A non-zero finitely generated $R$-module $M$ is called relative Cohen-Macaulay with respect to $\fa$ if there is precisely one non vanishing local cohomology modules $\H_{\fa}^{i}(M)$ of $M$. In this paper, as a main result, it is shown that if $M$ is a Gorenstein $R$--module, then $\H_{\fa}^{i}(M)=0$ for all $i\neq c$ where $c=\h_{M}\fa$ is completely encoded in homological properties of $\H_{\fa}^{c}(M)$, in particular in its Bass numbers. Notice that, this result provides a generalization of a result of M. Hellus and P. Schenzel which has been proved before, as a main result, in the case where $M=R$.