Finiteness dimensions and cofiniteness of generalized local cohomology modules

Abstract

Let $R$ be a commutative Noetherian ring with non-zero identity, $\mathfrak{a}$ and ideal of $R$, $M$ a finite $R$--module, and $n$ a non-negative integer. In this paper, for an arbitrary $R$--module $X$ which is not necessarily finite, we study the finiteness dimension $f_\mathfrak{a}(M,X)$ and the $n$-th finiteness dimension $f^n_\mathfrak{a}(M,X)$ of $M$ and $X$ with respect to $\mathfrak{a}$. Assume that $\operatorname{Ext}^{i}_{R}(R/\mathfrak{a},X)$ is finite for all $i\leq f^2_\mathfrak{a}(M,X)$ (resp. $i< f^1_\mathfrak{a}(M,X)$). We show that $\operatorname{H}^{i}_{\mathfrak{a}}(M,X)$ is $\mathfrak{a}$--cofinite for all $i< f^2_\mathfrak{a}(M,X)$ (resp. $i< f^1_\mathfrak{a}(M,X)$) and $\operatorname{Ass}_{R}(\operatorname{H}^{f^2_\mathfrak{a}(M,X)}_{\mathfrak{a}}(M,X))$ (resp. if $\operatorname{Ext}^{f^1_\mathfrak{a}(M,X)}_{R}(R/\mathfrak{a},X)$ is finite, then $\operatorname{Ass}_{R}(\operatorname{H}^{f^1_\mathfrak{a}(M,X)}_{\mathfrak{a}}(M,X))$) is finite.