Gorenstein rings via homological dimensions, and symmetry in vanishing of Ext and Tate cohomology
Dipankar Ghosh, Tony J. Puthenpurakal
Abstract
The aim of this article is to consider the spectral sequences induced by tensor-hom adjunction, and provide a number of new results. Let $R$ be a commutative Noetherian local ring of dimension $d$. In the 1st part, it is proved that $R$ is Gorenstein if and only if it admits a nonzero CM (Cohen-Macaulay) module $M$ of finite Gorenstein dimension $g$ such that ${\rm type}(M) \le μ( {\rm Ext}_R^g(M,R) )$ (e.g., ${\rm type}(M)=1$). This considerably strengthens a result of Takahashi. Moreover, we show that if there is a nonzero $R$-module $M$ of depth $\ge d - 1$ such that the injective dimensions of $M$, ${\rm Hom}_R(M,M)$ and ${\rm Ext}_R^1(M,M)$ are finite, then $M$ has finite projective dimension and $R$ is Gorenstein. In the 2nd part, we assume that $R$ is CM with a canonical module $ω$. For CM $R$-modules $M$ and $N$, we show that the vanishing of one of the following implies the same for others: ${\rm Ext}_R^{\gg 0}(M,N^{+})$, ${\rm Ext}_R^{\gg 0}(N,M^{+})$ and ${\rm Tor}_{\gg 0}^R(M,N)$, where $M^{+}$ denotes ${\rm Ext}_R^{d-\dim(M)}(M,ω)$. This strengthens a result of Huneke and Jorgensen. Furthermore, we prove a similar result for Tate cohomologies under the additional condition that $R$ is Gorenstein.