Detecting finite flat dimension of modules via iterates of the Frobenius endomorphism (1612.00509v2)

Abstract: It is proved that a module $M$ over a Noetherian ring $R$ of positive characteristic $p$ has finite flat dimension if there exists an integer $t\ge 0$ such that $\operatorname{Tor}i^R(M, {}^{f^{e}}!R)=0$ for $t\le i\le t+\dim R$ and infinitely many $e$. This extends a result of Herzog, who proved it when $M$ is finitely generated, and strengthens a result of the third author and Webb in the case $M$ is arbitrary. It is also proved that when $R$ is a Cohen-Macaulay local ring, it suffices that the Tor vanishing holds for one $e\ge \log{p}e(R)$, where $e(R)$ is the multiplicity of $R$.