Tor as a Module over an Exterior Algebra

Let $S$ be a regular local ring with residue field $k$ and let $M$ be a finitely generated $S$-module. Suppose that $f_1,\dots ,f_c\in S$ is a regular sequence that annihilates $M$, and let $E$ be an exterior algebra over $k$ generated by $c$ elements. The homotopies for the $f_{i}$ on a free resolution of $M$ induce a natural structure of graded $E$-module on ${\rm Tor}^{S}(M,k)$. In the case where $M$ is a high syzygy over the complete intersectionR:=S/(f_{1},\dots,f_{c})$we describe this$E$-module structure in detail, including its minimal free resolution over$E$. Turning to${\rm Ext}_{R}(M,\, k)$we show that, when$M$is a high syzygy over$R$, the minimal free resolution of${\rm Ext}_{R}(M,\, k)$as a module over the ring of CI operators is the Bernstein-Gel'fand-Gel'fand dual of the$E$-module${\rm Tor}^{S}(M,\,k)$. For the proof we introduce \emph{higher CI operators}, and give a construction of a (generally non-minimal) resolution of$M$over$S$starting from a resolution of$M$over$R$ and its higher CI operators.