Gauß-Manin connection via Witt-differentials

Abstract

Let $X/R$ be a smooth scheme over a ring $R$. Consider the category of locally free crystals of finite rank on the situs $\mathop{\mathit{Crys}}(X/W_{t}(R))$. We show that it is equivalent to the category of locally free $W_{t}(\mathcal{O}_{X})$-modules of finite rank endowed with a nilpotent, integrable de Rham-Witt connection. In the case where $R$ is a perfect field this was shown by Etesse [E] and Bloch [Bl]We use the result for a construction of the Gauß-Manin connection as a de Rham-Witt connection.