Strongly divisible lattices and crystalline cohomology in the imperfect residue field case

Abstract

Let $k$ be a perfect field of characteristic $p \geq 3$, and let $K$ be a finite totally ramified extension of $K_0 = W(k)[p^{-1}]$. Let $L_0$ be a complete discrete valuation field over $K_0$ whose residue field has a finite $p$-basis, and let $L = L_0\otimes_{K_0} K$. For $0 \leq r \leq p-2$, we classify $\mathbf{Z}_p$-lattices of semistable representations of $\mathrm{Gal}(\overline{L}/L)$ with Hodge-Tate weights in $[0, r]$ by strongly divisible lattices. This generalizes the result of Liu. Moreover, if $\mathcal{X}$ is a proper smooth formal scheme over $\mathcal{O}_L$, we give a cohomological description of the strongly divisible lattice associated to $H^i_{\text{\'et}}(\mathcal{X}_{\overline{L}}, \mathbf{Z}_p)$ for $i \leq p-2$, under the assumption that the crystalline cohomology of the special fiber of $\mathcal{X}$ is torsion-free in degrees $i$ and $i+1$. This generalizes a result in Cais-Liu.