Breuil-Kisin Modules via crystalline cohomology

TL;DR

This paper introduces a new cohomological method to construct Breuil-Kisin modules associated with p-adic étale cohomology for certain formal schemes, under specific conditions on p and the cohomology.

Contribution

It provides a novel cohomological construction of Breuil-Kisin modules and proves its validity in cases where p>2, i<p-1, and the crystalline cohomology is torsion-free.

Findings

Construction works for p>2, i<p-1

Validates the approach under torsion-free crystalline cohomology

Connects étale and crystalline cohomology via new methods

Abstract

For a perfect field $k$ of characteristic $p>0$ and a smooth and proper formal scheme $\mathscr{X}$ over the ring of integers of a finite and totally ramified extension $K$ of $W(k)[1/p]$, we propose a cohomological construction of the Breuil-Kisin modules attached to the $p$-adic \'etale cohomology $H^i_{\mathrm{\'et}}(\mathscr{X}_{\overline{K}},\mathbf{Z}_p)$. We then prove that our proposal works when $p>2$, $i < p-1$, and the crystalline cohomology of the special fiber of $\mathscr{X}$ is torsion-free in degrees $i$ and $i+1$.