# Relative crystalline representations and $p$-divisible groups in the small ramification case

## TL;DR

This paper proves that in the case of small ramification, every crystalline Galois representation with Hodge-Tate weights in [0,1] over a certain base ring originates from a $p$-divisible group, extending the understanding of such representations.

## Contribution

It establishes a correspondence between crystalline representations and $p$-divisible groups in the small ramification case, under mild conditions on the base ring.

## Key findings

- Crystalline representations with weights in [0,1] are from $p$-divisible groups when ramification degree e < p-1.
- The result applies to a broad class of relative base rings over $W(k)$.
- Provides a link between Galois representations and algebraic groups in the small ramification setting.

## Abstract

Let $k$ be a perfect field of characteristic $p > 2$, and let $K$ be a finite totally ramified extension over $W(k)[\frac{1}{p}]$ of ramification degree $e$. Let $R_0$ be a relative base ring over $W(k)\langle t_1^{\pm 1}, \ldots, t_m^{\pm 1}\rangle$ satisfying some mild conditions, and let $R = R_0\otimes_{W(k)}\mathcal{O}_K$. We show that if $e < p-1$, then every crystalline representation of $\pi_1^{\text{\'et}}(\mathrm{Spec}R[\frac{1}{p}])$ with Hodge-Tate weights in $[0, 1]$ arises from a $p$-divisible group over $R$.