Galois scaffolds and Galois module structure in extensions of characteristic $p$ local fields of degree $p^2$

TL;DR

This paper investigates the existence of Galois scaffolds in degree p^2 extensions of characteristic p local fields, providing conditions for their existence and analyzing the Galois module structure of the ring of integers.

Contribution

It offers a sufficient condition for Galois scaffold existence in degree p^2 extensions and characterizes the Galois module structure of the ring of integers under these conditions.

Findings

A sufficient condition for Galois scaffold existence in degree p^2 extensions.

Necessary and sufficient conditions for the ring of integers to be free over its associated order.

Explicit determination of Galois module structure in these extensions.

Abstract

A Galois scaffold, in a Galois extension of local fields with perfect residue fields, is an adaptation of the normal basis to the valuation of the extension field, and thus can be applied to answer questions of Galois module structure. Here we give a sufficient condition for a Galois scaffold to exist in fully ramified Galois extensions of degree $p^2$ of characteristic $p$ local fields. This condition becomes necessary when we restrict to $p=3$. For extensions $L/K$ of degree $p^2$ that satisfy this condition, we determine the Galois module structure of the ring of integers by finding necessary and sufficient conditions for the ring of integers of $L$ to be free over its associated order in $K[Gal(L/K)]$.