On Classifying Extensions of $p$-adic Fields

Abstract

Let $p$ be a prime and let ${\mathbb{Q}}_p$ be the field of $p$-adic numbers. It is known that the finite extensions of ${\mathbb{Q}}_p$ of a given degree are finite up to isomorphism. Given a cubic field extension $L$ of ${\mathbb{Q}}_p$ generated by the root of an irreducible polynomial $h$, we present a practical (closed-form) method to determine the isomorphism class in which $L$ lives, based on the coefficients of $h$. We discuss the subtleties of the wildly ramified case, when the degree of the extension coincides with $p$, the characteristic of the residue field. We also present a method for tamely ramified extensions of arbitrary prime degree.

20 pages, 2 figures