A characterization of Eisenstein polynomials generating cyclic extensions of degree $p^2$ and $p^3$ over an unramified $\kp$-adic field

Abstract

Let $p\neq2$ be a prime. We show a technique based on local class field theory and on the expansions of certain resultants which allows to recover very easily Lbekkouri's characterization of Eisenstein polynomials generating cyclic wild extensions of degree $p^2$ over $\Q_p$, and to extend it to the case of the base field $K$ being an unramified extension of $\Q_p$. Furthermore, when a polynomial satisfies only some of the stated conditions, we show that the first unsatisfied condition gives information about the Galois group of the normal closure. This permits to give a complete classification of Eisenstein polynomials of degree $p^2$ whose splitting field is a $p$-extension, providing a full description of the Galois group and its higher ramification subgroups. We then apply the same methods to give a characterization of Eisenstein polynomials of degree $p^3$ generating a cyclic extension. In the last section we deduce a combinatorial interpretation of the monomial symmetric function evaluated in the roots of the unity which appear in certain expansions.