Discriminant-Stability in $p$-adic Lie Towers of Number Fields

Abstract

In this paper we consider a tower of number fields $\cdots \supseteq K(1)\supseteq K(0)\supseteq K$ arising naturally from a continuous $p$-adic representation of $\mathrm{Gal}(\bar{\mathbb{Q}}/K)$, referred to as a $p$-adic Lie tower over $K$. A recent conjecture of Daqing Wan hypothesizes, for certain $p$-adic Lie towers of curves over ${\mathbb{F}}_p$, a stable (polynomial) growth formula for the genus. Here we prove the analogous result in characteristic zero, namely: the $p$-adic valuation of the discriminant of the extension $K(i)/K$ is given by a polynomial in $i,p^i$ for $i$ sufficiently large. This generalizes a previously known result on discriminant-growth in ${\mathbb{Z}}_p$-towers of local fields of characteristic zero.