Constructing abelian extensions with prescribed norms

Abstract:

Given a number field $K$, a finite abelian group $G$ and finitely many elements $\alpha _1,\ldots ,\alpha _t\in K$, we construct abelian extensions $L/K$ with Galois group $G$ that realise all of the elements $\alpha _1,\ldots ,\alpha _t$ as norms of elements in $L$. In particular, this shows existence of such extensions for any given parameters.

Our approach relies on class field theory and a recent formulation of Tate’s characterisation of the Hasse norm principle, a local-global principle for norms. The constructions are sufficiently explicit to be implemented on a computer, and we illustrate them with concrete examples.