Indecomposable Algebraic Integers

Abstract

In algebraic number theory, the finiteness of the Picard group of an order in a number field is generally proved via a lattice argument: the order forms a lattice and every ideal class contains an integral ideal with a small enough non-zero element. In this work we will consider $\overline{\mathbb{Z}}$, the ring of algebraic integers, which is a lattice in a similar sense, and we will treat this lattice as intrinsically interesting. We will prove several properties of $\overline{\mathbb{Z}}$ and state some open problems. Many of these properties have connections to the indecomposable elements of the lattice, and our main result regards the decidability of the question whether an algebraic integer is indecomposable.