Totally real bi-quadratic fields with large P\'{o}lya groups

TL;DR

This paper constructs infinitely many totally real bi-quadratic fields with Pólya groups of size 2^n, extending previous work and linking to class number divisibility by powers of two.

Contribution

It explicitly constructs infinite families of totally real bi-quadratic fields with Pólya groups of size 2^n, generalizing prior results for the case n=1.

Findings

Existence of infinitely many such fields for each n ≥ 2

Explicit construction of these fields

Connection to class number divisibility by 2^n

Abstract

For an algebraic number field $K$ with ring of integers $\mathcal{O}_{K}$, an important subgroup of the ideal class group $Cl_{K}$ is the {\it P\'{o}lya group}, denoted by $Po(K)$, which measures the failure of the $\mathcal{O}_{K}$-module $Int(\mathcal{O}_{K})$ of integer-valued polynomials on $\mathcal{O}_{K}$ from admitting a regular basis. In this paper, we prove that for any integer $n \geq 2$, there are infinitely many totally real bi-quadratic fields $K$ with $|Po(K)| = 2^{n}$. In fact, we explicitly construct such an infinite family of number fields. This extends an infinite family of bi-quadratic fields with P\'{o}lya group $\mathbb{Z}/2\mathbb{Z}$ given by the authors in \cite{self-ja}. This also provides an infinite family of bi-quadratic fields with class numbers divisible by $2^{n}$.