On the 2-rank and 4-rank of the class group of some real pure quartic number fields

Abstract

Let $K=\mathbb{Q}(\sqrt[4]{p{d}^2})$ be a real pure quartic number field and $k=\mathbb{Q}(\sqrt{p})$ its real quadratic subfield, where $p\equiv 5(\mathrm{mod}8)$ is a prime integer and $d$ an odd square-free integer coprime to $p$. In this work, we calculate $r_2(K)$, the $2$-rank of the class group of $K$, in terms of the number of prime divisors of $d$ that decompose or remain inert in $\mathbb{Q}(\sqrt{p})$, then we will deduce forms of $d$ satisfying $r_2(K)=2$. In the last case, the $4$-rank of the class group of $K$ is given too.

16 pages