Hilbert genus fields of biquadratic fields

Abstract

The Hilbert genus field of the real biquadratic field $K = \mathbb{Q}\left( {\sqrt \delta ,\sqrt d } \right)$ is described by Yue (2010) and Bae and Yue (2011) explicitly in the case δ = 2 or p with p ≡ 1 mod 4 a prime and d a squarefree positive integer. In this article, we describe explicitly the Hilbert genus field of the imaginary biquadratic field $K = \mathbb{Q}\left( {\sqrt \delta ,\sqrt d } \right)$, where δ = −1,−2 or −p with p ≡ 3mod 4 a prime and d any squarefree integer. This completes the explicit construction of the Hilbert genus field of any biquadratic field which contains an imaginary quadratic subfield of odd class number.