Covering groups of $M_{22}$ as regular Galois groups over $\mathbb{Q}$

Abstract

We close a gap in the literature by showing that the full covering groups of the Mathieu group $M_{22}$ and of its automorphism group $Aut(M_{22})$ occur as the Galois group of $\mathbb{Q}$-regular Galois extensions of $\mathbb{Q}(t)$.