The fields generated by character values of linear and unitary groups

Abstract: For a finite group $G$, define the field $$\mathbb{Q}(G) := \mathbb{Q}({χ(g) : χ\in \operatorname{Irr}(G) , g \in G})$$. In this article we compute generating sets for the fields $\mathbb{Q}(G)$ when $G$ is a finite general or special linear group, a finite general or special unitary group, or one of the simple groups $\operatorname{PSL}_n(q)$ or $\operatorname{PSU}_n(q)$. We then apply these results to classify all number fields $F$ of degree $2$ or $3$ over $\mathbb{Q}$ such that $F = \mathbb{Q}(S)$ for some non-abelian simple group $S$.