On finite generalized quadrangles with $\mathrm{PSL}(2,q)$ as an automorphism group

Abstract

Let $\mathcal{S}$ be a finite thick generalized quadrangle, and suppose that $G$ is an automorphism group of $\mathcal{S}$. If $G$ acts primitively on both the points and lines of $\mathcal{S}$, then it is known that $G$ must be almost simple. In this paper, we show that if the socle of $G$ is $\mathrm{PSL}(2,q)$ with $q\ge 4$, then $q=9$ and $\mathcal{S}$ is the unique generalized quadrangle of order $2$.