On triangles in derangement graphs

Abstract

Given a permutation group $G$, the derangement graph $\Gamma_G$ of $G$ is the Cayley graph with connection set the set of all derangements of $G$. We prove that, when $G$ is transitive of degree at least $3$, $\Gamma_G$ contains a triangle. The motivation for this work is the question of how large can be the ratio of the independence number of $\Gamma_G$ to the size of the stabilizer of a point in $G$. We give examples of transitive groups where this ratio is maximum.