ON THE ORDER OF ARC-STABILIZERS IN ARC-TRANSITIVE GRAPHS

Abstract

AbstractLet p be a prime. We say that a transitive action of a group L on a set Ω is p-sub-regular if there exist x,y∈Ω such that 〈Lx,Ly〉=L and LYx≅ℤp, where Y =yLx is the orbit of y under Lx. Our main result is that if Γ is a G-arc-transitive graph and the permutation group induced by the action of Gv on Γ(v) is p-sub-regular, then the order of a G-arc-stabilizer is equal to ps−1 where s≤7, s≠6, and moreover, if p=2, then s≤5. This generalizes a classical result of Tutte on cubic arc-transitive graphs as well as some more recent results. We also give a characterization of p-sub-regular actions in terms of arc-regular actions on digraphs and discuss some interesting examples of small degree.