Two sufficient conditions for non-normal Cayley graphs and their applications

摘要

A Cayley graph Cay(G, S) on a group G is said to be normal if the right regular representation R(G) of G is normal in the full automorphism group of Cay(G, S). In this paper, two sufficient conditions for non-normal Cayley graphs are given and by using the conditions, five infinite families of connected non-normal Cayley graphs are constructed. As an application, all connected non-normal Cayley graphs of valency 5 on A_5 are determined, which generalizes a result about the normality of Cayley graphs of valency 3 or 4 on A_5 determined by Xu and Xu. Further, we classify all non-CI Cayley graphs of valency 5 on A_5, while Xu et al. have proved that A_5 is a 4-CI group.