Cameron-Liebler Sets for 2-Transitive Groups

Abstract

This research was conducted on 2-transitive groups whose minimal normal subgroup is abelian. Suppose G is such a group and ΓG is its derangement graph. Any maximum coclique S of ΓG has a characteristic vector xS. Each xS is a boolean vector contained in a particular module, which is called the permutation module MP. This module has a dimension of 1 + (n − 1)2, where n = deg(G), and it is spanned by {xij | i,j∈{1,...,n}}, where each xij is the characteristic vector of Sij, the set of permutations that map i to j. Apart from the xij, which correspond to the stabilizers of G and their cosets, this research set out to find any other boolean vectors that are contained in Mp using linear programming. Henceforth, such boolean vectors are defined to be Cameron-Liebler sets for 2-transitive groups. In addition to finding Cameron-Liebler sets, analyses were performed on each group to determine: (1) whether the strict EKR property holds; (2) the number of maximum cocliques that are subgroups, cosets, or neither; (3) isomorphism classes and conjugacy classes of the maximum cocliques that are subgroups; (4) the dimension of C′, the maximum cliques that are subgroups (along with their right cosets), and C, all maximum cliques; and (5) the spectrum of ΓG and whether the ratio bound is satisfied with equality.