Cliques in graphs constructed from Strongly Orthogonal Subsets in exceptional root systems
Abstract
Given a root system , two roots are said to be \emph{strongly orthogonal} if neither their sum nor difference is a root. Gashi defined a family of graphs with vertices labelled by sums of -element strongly orthogonal subsets of roots, and edges connect vertices whose difference is also a vertex. Gashi and the current authors established Erd\H{o}s--Ko--Rado type results for graphs developed from Type root systems. In this paper, we study graphs developed from the exceptional root systems , , , , and . We compute graph-theoretic invariants including regularity, connectivity, and clique numbers, and analyze clique structures with respect to sunflower properties. The automorphism group contains the Weyl group; we use these symmetries to obtain complete counts of maximum cliques and maximum sunflowers. Unlike type , where all maximal cliques are sunflowers for large rank, sunflower cliques comprise at most 11\% of maximum cliques in the simply-laced exceptional types , , and .
Keywords
Cite
@article{arxiv.2604.02983,
title = {Cliques in graphs constructed from Strongly Orthogonal Subsets in exceptional root systems},
author = {Patrick J. Browne and Pádraig Ó Catháin},
journal= {arXiv preprint arXiv:2604.02983},
year = {2026}
}
Comments
12 pages