English

Forbidden subgraphs on conjugacy class graphs of groups

Group Theory 2025-04-02 v4

Abstract

Let GG be a finite group. The \textit{commuting/nilpotent/solvable conjugacy class graph} (ΓCCC(G)\Gamma_{CCC}(G), ΓNCC(G)\Gamma_{NCC}(G), or ΓSCC(G)\Gamma_{SCC}(G)) is a simple graph whose vertex set consists of all non-central conjugacy classes of GG. Two vertices xGx^G and yGy^G are adjacent if and only if there exist elements axGa \in x^G and byGb \in y^G such that a,b\langle a, b \rangle forms an abelian, nilpotent, or solvable subgroup of GG, respectively.\par In this paper, we mainly investigate cographs (it is P4P_4-free), chordal graphs (it is CnC_n-free  n4\forall \ n\ge 4 ), split graphs (it contains no induced subgraph isomorphic to C4, C5C_4,\ C_5, and 2K22K_2), threshold graphs (it contains no induced subgraph isomorphic to P4P_4, C4, C5C_4,\ C_5, and 2K22K_2), and claw-free graphs (it contains no vertex with three pairwise non-adjacent neighbours) in terms of forbidden induced subgraphs in ΓCCC(G)\Gamma_{CCC}(G)/ ΓNCC(G)\Gamma_{NCC}(G)/ΓSCC(G)\Gamma_{SCC}(G).\par We provide a complete classification of these properties for EPPO groups, groups of order pqpq, and nilpotent groups. Additionally, we characterize the induced subgraphs in the commuting conjugacy class graph for symmetric and alternating groups. For solvable groups such as dihedral, dicyclic, and generalized dihedral groups, we establish complete results. Moreover, we fully characterize the graphs for the Mathieu groups M11M_{11}, M12M_{12}, and M22M_{22}, as well as certain minimal simple groups such as Suzuki groups and PSL(3,3)\mathrm{PSL}(3,3). For other minimal simple groups, such as PSL(2,2p)\mathrm{PSL}(2,2^p), PSL(2,3p)\mathrm{PSL}(2,3^p), and PSL(2,p)\mathrm{PSL}(2,p) (where p>3p > 3 and 5p2+15 \mid p^2 + 1), we demonstrate that the solvable conjugacy class graph is always a cograph. Finally, we present several open problems, highlighting further directions for research in this area.

Keywords

Cite

@article{arxiv.2406.01305,
  title  = {Forbidden subgraphs on conjugacy class graphs of groups},
  author = {Papi Ray and Sonakshee Arora},
  journal= {arXiv preprint arXiv:2406.01305},
  year   = {2025}
}

Comments

29 Pages

R2 v1 2026-06-28T16:51:05.692Z