Remarks on singular Cayley graphs and vanishing elements of simple groups

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Let Γ be a finite graph and let A(Γ) be its adjacency matrix. Then Γ is singular if A(Γ) is singular. The singularity of graphs is of certain interest in graph theory and algebraic combinatorics. Here we investigate this problem for Cayley graphs Cay(G,H) when G is a finite group and when the connecting set H is a union of conjugacy classes of G. In this situation, the singularity problem reduces to finding an irreducible character χ of G for which ∑h∈Hχ(h)=0. At this stage, we focus on the case when H is a single conjugacy class hG of G; in this case, the above equality is equivalent to χ(h)=0 . Much is known in this situation, with essential information coming from the block theory of representations of finite groups. An element h∈G is called vanishing if χ(h)=0 for some irreducible character χ of G. We study vanishing elements mainly in finite simple groups and in alternating groups in particular. We suggest some approaches for constructing singular Cayley graphs.
Original languageEnglish
Pages (from-to)379-401
Number of pages23
JournalJournal of Algebraic Combinatorics
Issue number4
Early online date30 Nov 2018
Publication statusPublished - Dec 2019


  • Singular Cayley graphs
  • Vertex transitive graphs
  • Vanishing elements
  • Block theory of symmetric and alternating groups

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