English

Vertex-transitive nut graph order-degree existence problem

Combinatorics 2026-01-14 v3 Number Theory

Abstract

A nut graph is a nontrivial simple graph whose adjacency matrix has a simple eigenvalue zero such that the corresponding eigenvector has no zero entries. It is known that the order nn and degree dd of a vertex-transitive nut graph satisfy 4d4 \mid d, d4d \ge 4, 2n2 \mid n and nd+4n \ge d + 4; or d2(mod4)d \equiv 2 \pmod 4, d6d \ge 6, 4n4 \mid n and nd+6n \ge d + 6. Here, we prove that for each such nn and dd, there exists a dd-regular Cayley nut graph of order nn. As a direct consequence, we obtain all the pairs (n,d)(n, d) for which there is a dd-regular vertex-transitive (resp. Cayley) nut graph of order nn.

Keywords

Cite

@article{arxiv.2507.02481,
  title  = {Vertex-transitive nut graph order-degree existence problem},
  author = {Ivan Damnjanović},
  journal= {arXiv preprint arXiv:2507.02481},
  year   = {2026}
}
R2 v1 2026-07-01T03:44:39.614Z