Unitary Graphs


  • Contract grant sponsor: Australian Research Council; Contract grant number: FT110100629.


Unitary graphs are arc-transitive graphs with vertices the flags of Hermitian unitals and edges defined by certain elements of the underlying finite fields. They played a significant role in a recent classification of a class of arc-transitive graphs that admit an automorphism group acting imprimitively on the vertices. In this article, we prove that all unitary graphs are connected of diameter two and girth three. Based on this, we obtain, for any prime power math formula, a lower bound of order math formula on the maximum number of vertices in an arc-transitive graph of degree math formula and diameter two.