On Bruen chains

Abstract

It is known that a Bruen chain of the three-dimensional projective space $\mathrm{PG}(3,q)$ exists for every odd prime power q at most 37, except for $q=29$. It was shown by Cardinali et al. (2005) that Bruen chains do not exist for $41⩽q⩽49$. We develop a model, based on finite fields, which allows us to extend this result to $41⩽q⩽97$, thereby adding more evidence to the conjecture that Bruen chains do not exist for $q>37$. Furthermore, we show that Bruen chains can be realised precisely as the $(q+1)/2$-cliques of a two related, yet distinct, undirected simple graphs.