Paley-like graphs over finite fields from vector spaces

Lucas Reis

Published 2022-10-06Version 1

Motivated by the well-known Paley graphs over finite fields and their generalizations, in this paper we explore a natural multiplicative-additive analogue of such graphs arising from vector spaces over finite fields. Namely, if $n\ge 2$ and $U\subsetneq \mathbb F_{q^n}$ is an $\mathbb F_q$-vector space, $G_{U}$ is the (undirected) graph with vertex set $V(G_U)=\mathbb F_{q^n}$ and edge set $E(G_U)=\{(a, b)\in \mathbb F_{q^n}^2\,|\, a\ne b, ab\in U\}$. We describe the structure of an arbitrary maximal clique in $G_U$ and provide bounds on the clique number $\omega(G_U)$ of $G_U$. In particular, we compute the largest possible value of $\omega(G_U)$ for arbitrary $q$ and $n$. Moreover, we obtain the exact value of $\omega(G_U)$ when $U\subsetneq \mathbb F_{q^n}$ is any $\mathbb F_q$-vector space of dimension $d_U\in \{1, 2, n-1\}$.