Ovoids of Generalized Quadrangles of Order $(q,q^2-q)$ and Delsarte Cocliques in Related Strongly Regular Graphs

We investigate strongly regular graphs for which Hoffman’s ratio bound and Cvetcovi'{c}'s inertia bound are equal. This means that $v{e}^{-}=m^{-}(e^{-}-k)$, where $v$ is the number of vertices, $k$ is the regularity, $e^{-}$ is the smallest eigenvalue, and $m^{-}$ is the multiplicity of $e^{-}$. We show that Delsarte cocliques do not exist for all Taylor’s $2$-graphs and for point graphs of generalized quadrangles of order $(q,q^2-q)$ for infinitely many $q$. For cases where equality may hold, we show that for nearly all parameter sets, there are at most two Delsarte cocliques.