New Bounds for Partial Spreads of $H(2d-1,q^2)$ and Partial Ovoids of the Ree-Tits Octagon

Abstract

Two results are obtained that give upper bounds on partial spreads and partial ovoids respectively. The first result is that the size of a partial spread of the Hermitian polar space $\mathsf{H}(3,q^2)$ is at most ${\left(\frac{2p^3+p}{3}\right)}^t+1$, where $q=p^t$, $p$ is a prime. For fixed $p$ this bound is in $o(q^3)$, which is asymptotically better than the previous best known bound of $(q^3+q+2)/2$. Similar bounds for partial spreads of $\mathsf{H}(2d-1,q^2)$, $d$ even, are given. The second result is that the size of a partial ovoid of the Ree-Tits octagon $\mathsf{O}(2^t)$ is at most $26^t+1$. This bound, in particular, shows that the Ree-Tits octagon $\mathsf{O}(2^t)$ does not have an ovoid.

arXiv comment8 pages, corrected a false claim on collineations in the Ree-Tits octagon, see arXiv:2002.07977v1 [math.GR], Remark 2.3