On quasi-Hermitian varieties in even characteristic and related orthogonal arrays
Angela Aguglia, Luca Giuzzi, Alessandro Montinaro, Viola Siconolfi
TL;DR
This work analyzes BM quasi-Hermitian varieties in $PG(3,q^2)$ for even $q$, showing that all such varieties are projectively equivalent and detailing the full stabilizer groups in $PGL_4(q^2)$ and $PΓL_4(q^2)$. It provides a comprehensive description of the geometric structure, including line incidences, and demonstrates transitivity on affine points, culminating in a complete stabilizer description. As a notable application, the authors construct a simple orthogonal array $OA(q^5,q^4,q,2)$ from the BM varieties, linking finite geometry with experimental design. The results extend the understanding of quasi-Hermitian varieties in even characteristic and offer a concrete bridge to OA-based testing designs.
Abstract
In this paper we study the BM quasi-Hermitian varieties introduced in [A. Aguglia, A. Cossidente, G. Korchmàros, On quasi-Hermitian Varieties, J. Combin. Des. 20 (2012) 433-447.] in characteristc $2$ and dimension $3$. After a brief investigation of their combinatorial properties, we first show that all of these varieties are projectively equivalent, exhibiting a behavior which is strikingly different from what happens in odd characteristic, see [A. Aguglia, L. Giuzzi, On the equivalence of certain quasi-Hermitian varieties, J. Combin. Des. 1-15 (2022)]. This completes the classification project started in that paper. Here we prove more; indeed, by using previous results, we explicitly determine the structure of the full collineation group stabilizing these varieties. Finally, as a byproduct of our investigation, we also construct a family of simple orthogonal arrays $O(q^5,q^4,q,2)$, with entries in $\mathrm{GF}{q}$, where $q$ is an even prime power. Orthogonal arrays (OA's) are principally used to minimize the number of experiments needed in order to investigate how variables in testing interact with each other.
