Annihilating-Ideal Graphs and Orthogonality Graphs over $\mathbb{F}_2$

Abstract

We construct a family of finite local rings whose annihilating-ideal graphs are naturally described by orthogonality of subspaces of $\mathbb{F}_2^n$. For $n=4$ we determine the clique and chromatic numbers exactly and obtain \[ \omega(\AG(R_4))=5<6=\chi(\AG(R_4)). \] Thus $\AG(R_4)$ is not weakly perfect, and the Behboodi--Rakeei conjecture fails for non-reduced commutative rings.