On reducible Killing forms for groups of Lie type

Killing forms on finite groups arise as examples of braided Killing forms on braided Lie algebras. For a finite group $G$ and a $G$-stable subset $\mathcal{C}$, the Killing form associated with $\mathbb{C}[\mathcal{C}]$ is given by $K_{\mathcal{C}}(a,b)=\mathrm{\mid }{C}_G(ab)\cap \mathcal{C}\mathrm{\mid }$ for $a,b\in \mathcal{C}$. Motivated by Cartan’s criterion for semisimplicity of Lie algebras, and previous work of López Peña, Majid, and Rietsch, we study the non-degeneracy and irreducibility of $K_{\mathcal{C}}$ when $\mathcal{C}$ is a conjugacy class of involutions or unipotent elements in a finite simple group of Lie type and Lie rank one. Our approach suggests interesting connections with character theory, related counting formulas, and the study of commuting graphs.