On the twisted octonionic eigenvalue problem and some sextics hypersurfaces related to the Cartan cubic

Abstract

We revisit the octonionic eigenvalue problem from a geometric perspective. In particular, we study a tautological sheaf defined on a sextic related to this problem, the Ogievetski\^i-Dray-Manogue sextic. We then define and study a twisted version of the octonionic eigenvalue problem. A new sextic arises in this setting and we study the corresponding tautological sheaf supported on it. This twisted version of the octonionic eigenvalue problem is eminently more symmetric than the original one, as reflected by the last result we prove in this paper : the automorphism group of the twisted octonionic eigenvalue problem, though not isomorphic to $\mathrm{E}_6$, acts prehomogeneously on the exceptional Jordan algebra $\mathrm{J}_{3}(\mathbb{O})$. This is in sharp contrast with the fact that the generic orbit for the action of the automorphism group of the classical octonionic eigenvalue problem has (at least) codimension $6$ in $\mathrm{J}_{3}(\mathbb{O})$.