Non-associative Frobenius algebras of type $G_2$ and $F_4$

Abstract

Very recently, Maurice Chayet and Skip Garibaldi have introduced a class of commutative non-associative algebras, for each simple linear algebraic group over an arbitrary field (with some minor restriction on the characteristic). We give an explicit description of these algebras for groups of type $G_2$ and $F_4$ in terms of the octonion algebras and the Albert algebras, respectively. As a byproduct, we determine all possible invariant commutative algebra products on the representation with highest weight $2{\omega }_1$ for $G_2$ and on the representation with highest weight $2{\omega }_4$ for $F_4$. It had already been observed by Chayet and Garibaldi that the automorphism group for the algebras for type $F_4$ is equal to the group of type $F_4$ itself. Using our new description, we are able to show that the same result holds for type $G_2$.

arXiv comment31 pages, corrected some typos and added some remarks suggested by an anonymous referee. Moreover, Proposition 4.6 has been extended to the Lie algebra to prove Corollary 4.7