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arXiv · 2603.17649

Homogeneous Freudenthal algebras and the first Tits construction

Holger P. Petersson·Maneesh Thakur
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Abstract

Freudenthal algebras over a field are basically the same as Jordan algebras of degree $3$ remaining simple under all base field extensions. These algebras are intimately linked, via their automorphism groups and structure groups, to simple algebraic groups over arbitrary fields. Our main concern here will be the question of when these algebras are homogeneous in the sense that all their Jordan isotopes are isomorphic. We answer this question by presenting various necessary and sufficient conditions for homogeneity and by connecting it with the first Tits construction of cubic Jordan algebras, most notably through investigating Freudenthal division algebras over complete fields under a discrete valuation. We also study the first Tits construction in its own right by producing a local version of it, deriving a local-global principle, and by connecting it with the embeddibility of certain rank-$2$-tori into the automorphism group scheme of an Albert division algebra.

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Holger P. Petersson, Maneesh Thakur. 2026-03-18. Homogeneous Freudenthal algebras and the first Tits construction. https://arxiv.org/abs/2603.17649

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