Cunha, Isabel; Elduque, Alberto: an Extended Freudenthal Magic Square in Characteristic 3. J. Algebra 317, No. 2, 471-509 (2007)

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Cunha, Isabel; Elduque, Alberto: An extended Freudenthal magic square in characteristic 3. J. Algebra 317, No. 2, 471-509 (2007). Mathematics Subject Classification 2000: *17B50, 17B75, 17B20, 17B25, 17B60 Keywords: Tits construction; unital composition algebra; central simple Jordan algebra of degree three; exceptional simple Lie algebra; Freudenthal magic square; exceptional classical Lie superalgebra; triality; characteristic three; extended Freudenthal magic square; contragredient Lie superalgebra Reviewer: JörgFeldvoss (8086) The well-known Tits construction builds a Lie algebra from a unital composition algebra, a central simple Jordan algebra of degree three, and their Lie algebras of inner derivations. This construction is valid over arbitrary fields of characteristic not two or three and all the exceptional simple Lie algebras can be realized in this way. G. Benkart and E. Zelmanov [Invent. Math. 126, No.1, 1-45 (1996; Zbl. 0871.17024)] as well as G. Benkart and the second author of the paper under review [Q. J. Math. 54, No. 2, 123-137 (2003; Zbl. 1045.17002)] extended the Tits construction and the Freudenthal magic square to some of the exceptional classical Lie superalgebras. More recently, C. H. Barton and A. Sudbery [Adv. Math. 180, No. 2, 596-647 (2003; Zbl. 1077.1701)] as well as J. M. Landsberg and L. Manivel [Adv. Math. 171, No. 1, 59-85 (2002; Zbl. 1035.17016)] describe the exceptional simple Lie algebras as octonionic analogues of the classical matrix Lie algebras based on two composition algebras and their Lie algebras of triality. This leads to an alternative construction of the Freudenthal magic square and thereby explains its symmetry. Another advan- tage of this construction is that it remains valid over fields of characteristic three. Moreover, non-trivial composition superalgebras (i.e., with non-zero odd part) only exist in characteristic three and dimensions three or six. Using the latter in the construction of Barton and Sudbery yields an extended Freudenthal magic square in which Lie superalgebras appear. The aim of the paper under review is to give an explicit description of these Lie superalgebras which are either simple or contain a simple ideal of codimension one and with only a single exception have no counterpart in characteristic zero. Furthermore, all the split Lie superalgebras in the extended Freudenthal magic square are described as contragredient Lie superalgebras..

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