On gradings modulo 2 of simple Lie algebras in characteristic 2

Abstract

The ground field in the text is of characteristic 2. The classification of modulo 2 gradings of simple Lie algebras is vital for the classification of simple finite dimensional Lie superalgebras: with each grading, a simple Lie superalgebra is associated, see arXiv:1407.1695. No classification of gradings was known for any type of simple Lie algebras, bar restricted Zassenhaus algebras (a.k.a. Witt algebras, i.e., Lie algebras of vector fields with truncated polynomials as coefficients) on not less than 3 indeterminates. Here (under an assumption about their algebras of derivations) we completely describe gradings modulo 2 for several series of simple (relatives of the) Lie algebras: of special linear series (except for \(\mathfrak{psl}(4)\) for which a conjecture is given), two inequivalent orthogonal, and projectivizations of their derived Lie algebras. The classification of gradings is new but all of the corresponding superizations are known. For the Zassenhaus algebras on one indeterminate of height \(n>1\), there is an \((n-2)\)-parametric family of modulo 2 gradings; all but one of the corresponding simple Lie superalgebras are new. Our classification yields non-triviality of a deformation of a simple \((3|2)\)-dimensional Lie superalgebra (new result).