On the non-existence of sympathetic Lie algebras with dimension less than 25

Citation

Garcia Pulido AL & Salgado G (2023) On the non-existence of sympathetic Lie algebras with dimension less than 25. Journal of Algebra and Its Applications. https://doi.org/10.1142/S0219498825501221

Abstract
In this article we investigate the question of the lowest possible dimension that a sympathetic Lie algebra g can attain, when its Levi subalgebra gL is simple. We establish the structure of the nilradical of a perfect Lie algebra g, as a gL-module, and determine the possible Lie algebra structures that one such g admits. We prove that, as a gL-module, the nilradical must decompose into at least 4 simple modules. We explicitly calculate the semisimple derivations of a perfect Lie algebra g with Levi sub-algebra gL=sl2(C) and give necessary conditions for g to be a sympathetic Lie algebra in terms of these semisimple derivations. We show that there is no sympathetic Lie algebra of dimension lower than 15, independently of the nilradical’s decomposition. If the nilradical has 4 simple modules, we show that a sympathetic Lie algebra has dimension greater or equal than 25.

Keywords
Sympathetic Lie algebras; equivariant maps; inner derivations

Journal
Journal of Algebra and Its Applications