Toral Lie algebra

In mathematics, a toral Lie algebra is a Lie subalgebra of a general linear Lie algebra all of whose elements are semisimple (or diagonalizable over an algebraically closed field). Equivalently, a Lie algebra is toral if it contains no nonzero nilpotent elements. Over an algebraically closed field, every toral Lie algebra is abelian; thus, its elements are simultaneously diagonalizable.

Semisimple and reductive Lie algebras

A subalgebra H of a semisimple Lie algebra L is called toral if the adjoint representation of H on L, ad(H)⊂gl(L) is a toral Lie algebra. A maximal toral Lie subalgebra of a finite-dimensional semisimple Lie algebra, or more generally of a finite-dimensional reductive Lie algebra, over an algebraically closed field of characteristic 0 is a Cartan subalgebra and vice versa. In particular, a maximal toral Lie subalgebra in this setting is self-normalizing, coincides with its centralizer, and the Killing form of L restricted to H is nondegenerate.

For more general Lie algebras, a Cartan algebra may differ from a maximal toral algebra.

See also

• Maximal torus, in the theory of Lie groups

References

• Borel, Armand (1991), Linear algebraic groups, Graduate Texts in Mathematics 126 (2nd ed.), Berlin, New York: Springer-Verlag, ISBN 978-0-387-97370-8, MR 1102012
• Humphreys, James E. (1972), Introduction to Lie Algebras and Representation Theory, Berlin, New York: Springer-Verlag, ISBN 978-0-387-90053-7