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Cartan Subalgebra




Cartan subalgebras exist for finite dimensional Lie algebras whenever the base field is infinite. If the field is algebraically closed of characteristic 0 and the algebra is finite dimensional then all Cartan subalgebras are conjugate under automorphisms of the Lie algebra, and in particular are all isomorphic.

A Cartan subalgebra of a finite dimensional semisimple Lie algebra over an Algebraically Closed Field of characteristic 0 is Abelian and
also has the following property of its Eigenspace s of \mathfrak{g} Restricted to \mathfrak{h} diagonalize the representation, and the eigenspace of the zero weight vector is \mathfrak{h}.
The non-zero weights are called the Roots , and the corresponding eigenspaces are called ''' Root Spaces ''', and are all 1-dimensional.

Kac-Moody Algebra s and Generalized Kac-Moody Algebra s also have Cartan subalgebras.

The name is for Élie Cartan .


EXAMPLES


  • Any nilpotent Lie algebra is its own Cartan subalgebra.

  • A Cartan subalgebra of the Lie algebra of ''n''×''n'' matrices over a field is the algebra of all diagonal matrices.

  • The Lie algebra sl2(R) of 2 by 2 matrices of trace 0 has two non-conjugate Cartan subalgebras.



SEE ALSO



REFERENCES

  • Nathan Jacobson , ''Lie algebras'', ISBN 0-486-63832-4

  • J.E. Humphreys, ''Introduction to Lie Algebras and Representation Theory'', ISBN 0-387-90053-5