Linear Lie algebra

In algebra, a linear Lie algebra is a subalgebra [math]\displaystyle{ \mathfrak{g} }[/math] of the Lie algebra [math]\displaystyle{ \mathfrak{gl}(V) }[/math] consisting of endomorphisms of a vector space V. In other words, a linear Lie algebra is the image of a Lie algebra representation. Any Lie algebra is a linear Lie algebra in the sense that there is always a faithful representation of [math]\displaystyle{ \mathfrak{g} }[/math] (in fact, on a finite-dimensional vector space by Ado's theorem if [math]\displaystyle{ \mathfrak{g} }[/math] is itself finite-dimensional.)

Let V be a finite-dimensional vector space over a field of characteristic zero and [math]\displaystyle{ \mathfrak{g} }[/math] a subalgebra of [math]\displaystyle{ \mathfrak{gl}(V) }[/math]. Then V is semisimple as a module over [math]\displaystyle{ \mathfrak{g} }[/math] if and only if (i) it is a direct sum of the center and a semisimple ideal and (ii) the elements of the center are diagonalizable (over some extension field).

References

• Jacobson, Nathan (1979). Lie algebras. New York: Dover Publications, Inc.. ISBN 978-0-486-13679-0. OCLC 867771145. http://www.freading.com/ebooks/details/r:download/ZnJlYWQ6OTc4MDQ4NjEzNjc5MDpl.