 Langlands dual group

In representation theory, a branch of mathematics, the Langlands dual "L""G" of a reductive algebraic group "G" (also called the "L"-group of "G") is a group that controls the representation theory of "G".If "G" is defined over a field "k", then "L""G" is an extension of the absolute Galois group of "k" by a complex Lie group.