Highest-Weight Theory

  • Roe Goodman
  • Nolan R. Wallach
Part of the Graduate Texts in Mathematics book series (GTM, volume 255)


In this chapter we study the regular representations of a classical group G by the same method used for the adjoint representation. When G is a connected classical group, an irreducible regular G-module decomposes into a direct sum of weight spaces relative to the action of a maximal torus of G. The theorem of the highest weight asserts that among the weights that occur in the decomposition, there is a unique maximal element, relative to a partial order coming from a choice of positive roots for G. We prove that every dominant integral weight of a semisimple Lie algebra g is the highest weight of an irreducible finite-dimensional representation of g. When g is the Lie algebra of a classical group G, the corresponding regular representations of G are constructed in Chapters 5 and 6 and studied in greater detail in Chapters 9 and 10. A crucial property of a classical group is the complete reducibility of its regular representations. We give two (independent) proofs of this: one algebraic using the Casimir operator, and one analytic using Weyl’s unitarian trick.


Irreducible Representation Classical Group Weyl Group Simple Root Maximal Torus 
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Copyright information

© Springer-Verlag New York 2009

Authors and Affiliations

  1. 1.Department of MathematicsRutgers UniversityPiscatawayUSA
  2. 2.Department of MathematicsUniversity of CaliforniaSan DiegoUSA

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