Read e-book online An Elementary Introduction to Groups and Representations PDF

By Brian Hall

This textbook treats Lie teams, Lie algebras and their representations in an hassle-free yet absolutely rigorous type requiring minimum necessities. particularly, the idea of matrix Lie teams and their Lie algebras is constructed utilizing merely linear algebra, and extra motivation and instinct for proofs is equipped than in such a lot vintage texts at the subject.

In addition to its obtainable therapy of the elemental thought of Lie teams and Lie algebras, the ebook can also be noteworthy for including:

  • a therapy of the Baker–Campbell–Hausdorff formulation and its use rather than the Frobenius theorem to set up deeper effects concerning the courting among Lie teams and Lie algebras
  • motivation for the equipment of roots, weights and the Weyl workforce through a concrete and particular exposition of the illustration thought of sl(3;C)
  • an unconventional definition of semisimplicity that permits for a speedy improvement of the constitution concept of semisimple Lie algebras
  • a self-contained development of the representations of compact teams, self sufficient of Lie-algebraic arguments

The moment variation of Lie teams, Lie Algebras, and Representations includes many immense advancements and additions, between them: a wholly new half dedicated to the constitution and illustration conception of compact Lie teams; a whole derivation of the most houses of root structures; the development of finite-dimensional representations of semisimple Lie algebras has been elaborated; a remedy of common enveloping algebras, together with an evidence of the Poincaré–Birkhoff–Witt theorem and the life of Verma modules; entire proofs of the Weyl personality formulation, the Weyl measurement formulation and the Kostant multiplicity formula.

Review of the 1st edition:

This is a wonderful ebook. It merits to, and surely will, develop into the normal textual content for early graduate classes in Lie team thought ... a big addition to the textbook literature ... it really is hugely recommended.

― The Mathematical Gazette

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Extra resources for An Elementary Introduction to Groups and Representations

Example text

It follows that for each fixed t, A t m t X m +O 1 m2 = I+ t X m +O =I+ . Then, since A is a one-parameter group A(t) = A t m m 1 m2 m . 8 from Section 3 shows that A(t) = etX . 5. The Lie Algebra of a Matrix Lie Group The Lie algebra is an indispensable tool in studying matrix Lie groups. On the one hand, Lie algebras are simpler than matrix Lie groups, because (as we will see) the Lie algebra is a linear space. Thus we can understand much about Lie algebras just by doing linear algebra. On the other hand, the Lie algebra of a matrix Lie group contains much information about that group.

Thus the Lie algebra of GL(n; C) is the space of all n × n complex matrices. This Lie algebra is denoted gl(n; C). If X is any n × n real matrix, then etX will be invertible and real. On the other d hand, if etX is real for all real t, then X = dt etX will also be real. Thus the t=0 Lie algebra of GL(n; R) is the space of all n × n real matrices, denoted gl(n; R). Note that the preceding argument shows that if G is a subgroup of GL(n; R), then the Lie algebra of G must consist entirely of real matrices.

Suppose that X is a diagonalizable matrix. Show, then, that adX is diagonalizable as an operator on gl(n; C). Hint : Consider first the case where X is actually diagonal. Note: The problem of diagonalizing adX is an important one that we will encounter again in Chapter 6, when we consider semisimple Lie algebras. CHAPTER 4 The Baker-Campbell-Hausdorff Formula 1. The Baker-Campbell-Hausdorff Formula for the Heisenberg Group A crucial result of Chapter 5 will be the following: Let G and H be matrix Lie groups, with Lie algebras g and h, and suppose that G is connected and simply connected.

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An Elementary Introduction to Groups and Representations by Brian Hall

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