Multiplets of representations and Kostant's Dirac operator for equal rank loop groups

Details Multiplets of representations and Kostant's Dirac operator for equal rank loop groups Multiplets of representations and Kostant's Dirac operator for equal rank loop groups

2000-05-05

arxiv.org/abs/math/0005057v2

Mathematics

Representation Theory

30 pages. Revised to clarify use of normal ordering in Section 7 and to correct various minor errors

Scientific paper

Let g be a semi-simple Lie algebra and let h be a reductive subalgebra of maximal rank in g. Given any irreducible representation of g, consider its tensor product with the spin representation associated to the orthogonal complement of h in g. Gross, Kostant, Ramond, and Sternberg recently proved a generalization of the Weyl character formula which decomposes the signed character of this product representation in terms of the characters of a set of irreducible representations of h, called a multiplet. Kostant then constructed a formal h-equivariant Dirac operator on such product representations whose kernel is precisely the multiplet of h-representations corresponding to the given representation of g. We reproduce these results in the Kac-Moody setting for the extended loop algebras Lg and Lh. We prove a homogeneous generalization of the Weyl-Kac character formula, which now yields a multiplet of irreducible positive energy representations of Lh associated to any irreducible positive energy representation of Lg. We construct a Lh-equivariant operator, analogous to Kostant's Dirac operator, on the tensor product of a representation of Lg with the spin representation associated to the complement of Lh in Lg. We then prove that the kernel of this operator gives the Lh-multiplet corresponding to the original representation of Lg.

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